CreativeIndy

iTrader: (1)

I have an 87 Iroc 5.7 that currently has a 5.7 out of a 90 GTA in it. I bought the car not long ago and the PO told me the car has a rough idle that's hes been chasing but never has found it. He told me he checked everything, replaced the ECU, MAF, fuel pump, almost all the sensors, had the injectors tested, cleaned the IAC, checked every inch of the top end etc and still never got rid of the stumble idle.

I get the car home and take it out for a spin and sure enough it putts and vibrates at idle, it runs decent under load it has decent power. but I can still tell it has even a stumble at speed. I spend the following 3 days looking over everything trying to see if he missed anything. Everything seems normal as far as I can tell.

So my first thought after a few days of chasing and searching I decide to toss the TPI in way of a carb setup. Cheap, and quick fix of the issue without throwing a ton of cash at the car replacing the TPI system. However, upon taking off the throttle body I notice some bad stuff. This is where I need the advice. I was told he cleaned the TB but if you look at the images below he did not clean it. The gasket was brittle, the TB came off super easy so the gasket wasn't stuck, however part of it seemed broken. This could have been from me separating the 2 parts.

What I need to know is could this cause the issues this motor is having? I don't mind replacing the gasket real quick and throwing the TB, MAF and wires back on to fire it up. I just don't want to go through all that mess if it's not capable of causing the issues this car has. Right now I am stopping removal of TPI to carb swap until I get some feedback. Sorry for the long post, just wanted to make sure I got the details in here.

skirkland1980

iTrader: (2)

That depends id the idle speed is too low to keep the engine running. If so then cleaning the tb should help. Also a malfunctioning egr valve can cause a poor idle since inert gas doesn't burn.

GOATS2QUICK

iTrader: (5)

looking at the pics, it seems the gaskit may have been leaking , causing the stumble.

Tuned Performance

iTrader: (92)

im not sure if that is residue from cleaning or the tb mounting gasket was blown out causing a vacuum leak. This is a 85-88 plenum and throttle body not a 90. You should clean up the tb real well and clean the gasket surfaces and reset the min idle speed. Too many people chucking tpi for carbs because they don't understand them or want to work on them. The rough idle can be caused by bad injectors as well.

CreativeIndy

iTrader: (1)

Idle speed isn't low at all. It's actually quite high. It idles around 1000 to 1100 and sometimes around 1200 RPM. The idle screw is all the way out, so the linkage doesn't even hit and it still idles high. I image the reason the linkage doesn't hit the screw is because of the gunk stopping the butterflies from closing all the way? Not sure but could be one possibility. The EGR is also not bad, it appears to be brand new and I did check it as people suggested on here. However nothing is definite and it could very well be bad. However my main issue was the TB and the gunk on it. If this isn't or can't be the issue I am going to continue with my carb swap.

CreativeIndy

iTrader: (1)

You are correct on the year of the plenum. The motor however is out of a 1990 with parts from the 87 transferred to it. It's not that I don't understand the TPI, I just don't want to deal with it. Not my cup of tea and financially it was easier for me. The PO also spliced together a wiring harness due to an engine fire, so between that, and the motor running bad, and the fact I had an intake, carb, dizzy and AFPR already in the garage, the decision was easy for me.

I guess everyone has there opinions on the swap, and I can respect that. if the motor and electronics were in better shape, or if I was in the loop on every part of the swap from the PO I would try to keep the FI. I just prefer at this time to continue the swap to carb if the TB isn't the issue. Just have no desire to throw money or time at a problem that could lay in more than 20 places.

I guess for now I am going to clean it and throw it back on, fire it up and see what it does. If it runs better or fixes the stumble and idle issues it did have I will leave the TPI intact.

Tuned Performance

iTrader: (92)

I can't tell bye just a picture if the blades are getting bound bye carbon, over time the throttle shaft will wear into th tb housing and cause a vacuum leak and binding but you will need to check the play in the shaft.

CreativeIndy

iTrader: (1)

It all seems tight and in working order. It doesn't appear to be loose or sloppy. I do have a second TB that was also included with the car. The PO said he got it from a junk yard. It's actually alot cleaner than the one on it, however it has corrosion from being open to the elements.

I am going to clean this dude up, get a gasket kit, slap it back together and see what she does. I would be ecstatic if it fixed the rough idle. if it does I am going to text the PO and call him a retard for not cleaning this like he said he did. Supposedly he just cleaned this a couple weeks back.. sure doesn't seem that way.

Tuned Performance

iTrader: (92)

CreativeIndy

iTrader: (1)

^^ roger that! In that area is where I was saying above that upon unbolting the TB literally slipped right off and that part stayed on the plenum and the TB kept the rest. Almost like it had been separated recently. Wondering if someone pulled it off and bolted it back on without replacing the gasket. I know that sounds odd but I have seen people do that before on a carb motor, I could see someone doing it on a TB as these gaskets are hard to find locally.

I am going to clean the plenum, check for flat and go from there. I have a spare TB and plenum that came with the car. The spare plenum and TB are in great shape, they both have a light coating of filth and some aluminum corrosion from being subjected to the elements but that should clean up easy.

Thanks for the help. I am crossing my fingers this fixes the issue. It would save me a considerable amount of time not having to perform the carb swap.

Tuned Performance

iTrader: (92)

http://www.autozone.com/autozone/par...ier=59535_0_0_

CreativeIndy

iTrader: (1)

So I cleaned the spare TB I had, cleaned the plenum as much as I could, re-installed everything and fired the car up. It ran noticeably better I guess but there is still issues. It's a little smoother when giving gas such as the rev is cleaner and smooth. It does however still have a miss or constant stumble. It causes a pretty bad vibration in the car. It's not as bad as it was but it;s still present. The seats shake pretty bad with it running.

