BC GTA

Here is an interesting idling problem.

If you start the car, both if it cold or warmed up, and drive off then it will idle at where the car started or at about 2000 RPM. For example when you depress the clutch pedal or travel slowly in heavy traffic the engine is stuck at 2000 RPM. However, if you come to a complete stop and let it idle down to about 700-900 RPM then it will idle at 700-900 RPM the next time you come to a stop, depress the clutch pedal or travel slowly in heavy traffic. It almost seems like you have the bring the car to a complete stop and let the engine reset the idle then it will be fine until you turn the engine off and on again.

The entire cold air induction system was recently overhauled with an AFPR, new injectors and everything cleaned very well. In fact this annoying problem occurred right after this project was done. The IAC valve and TPIS were removed from the throttle body, which was cleaned in a parts washer as was the plenum, runners, manifold and ERG valve. Everything was ported at this time. Could this be a sticking idle air control valve? Any thoughts on what could be causing this?

thunder85

iTrader: (1)

most likely its your iac like you suspect. i had that issue, mine was filthy.. just bought a new one and was good to go. could also be the tps sensor... have u tested the voltages?

bgood71

It could be the IAC, as thunder said. You sould also check to make sure that there are not any vacuum leaks being that you had the entire intake off. The most likely places would be hoses...vacuum and air intake.

pandin

BC GTA "Comp Cam Extreme Energy Cam XR258HR"

HR10 LCA 110?

What do you think of the cam?

Have you done any tuning yet?

Do you have a spare screened MAF?

This is an air flow issue with the maf system. At a certain air flow the ecm holds rpm for a few seconds then drops. With higher air flow it hangs longer.

I have a 383 and a 750 rpm auto, same cam. One Maf I have, that only flows 187 gr/sec (peak), works okay, but the ones that flow over 205 gr/sec (peak)and up, hang at 1200 rpm then drop. If I shift into neutral, it will drop, in about the time it takes the light to change,

BC GTA

Thank you for your comments. I will get a new IAC valve and try that. When the cold air induction system was overhauled I gave my licensed auto mechanic a copy of how to set the TIPS and IAC valve so I guess he set them correct. I will look for leaks in the vacuum.

I like that cam. When I changed my engine all I told my mechanic (a different one at the time) was that I wanted more power and wanted a smooth idle. I had not really discovered this website and learnt what I have learnt. My mechanic contacted Comp Cam and they recommended that cam.

It produces a lot of torque. I know there is sort of a rule around here not to go below 112 LSA; however, I do not seem to have a problem.

After participating on this website and researching TPI engines I have educated my self and I may have done things slightly different when the engine was done. However, all in all this combination has given me what I wanted i.e. more power and a smooth idle.

Sorry I do not have a spare MAF sensor. The car has been tuned several times since the engine/cam/headers were installed a few years ago and after the cold air induction system was rebuilted last summer. The mechanic who did the engine a few years ago was setting the timing at 0 degrees before TDC. The new mechanic has backed it off to like 6 or 8 degrees before TDC when the induction system was done.

pandin

With my heads, motor, stock chip, and cam, comp's cam quest put out 382 hp @ 4500 and 538 tq @ 2000. Datamaster's dyno (from a 1/4 mile test run)came up with 300 hp and 420 tq. This is - 20% of the comp numbers.

I thought about a higher rpm cam, but 55 mph = 1550 rpm @ 12 hp load. This combo gets 15 mpg to work and 20 mpg trip. Also it needs tuned (programing parts ordered).

BC GTA

Here is an update to this post. Two more problems recently developed. First, you have to crank and crank to start the engine in the morning. Second, when driving along the engine seems to stutter or miss fire. The previous idling problem persists.

So I took the car to my mechanic who first suggested turning the ignition, but not the engine, on three times in the morning to pressurize the fuel system. That did little with the hard cold starts. Then I changed the distributor cap and rotor. That did little to address the problems.

Then we had a mechanic experienced with Chevy engines look at it. We swapped in a new Bosch mass air flow sensor (see new post on upgrades Bosch has made) and engine began to run and idle much better; however, the original idle problem continued. The hard cold starts got a little better and the miss firing went away. We checked the TPS and IAC valve, which did nothing to solve the remaining problems.

Then we decided to check for vacuum leaks. My mechanic recently bought a vacuum checking machining which pumped a gas or smoke through the induction system. We found a small leak at a “T” plastic part back by the distributor and replaced it and small leaks around the valve cover gaskets. However, smoke just gushed out of both sides of the throttle body butterfly valve shaft bushings. My mechanic suggested the bushings must be gone. This throttle body is the original one with about 229,000 km on it. When we rebuilt the induction system we removed the TPS and IAC valve and washed the throttle body in a parts cleaner. I doubt cleaning the throttle body would have done this

Anyhow it looks like I need to replace the throttle body. So I have a few questions.

