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derekhay316
09-11-2003, 02:15 AM
I have a slightly rough idle and only when I start my car cold i also have a high idle (goes up to about 2000 rpm) and then when I start moving it'll go back down to normal idle. I've recently replaced the motor mounts, fuel pump and filter, spark plugs and wires. I've heard a lot about the iac going bad? Would this cause the rough idle also? Any input? I'll check my vacuum reading tomorrow. I'm pretty sure its reading pretty normal or slightly off.

jonroe
09-11-2003, 12:41 PM
Mine just started doing this also the last few weeks. When I start cold it wants to die and is rough. Then it gets into a high idle mode for a few minutes until I start driving it. Eventually, it settles down to fairly normal although it seems slower to return to normal idle as I approach a stop.

I'm suspecting the IAC. Any advice out there?

Jon

derekhay316
09-11-2003, 07:31 PM
Ok i just checked my vacuum and when it starts up it goes to about 18 or 19 and then down to 20 where its supposed to be i believe. I don't really care about the high idle on startup, i just want to lose the roughness. I can feel the car shake side to side sometimes when i'm at a stop light. Anyone?

derekhay316
09-13-2003, 11:58 PM
Any ideas?

91BLOWNSC
09-14-2003, 11:59 AM
I would also suspect the IAC. My did the exact same thing when mine went bad. Even when it was cold id started up and idled at around 1800-2100 rpm. I had to get a new one from fords because the one's they sell at aftermarket parts stores is "backwards" and they do not work.

derekhay316
09-14-2003, 02:09 PM
Anyway to clean it or something? I don't have $100 to spend. Would it produce the rough idle also?

91BLOWNSC
09-14-2003, 04:46 PM
Originally posted by derekhay316
Anyway to clean it or something? I don't have $100 to spend. Would it produce the rough idle also?

Yup.....actually they recommended that I try cleaning mine first. I think I used carb cleaner, or something of that nature. It did cure the problem for a short while...nevertheless it came back and I had to replace it. Just take it off and clean it with that and a cue-tip is what i used I think. Be careful poking around inside tho.

derekhay316
09-15-2003, 12:23 PM
Ok I'll try er out.

BobGPz
09-15-2003, 07:49 PM
:eek:

DON'T CLEAN THE IAC!!

If it is bad, then it is bad. Just deal with it until you get a new one, but don't clean it out.

Me and another guy have both had large posts chasing down the problem with an IAC and we both had recently cleaned them out. You'll have nothing but probs after cleaning out the IAC.

Hope I caught you in time.....

Edit...Here is link to 6 page post trying to figure out after he cleaned out IAC, My post was longer... :p http://www.sccoa.com/forums/showthread.php?s=&threadid=28866&highlight=IAC

derekhay316
09-15-2003, 09:05 PM
OK I sprayed some carb cleaner in there so i guess its screwed eh? I guess I'll just have to replace it. Any ideas what would be the cause of the rough idle then? I did a KOER test and came up with code 98: Computer detected hard fault (EEC in FMEM or Failure Management Effects Mode)

Any ideas?

nitrouspaul
09-15-2003, 09:23 PM
I need an IAC anybody got one in the toronto area.

BobGPz
09-16-2003, 07:23 PM
Put it on and see if it is worse than before. May be lucky and it is not the IAC. But these were obviously not made to be cleaned or so many of us wouldn't be having problems with them after cleaning them out. I wonder if the diaphram gets eaten away with the brake/carb cleaner. Hmmm?

How high is the idle? Any strong fuel smell or anything? Glowing headers? What is your vacuum guage saying at idle and what rpms?

MIKE 38sc
09-16-2003, 08:03 PM
Yes Bob the cleaner makes the plastic acordian boot hard and brittle, it then just crumbles and falls apart.
The only thing I would even think about using is Fuel Injection Throttlebody cleaner, its a completely different chemical and is supposed to safe on plastics and electronic sensors.
Unless the inlet or outlet holes are completely stopped up then do not clean it. There is nothing to be gained by cleaning it internaly.:)

derekhay316
09-17-2003, 02:13 AM
Ok after cleaning out the IAC nothing seems to be different. It still revs up to 2100 rpms when the engine is started any time, and then slowly goes back down and is normal the rest of the time. At idle the boost gauge is at 19 or 18, but when I tap the gas it usually settles down to 20. Could the cause of the rough idle perhaps be the tranny mount? Just one thing i haven't changed while i've owned the car.

MIKE 38sc
09-17-2003, 01:23 PM
Could the cause of the rough idle perhaps be the tranny mount? Just one thing i haven't changed while i've owned the car.No.

At idle the boost gauge is at 19 or 18, but when I tap the gas it usually settles down to 20. Sounds like the IAC is lazy in reaction. You probably just need a new one. Those things can fail in several different ways.

It still revs up to 2100 rpms when the engine is started any time, and then slowly goes back down and is normal the rest of the timeThats what I mean by lazy reaction. The mechanical part of the IAC may be in a bind causing this.

derekhay316
09-17-2003, 01:43 PM
Ok thanks. I'll get a new iac pronto.

BobGPz
09-17-2003, 03:12 PM
Go with a new IAC.

BTW, Have you disconnected your battery lately?? Maybe comp is just relearning idle. Doubtful, but just a thought.

derekhay316
09-17-2003, 05:48 PM
Yeah I changed the battery cables about 2 weeks ago.

BobGPz
09-18-2003, 08:43 AM
OK, did this problem arise BEFORE you disconnected battery? If so, then I'd say your IAC could be toast. If NOT, then it is just your computer re-learning the idle which is done each time it looses power to the memory (When you disconnect the battery). Just takes a few days for computer to get smart. Best way is to just start it up and not touch gas pedal for 10 minutes after a disconnection.

derekhay316
09-18-2003, 10:08 AM
Ok I'll try that out. Thanks.

fastscbird
09-22-2003, 02:12 PM
what is a iac

jonroe
09-23-2003, 05:05 AM
The IAC is the Idle Air Controller. It is a unit sitting on the side of the throttle body which passes a small amount of intake air around the throttle body butterfly valve at the proper amount so that the engine will idle at the proper speed. They can get dirty and/or stick to cause idle speed problems.