Last night and this morning I reset the TPS, IAC, replaced the pickup coil, reset the timing, rechecked injectors for OHM, volts and pulse, went over all the vacuum, checked the EGR it is new, checked the MAF it is new as well.

So at this point I am 50/50 on if I am going to do the carb swap. Just can't seem to nail down the rough issues and it could still be a number of things. It does have a noticeable tap from the valve covers so I am curious if the valve train needs adjusted. No telling how many miles are on the motor as I didn't install it. I've heard worse tapping before on cars so not sure if this is the cause of the continued vibration. Just seems like I have went through everything that could cause this issue. I even checked motor mounts. I'm kinda at a loss right now on where to go next. Hate to give up on the TPI I just don't want to keep wasting time or money on it.

Tuned Performance

iTrader: (92)

you might want to start pulling spark plug wires sounds like a ignition or cylinder miss, It probably would have been a better choice to get bosch 3's instead of having the old injectors cleaned
.

CreativeIndy

iTrader: (1)

Yea I am mulling over buying more parts(Bosch 3's) or doing the swap. I honestly do not want to loose the TPI. However I also don't want to throw money at an issue that could be several things.

The vibration moves with the engine RPM. If I rev and hold at say 2100 car is smooth as can be, below that or higher it gets worse etc. I have pulled the injector wires one at a time and I notice very little change. I mean, there is an initial idle change when you pull one off but after that it seems normal without it on. I thought this would be strange considering pulling an Injector should be the same effect as pulling a plug wire no?

I have a second stock distributor as well as a brand new Accel large cap dizzy. I am thinking about putting the original spare dizzy that came extra with the car on it to see if it helps. It might be a pickup coil issue or external coil as well. I could also put on the brand new Accel dizzy as a further test. I have went over every inch of vacuum lines to check for leaks. I've re-tightened every last nut and bolt.

The car runs considerably better, It really does. yet still not where I would call correct or even reliable. It is a ton smoother than with the old TB on it. Amazing what a clean TB does to a car. If I could get rid of the last bit of stumble and vibration I would be set.

Thanks for all your help man and that modified plenum with the 4 barrel on top is atrocious.

86irocdee

I'm having a very similar problem with my 86 iroc. My car idles like crap in drive at a light. It's surging and dumping a lot of fuel. I'm a diagnostic tech and at the shop I work at we have a obd 1 scanner and it says it has a bad MAF sensor. But I'm not sure if its my only problem. I looked in all data and there is a bulletin on a MAF sensor relay and burn off relay. There's new part numbers for the replacement. I just bought this car 4 days ago and I have no idea what's wrong with it. It mainly does it when it warms up. I think I'm going to check for a stuck open injector and check compression. It's really doesn't have much power at speed either. Not sure what it could be. Any suggestions?

CreativeIndy

iTrader: (1)

^^ Ours are similar. After many things new tonight including swapping the distributor to a clean and almost new one it runs better but it surges still and vibrates bad. You can unplug the MAF and see if the car still runs bad. As far as I know a car can be driven without the MAF you just won't get the best fuel economy, it will hesitate and other small things but it will allow you to see if the MAF is your issue if it solves the other issues. At least this is what I have read on multiple threads on this site in regards to running issues with the MAF as the possible culprit.

My car runs pretty damn good now when it's cold. It gets worse as it warms up, but it's still a ton better than it was when I bought the car. I think my next big issue is valve adjustment and I also heard a low thud type knock down low. It doesn't sound like metal to metal it sounds more like a deep solid thud that does move with engine RPM. I also have noise up top I can hear in the plenum. This may be injector knock sounds I am hearing.

Your problem sounds like a MAF> I would unplug it and see if it corrects some of the issues.

tpi84stepside

It's weird that unplugging injectors didnt make a noticable difference..I did that to find that I had one injector that was only working intermittantly. At idle it didn't work very well. New bosch 3's solved the problem for me.

86irocdee

hey creativeindy. i was reading a thread last night and another member was having a problem like our cars are having. he fixed it by replacing the ignition control module. it may be worth a try.

CreativeIndy

iTrader: (1)

I've already replaced my entire ignition system. The ECM, Distributor, pickup coil, ext coil, plugs, wires, cap and rotor.

When cold, the car fires up and runs like a dream. No noise, no miss, semi-smooth idle considering the tranny/engine mounts needs replaced and rev is clean and crisp. Let it get warm and back to the same thing it was originally doing before I figured out the TB was causing all the issues.

Late last night I found out the long starting was due to the FP relay being bad. It had been using the oil pump to fire up the FP. I replaced the relay with a spare that came in a box of parts and the car hits on the first key turn. Except when it's warm now it rough idles, more so than before, and it takes a considerable amount of cranking to get it to fire up. I just don't get this car at all. This is and was my main reason for switching to carb. With carb I can at least rule out a ton of stuff right off the bat since it's so simple. Fuel, Spark, and Air. With this TPI it also needs those 3, however it also needs the 20 other sensors, relays and modules to go with it. I guess an easy way to say it is carbs are alot less forgiving.

I am not giving up just yet. If the car runs good when its cold and rough when hot that tells me the car doesn't like something when it's warmed up. Injectors, EGR or even perhaps one of the new relays, coil or ECM. It's a pin in a haystack type deal.

If anyone has any suggestions on why it would run better cold now and back to rough idle and dead miss I would be happy to entertain it. The last and ONLY thing I have not replaced are the injectors which I have ordered a set of bosch 3's. My current injectors ohm @ 16.2-16.7 cold and hot they are 16.6 to 17.2. I have also verified pulse with a pulse tool. They could just be bad spray or clogged so new injectors couldn't hurt.