1. Has anyone rebuilt the original GM throttle body to put new bushings in? If so please provide information. I once read somewhere that someone bored out a throttle body from twin 48 mm to twin 52 mm or 58 mm and rebuilt the shaft. However, by the time I pay a machinist to do this I could buy a new aftermarket throttle body.
2. If I get a new aftermarket throttle body I am thinking of the twin 58 mm by Holley or BBK. I see Summit Racing has some cheaper ones. I know it has been discussed many times that out cars do not need the bigger throttle bodies but if you are replacing it you might as well get a big one.

I know this has been long and detailed posted but hopefully it should provide good diagnostic information for others in the future.

bgood71

If you replaced the MASS and it helped, try unhooking the battery -. That'll clear the comp memory and may help with the idle. When i replaced my MASS, the car actually ran worse until I cleared the memory. It now runs better that it has since I.ve owned the car. Hope this helps, gl.

BC GTA

I will try resetting the ECM by disconnecting the battery and give that a try. However, I suspect so much air is leaking in by the throttle body shaft, especially when the engine is cold and the metal parts have not expanded, that the MASS is reading a low airflow. Consequently, the ECM is told of this low airflow and trims the amount of fuel to the injectors and you have to crank and crank to get the car started. Does that seem reasonable?

So I went to a respectable automotive machine shop and had a machinist look at it. He recognized the problem with leaks downstream of the MASS right away. He estimated to put in new bushings where the butterfly valve shaft goes into the throttle body would be approximately $75 to $150. I will decide between a new bigger throttle body or rebuilding the original one in a few days.

pandin

Re: Looking for advice
The reason for the vacuum test is this, if there is no vacuum drawn, then the bigger holes will not likely make a big difference.

Carbs are cfm rated at 1.5" for 4B and 3" for 2B.

Stock 85-87 Firebird TPI airbox mid piece -- 499.3 cfm
Stock 88-92 Firebird TPI intake bellows w/ integral 90 degree bend -- 693.0 cfm

Stock MAF .................................529 CFM
Screens out................................711 CFM

Stock throttle body......................668 CFM

Stock throttle body w/TPIS airfoil...709 CFM
equivalent to a carb rated at.........787cfm

305 @ 80% VE 6000 rpm...............450 cfm
305 @ 100% VE 6000 rpm.............530 cfm
305 @ 100% VE 7000 rpm.............618 cfm

If you have a stock TC and 2.73 gears a 58 MM could be grabby. 3.73 and a 3000 stall would be less of a problem.

Do a search on 58MM and 305.

BC GTA

So I have probably decided to have the stock throttle body rebuilt with new bushings for three reasons. First, as has been discussed many times the bigger bore throttle bodies will not permit any additional air flow to be drawn into a 5.0 liter. Second, I inserted my finger into the stock throttle body and could feel the 48 mm bore was flush with the bores on the plenum. A larger throttle body would require additional porting of the plenum, which would again not produce any more airflow and would only add to the cost. Furthermore if the plenum was not ported with a 52 or 58 mm throttle body the obstruction could actually impede airflow. Third, why spend more money for no additional gains.

If I come across any interesting issues having new bushings installed on the stock throttle body I will post them.

BC GTA

I thought I would update this post. So I had the throttle body rebuilt by having new bushings installed. The machine shop had a difficult time; however, they finally got it done. A few days later we did the smoke/vacuum test and nothing came out of the throttle body blades shaft so they were able to fix it. There are no other vacuum leaks. I could provide any one with the name and phone number of the machine shop that did this for the procedure; although, I suspect any good machine shop could do this.

So I still have the annoying problem of what my mechanic calls idling up. When the car is hot or cold and you start the car up and drive off it will idle at about 2000 rpm. If you come to a full stop and let the car idle down to where it should be at about 800 RPM it will then idle properly. The car also has to crank a bit in the mornings when it is cold. When it is hot it start up right away.

We are going to plug in a scanner this afternoon and go for a drive and analyse the situation. Does this sound like an idle air control motor problem? We boosted the fuel pressure to 49 psi a few months ago when the AFPR was installed, could that have any thing to do with this and the hard cold starts? Thanks for your thoughts on this. I will up date this as new information becomes available.

upandcoming

iTrader: (20)

sounds like the Iac valve needs adjusted..Have you changed chips???or have you changed out your fuel pump lately??

pandin

If you are running a stock chip the only thing more fuel pressure will do is lower the blm's (rich) until you hit the blm limit then the motor will go rich (108 blm).

