Ok, I've read around 300 different posts on TPI problems and ajustments and have tried most everything the different posts suggested.

The car is a 87 305 TPI 5spd. The car sit for 4 years, and we got it out and put a new clutch in it, then lost the T5 500 miles later. I just got the T5 rebuilt and put back in yesterday. I also did the valve stem seals while I was waiting for a new cluster gear to come in. Problem is a major stumble just off idle. The 02 sensor has been replaced 50 miles ago (with OEM Bosch), just put a new TPS on and adjusted the voltage correctly (today). Got the closed throttle voltage at exactly .54, and WOT voltage and 4.37. The new TPS voltage increases steadily when you open the throttle. I cleaned the IAC and that helped the idle quite a bit. It has new cap, rotor, new plugs. Good jacobs plug wires on the engine, and new fuel filter. (yesterday also) It did the same thing before changing the valve stem seals, so nothing I messed up there. (it's sure nice to start the car now and not have a smoke screen!!) The car will accellerate good when cold, but after about 5-7 miles (in 75 degree weather) it stumbles badly just off idle, and continues to do so until you let off the throttle. No mater how far you push the throttle down, it stumbles until you let off it. It will cruise ok, you just can't give it any throttle. If you stop the car and hit the throttle, it wil leasily hit 5000 rpm. Just can't give it any throttle while driving. There are no error codes in the computer. The in tank fuel pump was replaced just before the car was put in storage. From reading posts, the problem seems to be when the system goes into closed loop mode. I havn't checked fuel pressure, but since the car runs good when cold, not sure if this is worth checking.

This thing is driving me nuts. I've got this great car and now a really sweet shifting T5 and I can't give it any throttle. Anyone have any ideas? I certainly would appreciate your input.

Thanks-Dan

 

Mines doing the same thing! Look at "off-idle stumble" by 90Iroc.

 

I saw your post and we seem to have the same problem, but have done different things to try and cure it. I've relaced the TPS, and 02 sensor. My car was also sitting for 4 years. Considering how "touchy" the TPI system is, I decided to post seperately with all the things I've tried to do to fix my problem. Maybe someone will have the answer for both of us.-Dan

 

It may sound stupid, but check your Coolant temperature sensor that goes to the ECM. If that thing is broken the computer thinks the engine temp is at -2 degrees and adds a whole mess of fuel after it goes into closed loop. Check with a scanner, it's the easiest way then replacing the whole sensor.

 

I don't have access to a scanner. If it comes down to that, I'll have to take it somewhere to have a scan done.

 

Do it the easy way, get your car warmed up and drive to the auto store. Buy the CTS sensor and plug it into your harness, and just drive around with the new one plugged in but not installed into the proper location. It'll read whatever the air temperature is outside, but the car should run better than thinking it's -2 degrees.

 

Markoloc,

You really think it's the coolant temp sensor? Would a faulty sensor shut the car down like this when I give it some throttle? Never thought of that. So installing the sensor when the engine is warm gives the computer a false temp baseline and makes it thinks it's colder outside?

 

A car sitting for 4 years? I'd replace the injectors or at least have them cleaned and flow checked, they are nothing more than an electric solinoid that opens and closes to let fuel past. They are a pretty close tolerance device and will not tolerate deterioration of the winding insulation or corrosion build up inside them.
Also check the MAF, there is 4 years of crud built up on it from sitting around not running. Check ALL electrical connections for corrosion in them and at all ground points. Letting an electronic car like that just sit for that long is one of the worst things you can do to it.

 

I've already checked and cleaned all ground cables. The only corrision problem I've seen with the car since we put it back on the road was the dome light socket needed to be cleaned. Other than that everything seems fine. The MAF looks like it's new. I also replaced the CTS today. It was only $8 from the "Zone". This problem definately seems to be temperature related. The CTS seemd to have helped, but I took my "test" drive tonight when it was 20 deg. cooler and it seemd to take forever to act up. And when it did act up, it wasn't as bad with the new CTS. Seemed to take about 1/2 hours to start acting up. Before that it was running strong. Easy to break the tires loose in 1st. and pulled hard up to 5000rpm. It's got 144 k on it, so 5000 is enough in my opinion. I'm thinking seriously about an auto xray unit. I can get one for $150, and then sell it on Ebay for about the same as I paid for it. Other alternative is to take it to a shop and have it scanned. I still have no codes in the computer to read. Just flashes #12.

Thanks-Dan

 

Don't shell out the $$ for a scanner, get a cheap used laptop from somewhere like E bay (can get a good one for $50-$75), spend another $4 for supplies to make a cable and down load either Craig Moates' scanning software or Winaldl (also free).
Viola! Good cheap scanner that can do MUCH more than a handheld could ever think about.

