IAC testing

DZGunner · 10:47 PM

Hey guys its me again. if you saw my other post i had the leaking transmission, which i just took in to get fixed... sort of, its leaking again so I'm gonna have to have the guy do it again.

anyways... I've had the car running, as in moving and driving around pretty well for a while. but i still have the idle issues, as in i come to a red light or stop sign and must always have my foot slightly on the gas to keep the car alive, if i don't it will run into a really rough idle and die very fast. especially if the car has been driving and is warmed up it will die really fast if i don't have my foot on the gas.

the PO told me it was the IAC that needed to be replaced. and i decided I'm going to be doing this one with my dad, not going through a mechanic or anything. so my first task is to get to it, so far we have the fuel lines drained and injectors are all pulled, tomorrow we will take the intake distributor off so i can get to the part under it.

what i need to know is once i get to the IAC is there a way for me to test it without ordering another one. I've read in places that this idle issue is caused by everything from the MAF to the throttle body to the IAC, or even just air getting in past the MAF and making a rich mixture.

SIDE NOTE: when i had the car taken in to get the tranny leak fixed, i asked the guy to look at the engine and to tell me why it sounds really rough and idles horribly. he said there is a misfiring cylinder, and that it has good compression, so that leaves spark plugs and or the rich mixture that i may have to not let the cylinder fire. so for all i know this could all be stemming from one problem, any ideas?

Mrmerlin · 08-10-2012, 10:05 PM

what year is your car?

DZGunner · 08-10-2012, 10:19 PM

1987 s4

jstobo · 08-11-2012, 05:39 AM

Pull the injectors and have them cleaned first. If it was the MAF it would be really hard to start and would run very rich with black smoke out the tailpipe.(limp home mode). It could be the idle controller but if you have dirty injectors it will not solve the problem. The liquid injector cleaners do not work if the car has been sitting. I went through all this with my 85. Once you have the injectors cleaned then if it still doesn't idle you can start working on other potential causes. If you look at the troubleshooting guide in the WSM, one of the causes of all the poor running issues is injectors. The cost of having the injectors cleaned is about the same as an idle controller.

Niles · Niles's Garage

If you have unmetered air leaking in after the MAF (Mass Air Flow sensor), this would cause a lean condition. When my MAF was bad, the symptom I was having was difficult warm starts and the after warming up the idle speed was cycling from normal to slow and back. It was very rhythmic. I talked to Roger at 928sRus. He recommended I disconnect the MAF to see how it ran. The cycling idle immediately leveled out. I purchased a rebuilt MAF through him and all was well.

I am currently suffering issues very similar to yours. When hot, the engine idle speed drops off to where it wants to quit. My gas mileage has decreased. I suspect it is running rich now. I recently did the intake refresh with reconditioned injectors, so I don't think dirty injectors are my issue. I am really curious to find out what solves your issue.

If you are not familiar with Dwayne's Garage (Dwayne's Garage), it is a great reference. He had detailed instructions on an intake refresh for an 87 which will include how to remove the fuel rails and intake.

waynestrutt · 08-11-2012, 11:06 AM

Check the flex plates for distortion.TBF warning is stalling when warm and at idle.

DZGunner · 08-11-2012, 12:50 PM

I guess i should mention a few more things...

The PO said he cleaned the injectors, so i'll take his word for it. however when the engine is running there is a massive hissing sound. i've already checked the easy to get to vacuum hoses and fixed a few vacuum leaks, but still the idle is bad, and still it hisses. so idk if its a vacuum leak or a bad gasket somewhere on the intake distributor. unless someone can verify that all 928 s4 engines make a distinct hissing sound, i'd say i have air entering somewhere and passing the MAF most likely.

i should also mention i was having coolant leak from the upper radiator hose right at the part where it connects, due to the ****ty paint job the guy did, he left a glob of paint on the part that should be sealed. i solved this issue but it leads me to believe there could be similar issues, just with the intake.

DZGunner · 08-12-2012, 12:39 AM

Alright, so i managed to get the intake manifold/distributor off after a while, and my problem became really obvious... This is a hose connected to the IAC, so it sort of makes sense as to why my idle is really bad. It's also coming from the area i posted about before where i originally heard it from.

Also i found that once i took the side covers off the intake manifold, there was alot of oil inside, and after reading about this i decided to pick up one of these to help stop this... Oil Control Baffle.

Also after comparing what i have with the Porsche diagrams i have, it seems like i might be missing a mesh cover on the bottom of my MAF? If anyone could tell me if this is important or not i'd appreciate it, otherwise i dont think i'm gonna worry about it.

stepson · 08-12-2012, 06:26 PM

Bottom mesh on the MAF is not nearly as important as top mesh

DZGunner · 08-13-2012, 01:26 PM

k, thanks stepson. what ever happened to those wheel wells huh? also, do you have the intake tubes? mine have little holes from mice that apparently were living in the engine.

stepson · 08-13-2012, 08:18 PM

Yes, I have some, but you will want to buy new. Do it one time right and be done with it. No sense putting in used stuff that may cause you to redo your work in 6 months or a year.

DZGunner · 08-20-2012, 01:14 AM

Alright, i got it all put together a few days ago, and have been driving it alot actually, almost everything is perfect now. I ended up buying a new IAC (recommended by PO when i bought it) and i replaced the damaged hose. I also replaced alot of other old hoses that seemed they needed to be fixed. I even managed to correct a few mistakes the PO made when he had the intake off (vacuum ports left open and tubing put on incorrectly, as in wrong fitting ends). after hours of work with my dad its able to run like a normal car now.

the only thing now is that when i first start the car after it being idle for a long time (or just over night) the car will still have a jumpy idle, especially when i try to reverse out of the garage it likes to jump alot. I've kinda just learned to deal with it, but if anyone has any ideas i'd be open for what you think. other than that the car runs fine once it's warmed up.

If it makes anyone feel good, i also put a 2006 or higher (they all look the same) corvette to shame today. i came up behind him pretty fast, which made him feel a bit froggy i guess, so he tried to lose me, nope, kept on him till i passed him at 120, and he couldnt keep speed through the turn we came up to, i laughed.