When you installed the new maf it will raise (richen, more air more fuel) your grams/sec (lower blm's).

Old Maf's get smaller (leaner, less air read, higher blm's) as they age (I have seen many that peak at 190 to 200 not 255). This is on the same 383 motor/car (just changing the Maf). On a stock 350, you would never know without scanning (they don't pull enough air).

By increasing the fuel pressure you compensated for this lower grs/sec output from the old Maf. With the new Maf the blm's are now likely lower (more air, richer) so the added fuel pressure might be overkill (lower blm's richer) after a 108 blm is reached (way rich).

While I was waiting for money for tuning equipment, I used this technique to adjust the fuel on my car, 50# fuel pressure 24# injectors and a 187 peak Maf ran the best with a stock chip. Idle was 160 blm but all the rest were 128 or so. Car got 15 town and 20 trip.

Any change inside the ECM's area of compensation will only affect the numbers and any change outside this area will also affect the tune.

BLM's can go from 108 to 160 and there will be little change in the running of the car in closed loop conditions.

It acts like slop in an old manual box steering. You turn the wheel, nothing happens, so you turn it some more, nothing happens, so you turn it some more and all of a sudden the car turns, but too much so you turn it back, nothing happens, and so you go zig zagging down the road chasing the slop.

BC GTA

Thanks for your comments. I have a relatively new high volume fuel pump. We also tried turning the ignition on a few times without turning the engine on to pressurize the fuel system. This did not address the cold start problem. I also have the original PROM chip as I am the original owner of the car. As I have now done all I want to do to this engine once these idle and cold start problems are fixed I plan on getting a custom chip burnt for it. I have found a mechanic in a city close to mine who also burns chips and can do it while test driving the car.

After driving the car hooked up to a scanner we determined the idling up problem is caused by the IAC motor. I have ordered a new one. When it gets here and is installed I will post the results. The hard cold starts in the morning improved somewhat by sealing up all the vacuum leaks; however, it is not completely solved. Possibly the IAC is leaking air in the mornings or a mechanic suggested this is usually attributed to the timing being off. When we install and set the IAC I will have them look at the timing. I think the timing for these cars is 10 degrees BTDC and I as I mentioned earlier it is set at 6 or 8 degrees BTDC. May be I will get them to set it at the factory setting which I think is 10 degrees BTDC.

pandin

Factory is 6 and it has to match the Prom. Too much initial timing will make the engine hard to turn over (low or slow cranking speed) and hard to start.

BC GTA

Yep I looked it up in a Chilton's this morning stock timing is 6 degrees. Will have them check this when the new IAC valve is installed.

BC GTA

Here is an update to this thread. We installed the new idle air control valve yesterday; however, the same three problems persist. We also checked the timing. They found it bounces around a bit, which may be due to the cam. To recap these three problems are the idling up, hard cold start and rough running or apparently misfiring when just cruising along in town. It seems to accelerate nicely. These problems occurred just after I installed the new FMR fuel injectors, the Holly AFPR and ported the plenum. We have installed a new Mass Air Flow sensor, recently a heated three wire O2 sensor and an IAC valve. So tomorrow we try swapping in a new computer. Stay tuned as we explore this option.

Shadygrady

iTrader: (3)

Subscribed.having similar problems.

navyCM

iTrader: (3)

why do people just jump to changing out ECMs. they just dont go bad. its usually something under the hood causing the problem.

bgood71

If the timing is jumping around you may want to suspect the distributor.I had the same problem with my 87 T/A...a reman dist fixed it .

BC GTA

We are only considering the computer after changing several sensors and the distributor cap and rotor. The distributor is only a few years old and is a MSD Pro Billet distributor. I will mention the distributor to my mechanic when I see him in a couple of hours. Is there something to look for with the distributor?

bgood71

You'll want to remove the cap and rotor and inspect it for a white powder and/or corrosion around the shaft. If there is the powder ,its an indication of the dist...it was explained to me as oil seeping up the shaft and becoming a powder when being inside the cap with the spark. If there is rust you are getting moisture in the dist. , I would suspect the hood seal leaking at the back of the hood....it'll drip water right on the plenum extension, or dist if the extension is missing. GL, hope you get it worked out soon.

BC GTA

Ok I am back at my mechanic's shop now. Yestarday we found that someone had screwed in the idle screw several turns too much, such that it was holding open the butterfly valves. We backed the screw off to the point where it did not move the butterfly valves and reset the TPS, which was at .40 and reset it to .54. That may have helped somewhat. This morning we will reset the new IAC valve. I will have them inspect the distributor. We are trying one thing at a time. My mechanic says he does about 15 computor swaps a year. We have not gone there yet. Hopefully, we can track down this problem without swaping in a new computor.

