1992 S-10 2.8L V6 Idle Craziness

[DaleReynolds24]

Hello. I have a 1992 Chevrolet S-10 pickup with the 2.8L V6. Whenever I start it up, it immediately dies. Sometimes I have to hold the starter and push on the gas to get it to turn over. Once I keep on the gas it fires up. But I let go of the gas and it wants to die.

However when it runs for about a minute, then the idle is very high. I have a manual transmission so everytime I push in the clutch at a stop light, the idle goes very high until I put it in gear and it runs fine. It runs fine when I'm on the gas, except for a buking feeling under acceleration where the truck is not getting power. Then I'll park it and take it out of gear and the idle comes down after about 20-30 seconds and it wants to stall (its pratically at about 400-500 RPM, chugging), then it idles normal again after letting it chug, then it wants to die again. I smell raw fuel so obviously it's not getting fully burnt.

I believe this is a Mass Air Flow issue, or even a Idle Air Control issue. The plugs are under 10,000 miles, a fuel pump issue would not have me smelling the raw fuel, and the compression is fine (the engine only has 66,xxx miles). Can any expert give me an opinion on what this is? Thank you.

[Nychao]

That really sounds like an issue with the IAC. Try unpluging your MAF sensor. If it dies, your problem is further up stream. But i'm almost certian its the IAC.

[DaleReynolds24]

Alright so I just yanked the vaccum line to the MAP sensor off and it died out. Further up stream? Maybe the IAC?

[Nychao]

Yeah check the IAC. The IAC controls... well The idle. At first start up, during deceleration and while under heavy breaking. It will allow more air to bypass in the the engine to help warm up the vehicle, to maintain the idle while decelerating because of the loss in vaccum and also loss of vaccum while under braking because your brake booster steals so much vaccum. Thats why it rev's ups like crazy and wants to die all the time. The IAC is not opening and/or closing properly. Do you have a manual for that truck?

[DaleReynolds24]

I unfortunately do not have the manual for the truck. I replaced the MAP vaccuum line because I snapped that off. I am willing to do the IAC myself, I just want to have a guide on where it is and how to do it. I know IAC's can get clogged up, or the motor can die out. I do not know which one of those it is. I wish I had Mitchell On Demand like I did at school lol

The good part is that she runs absolutely flawlessly when I'm on the gas and going. No knocking or ticking, purrs like a kitty. Obviously its the IAC haha

[wlfee69]

Hey, My problem was/is similar... Though my problem wasn't a stall issue, I am certain I know why yours may be dying/missing at startup...

I started by replacing the "throttle body gasket" which was leaking. This did help, but not a whole lot. Second, I took out the "iac" valve located on right side of throttle body (big round cylinder with grey plug)and sprayed the crap out of it with carb cleaner. I also cleaned the port that it fits into. This helped dramatically, but sadly, temporarily...

By now I am starting to get pissed. So, I pull out the pcv valve by snapping the CHEAP plastic line, replace it with "fuel" line, and replace valve. Still no results.

Then I happen to notice a module in between the coil and distributor.
It has little fins on it and 2 vacuum line goto it. on the firewall side there is a round cap on this module. Under cap a filter.

Popped it off and cleaned filter with dish liquid, and dried and replaced. Guess what??? Perfect IDLE!!!

If you are not sure to put this filter back on correctly, it will run like crap, miss, exaust will smell of fuel, and have poor accleration.

Try taking the filter off then start it. It should initially idle high then steadily drop to around 550 to 800 rpm (standard tranny idle is always a bit higher then automatic idle, so I am told.)

Hope this helps you...

[DaleReynolds24]

I have fixed the issue! BUT it wasn't what I expected!

I went ahead and I took out the IAC motor and replaced it. I checked the IAC motor by leaving it plugged in. I turned the key on (didnt start the motor) and the little sprint didnt even so much as budge! It wasn't giving off a diagnostic code so maybe the sprint was just not working or something. Went to the local Advance AutoParts and got a new one.

We put it on and it helped...but the truck still didnt sound good. Until I did some more searching and I came across what I BELIEVE is the EGR valve. Its a silver diaphram-looking thing almost completely behind the throttle body. It was CLOSED (the diaphram was pushed upwards).

I know that these are known to fail (and especially on my truck with only 66,000 miles, everything is original and 18 years old) so I took a little screwdriver and popped the diaphram back open and WIOLA! Purrs like a kitty.

The IAC was not totally misfounded because on inital startup, it was a hell of a lot better. But just for kicks I decided to clean the crap out of that valve to make sure it wasnt clogged up.

Not bad for a 19 year old, working on a truck that easily could be the age of his best friend (or girlfriend!) This Automotive student DID learn some things last year, and now hes a happy camper lol