Note: The laptop doesn't have to be a big powerful machine, some people run the scanner on 486's and I'm running it on a lil ole P120.

 

Morley, I've got a laptop I forgot I had. It's a 200mhz pentium with win95, but the battery is completely dead. New battery is $100 with shipping. Haven't found a used battery for it yet.

I looked at Craig Moates site, but wasn't sure which software it was I needed to download, and didn't find the link to making the cable. Can you clarify this for me? I would certainly appreciate it.

Aftert this problem is fixed, I want to try and burn a new chip for it. We had turbo city do this chip and it works well. The first one he did didn't even get me out of the driveway. The second one went in around 50k ago, and on a trip to LA we got 30.08 mpg with the AC on 100% of the time. Even running crappy like it is now, it gets 22 or better in town.

 

Here is the link to the page with everything you need. http://moates.net/gmecm/software.html
I am using the 2 transistor cable and the ECM851 software, I can't get the cable to work with the 852 software.

As far as the laptop battery goes, just get a cheapie power inverter that plugs into the cig lighter and run it off 110 power.

 

Have you checked your EGR?

 

We haven't checked the EGR. I assume you pull it off and see if it's carboned up. Am I correct on this? I did get a code 32 once about 4 1/2 years ago, about 6 months before it was put into storage. (I keep a log of problems with every car I own-especially the computer controlled ones and this is the only trouble code this car has ever had since buying it new)

If I do have to pull the plenum to replace the EGR valve, what do you guys think of putting an adjustable fuel regulator on at the same time? You have to pull the plenum for both, so why not put an adjustable fuel regulator on at the same time? Any thoughts on this?

As for a power inverter, I have a huge one on my pickup I use for my cargo trailer for running drills and stuff when we are out riding our ATV's. I had considered using this, but it's a major deal to install it correctly, and I didn't want to butcher up a temporary install on the camaro. I didn't know there were smaller ones available that just plug in. Doesn't take much to run a laptop, so I will look for one of these. Thanks for the idea.

I'm leaving on vacation on Thursday, so probably won't be able to do much before then. It's probably good that the car isn't running correctly. My kid will have access to it, and that's all I need is to have him wrap it around a tree. Maybe this is meant to happen!! It's bad enough he has access to my pickup with a 468 in it. But it's so low geared you can't do much with it, and besides it's not as "cool" as the camaro is.

Thanks-Dan

P.S. Forgot to mention, car has K&N filters on it, so no air flow restriction there to worry about.

 

Try changing your mass air flow sencer because mine was doing the same thing the other day and i went out and got one and it fixed the problem. The burn off relay might be bad

 

I just found out that the fuel pressure is not holding. I have 46 at idle with the vac, disconnected, and 36 with it connected. I have 46 with ignition on, but engine not running, but the pressure drops like to zero in 10-15 seconds. I pinched the pressure hose from the fuel pump off and it maintains pressure after I turn the ignition off. My TPI book tells me that my pump is bad if it holds pressure with the line pinched off. With the pump not holding pressure, can this be the cause of the stumbling?

 

Well for everyone that posted suggestions to try and help me fix my stumbling problem I say thank you. I finally got time to work on the car again and found the problem to be the EGR valve. I replaced the EGR valve and EGR temp sensor with GM parts and it runs great now. The engine will effortlessly wind up to 6000 rpm now without any miss or hesitation. There were never any codes that showed. The only code I got was 2 days after I had the car running. Got a code #15. I replaced the "new" cts with another "new" CTS and it took care of that problem. The CTS that failed only had about 1 hour of run time on it.

To me it seems strange that the tach needle would drop when the car stumbled, then you let off the throttle the needle went back up. In discovering this I was sure it would be distributor related and took a distributor out of another engine and rebuilt it, but wanted to get the intake back together and get the engine running again before changing the distributor. One thing at a time so to speak. But putting in the new distributor wasn't necessary.

I'm posting this in a effort to help others with a stumbling problem. Hopefully my experience will save time and trouble for others.

 

Throttle Position Sensor: Probably
CTS (Coolant Temp Sensor) : Maybe
EGR Valve: I'll bet it's this

 

no 1 cause of stumble off idle with an engine with more than 60 thous miles on it is CABON build up on the intake valves..........use a good cleaner and afterwards change the engine oil

 

Thanks for your ideas guys, but the problem is solved. I know my last post was long, but if read completely you would see I've found and taken care of the problem. I just wanted to let people know what I went through and the final solution was the EGR valve.

Thanks
Dan

 

I knew it! lol That damn EGR did the same thing to me. I never fixed it..just unhooked the egr to solenoid vac line. been great for years now. Oh, I do plug the sucka back in for emission testing and it still does enough for me to pass.