BC GTA

So we diagnosed the idle problem. When the throttle body was rebuilt with new bushings the butterfly valves were slightly out. This caused the valves to rub on the bores of the throttle body. The spring wrapped around the butterfly valve shaft was not strong enough to pull the valves shut and the TPS was held open a bit which caused the engine to rev and idle high. Then when the car came to a complete stop the vacuum from the engine was enough to pull the valves shut. So we tested this theory out by attaching some rubber bands (yea, yea, I know mickey mouse) to pull the butterfly valves shut. That worked to correct the idling up problem. Then on the weekend I was able to work the coiled spring around the butterfly valve shaft one more revolution to increase the tension. It is a bit of a trick to do this, you poke the bent end out of its retaining slot and pull it around with a piece of string. Anyhow this did not provide enough tension and I when to my local auto parts store and bought a throttle return spring which did produce enough tension. It looked OK but I like to keep things looking original as possible so I went to the machine shop that rebuilt the throttle body and the machinist took some emery cloth and inserted it between the bores and the butterfly valves when they were almost closed and pulled it through to work down the valves where they were rubbing. We got most of it done and on the advice of the machinist I have been using some 320 wet and dry sand paper to do the rest. This is working and I will either get the rest sanded down or let the valves seat in such that I can remove the throttle return spring and just let the coiled spring close the valves.

We inspected the distributor and found it was OK, but it was a good idea to track down one more thing.

We did swap in a new computer and this has helped with the other problems. I have been test driving it over the weekend and tomorrow will go to my mechanic and have everything put back together – the computer is exposed while I test everything out.

Hopefully this thread has provided some diagnostic information for people with similar problems. If I come across anything else I will update this thread.

BC GTA

I came up with a good trick to help determine where the butterfly valves were rubbing. Take a felt pen and colour in the bottom of the throttle body bore just where the butterfly valves close and the top edge of the butterfly valve. Then close the valves and observe where the felt pen colour has been worn away. You may have to colour the parts a couple of times to confirm that is indeed the area that is rubbing. Better to measure twice and cut once rather than sand down the wrong area.

BC GTA

Ok we found another problem causing rough idling and also the miss firing yesterday. We took out all the spark plugs and did a compression test. The compression was fine with only 44,000 km on this engine. What we found was one of the spark plug was completely fouled such that there was practically no gap left. We did a resistance test on the MSD 8.5 Super Conductor wire and found it was good; however, the boot up by the distributor cap was cracked as were a couple other wire boots. The boots down by the spark plugs were all good. So I went and got a set of 9 MSD boots part # 8851 and we will install them tomorrow. To update we did end up putting in a new ECM, which helped. So if your idle is rough you may want to pull your spark plugs and test your wires and inspect the boots on either end of the spark plug wire.

BC GTA

So we installed new boots which definitely helped. My mechanic use to get shocked when working near the distributor, now you can place you hand on top of the wires with no problems.

I just finished calculated my new gas milage after all this work. Before in the city I was getting 16 mpg to 16.5 mpg. Now I am getting in the city almost 18 mpg.

The idling up problem is solved. The hard cold start problem is solved. Most of the misfiring or jerkyness while the car is just crusing along is gone. I do notice sometimes when the car is ilding I can hear a god allfull rattle. I removed the TPI distributor cover (not the cap) and placed my ear down by the distributor and the rattle seems to be coming from the transmission. Therefore, I think the misfiring or jerky feeling is actually something slipping in the transmission. Soon I will get a transmission shop to look at this.

freestylzz

I used to have a hard cold start, rough idle, misfire in cruise, and backfire at wot.

After testing I found half the injectors were faulty.

If anything, have you at least inspected the OHMs on your injectors?

BC GTA

Last November we replaced all the fuel injectors with FMR injectors, installed a Holley AFPR and ported the plenum. So all the fuel stuff is new.

Theking

iTrader: (1)

I also have some problems, it starts to wanderar like 50 to 75rpm on idle with gear in, and its a pain in the *** to start when its hot, getting strange/bad rpm signal needle jumps from 0 to 7000rpm and sometimes get stuck at 7000rpm need to rew it up to get the rpm gauge to work again..

Changed the ignition module and pickup on my brand new MSD 8366 distributor, problem was gone some days, then now its back agian...
Could it be the distributor again... Got a thread on this in TPI part, "changed injectors and..." Seems like my distributor cuts out when its getting hot..

bgood71

Sounds like you have gotten the car in good running order BC. If you still have a little buckin/surge while cruising and think it may be the trans, try unplugging the lock up switch on the trans. Its a 4 wire switch near the the driver front part of the trans, close to the shift linkage. The switch controls the torque converter lock up...so you may have a failing torque converter.

BC GTA

Yes, we are definitely getting there.

This problem showed up really bad in November 2007 and water was leaking on to the intake manifold so I decided to fix that and undertake the fuel injector project at that time. So to date we have installed new fuel injectors, installed an AFPR, ported the plenum, installed new intake manifold/runner/plenum/throttle body gaskets, fixed several vacuum leaks including a bad one with the throttle body, adjusted the sticking butterfly valves, installed a stronger throttle return spring, replaced the mass air flow sensor, replaced the idle air control valve, checked and set the TPS, reset the timing, installed a heated O2 sensor (that was a separate project), installed a new computer, checked the compression of all the cylinders, installed new two pronged platinum spark plugs, checked the MSD spark plug wires and installed new top end spark plug wire boots and checked the distributor. That is all on top of a new 5.0 liter engine from GM that was installed a few years ago, which now has about 44,000km on it.

The MSD distributor is a couple of years old. When an ignition module starts to go what would you start to notice. What are the symptoms of a failing ignition module? Can you just plug a new one in without timing the engine? I know they give you some oil to place under the ignition module for cooling. Does anyone remove the module and renew this cooling oil?

I have a manual transmission, which has 240,000km on it. When the engine was installed we did the cam and headers which probably increased the torque. So the engine has been pumping out a lot more torque on an old T-5WC transmission, which was not designed to take much more that a stock 5.0 liter TPI engine.

BC GTA

Here is an update to this post. So I went to a highly regarded transmission shop who are also getting into general auto repair.

They noticed my idle was sticking or coming down very slowly and found a vacuum problem with the EGR valve which is now getting replaced.

In addition to the work I mentioned above I also replaced the distributor cap and rotor.

So the following should probably be on the transmission board but I will mention it here. The jerkiness was due to a shot clutch. The transmission was removed and disassembled. There was a little scoring on the main shaft, the syncros were showing a little bit of wear, the plastic things on the aluminum shifting fork were worn and the gear that comes with the main shaft that engages the reverse gear was a little worn; however, they were amazed at how good the gears were in after 231,000km. I saw the gears and literally there was no scratches on the gears.

We discussed G-Force gears, Cobra upgrade and a couple of other options; however, for how I drive the car we are just going to rebuild this one with a new main shaft and the gear that comes with it. The first to fifth gears were in amazing condition. A new clutch will be installed. This should cure the jerkiness.

We also looked at the differential and a pinion bearing is just starting to go, the posi thing is just about shot and a wheel bearing is going. The ring gear does not walk from side to side at all. They did a wear pattern test on the ring and pinion gear and it was good. The ring and pinion gears were in very good shape also. So the differential will need some work soon. Apparently, I have a 9 bolt Australian differential 3.45:1 ratio. I will do some searching and questioning on my options over on the transmission board. But I just thought I would post my experiences here.

jays1234

my car 91 rs l98 350 had rough idle no idle and misfiring hard start till i replaced pickcup coil ran soo much better i allso replaced icm after pickup coil runs awesome now

BC GTA

So they removed the EGR valve and found it was stuck open. They also previously noted the EGR valve was sending incorrect signals to the ECM such that the IAC valve was not functioning properly. I will let you know how this turns out.

pandin

Please note there are two ways to get "EGR valve was sending incorrect signals to the ECM".

The feedback is a temp sensor (seperate from the EGR, $15.00), low temp EGR is closed, high temp EGR open.

1 Defective EGR, good senor circuit.

2 A bad sensor or loose/corroded wire/connection will also give "incorrect signals", idle would not be affected.

Any time the engine runs way rich for a long time, issues with the EGR, Cat, IAC, can also remain after the rich condition is fixed (injectors, ignition parts, O2, air cleaner, Tune).

BC GTA

Upon inspection they found, which was shown to me, the EGR valve was sticking open resulting in a big vacuum leak. The EGR sensor had about 100,000 km on it so it was getting old. Interesting you should mention the temperature sensor thing, the mechanic touched the wire going to it and it crumbled so it had to be replaced as well.

I got the car back yesterday and it appears to run much better. It better considering all that has been done to it in the last eight months. I will really take it for a test drive today and then I have to take it back to the shop in two weeks for an inspection.

So the transmission was completely overhauled. The syncros were completely worn and some of the bearing were worn. A new clutch was installed so the god all full rattle is gone as is the jerkiness.