What can cause Rought Idle????

[93octane]

My 99GT has a rought idle not too bad. I swap the spark plugs with some autolites 764 gapped at .54. It idles the same but now after I turn it on I let warm up for about 2 min. drive down the block and when I get to the stop it sorta wants to turn off but it doesn't. It runs fines..it pulls hard, & no problem with the car lighting up the tires. Its just when I get to the stop it doesn't idle too very smooth and it feels like it wants to turn off but it doesn't. Any ideas???? The car is Bone stock with 43K miles. Just changed out the fuel filter,pvc valve and spark plugs????

 

[twogts4us]

Could be a few other things, but looks like you checked the obvious - fuel filter, PCV, plugs. Check all vacuum lines. Check the EGR valve. Changed the air filter lately? What other mods do you have and when did this rough idle start?
Welcome to StangNet!!!

 

[madmatt]

Try cleaning your IAC. That is what seems to cause most idle problems in our cars.

 

[streetstang03]

Try cleaning your IAC. That is what seems to cause most idle problems in our cars.

most likely your IAC, especially if it is dropping RPMs when you get on it or give it some gas.

 

[93octane]

Where is the IAC??? How do I remove it..And how do I clean it thanks.

 

[Z28 KILR]

Where is the IAC??? How do I remove it..And how do I clean it thanks.

I wish I could find a picture but I cannot seem to be able to but the IAC is the pastic piece of the front of the intake. Can anyone else help?

 

[new22003]

IAC is the most common it is attached to your throttle body with 2 bolts and has a hose running to it.

 

[jmichalicek]

http://www.muscularmustangs.com/iac.html

 

[Red mustang Gt 46]

As stated many times before...replace it...49.99 at Auto Zone...

 

[93octane]

What can I clean the IAC with???? Carbcleaner??? Will it hurt the electronics???

 

[jmichalicek]

Yep, carb cleaner will do the trick. I Just spray into the holes and shake it around a bit... maybe use a wire brush to scrub it some.

As said above, cleaning is just a temp fix. In the end you really will need to replace it.

 

[new22003]

I would replace it but if you clean it use carb cleaner. You still have to remove it to clean it. There is also a gasket so make sure its in good condition if you dont have a replacement. It is a 5 minute job to remove and replace.

 

[UNVMATT]

I have this idle problem too. My IAC went bad last year and the car wouldnt idle at all. I had to rev the engine just to keep it running and the motor sounded flat. Changing the IAC fixed the problem. 42.99 at NAPA.

Also my car developed a funky idle in which eventually led to the check engine light coming on. I had it checked out and 2 ignition coils went bad. Im not sure if the dummy light comes on if 1 was bad or not but I know if 2 go bad then it will light up!

The idle problem still exists despite changing PCV, cleaning air filter, new plugs, etc. Sometimes my car will even shut off after driving then pushing the clutch and braking. Which can get hard to control since the power brakes and power steering dont function as great.

I know many people have this problem but Ive never heard what the cause was yet.

 

[Turbo92PGT]

I dont have the COP's but I think my Coil packs are bad. My car does not idle smooth at all. I have done 2-3 sets of plugs, replaced wires, bought a new IAC, fuel filter, PCV, fuel injector cleaner, Sprayed some carb cleaner in the t/b. Used electronics cleaner on all the connectors around the engine bay. Cleaned the MAF out, IAT, etc. Still idles crappy. It pisses me off. My code reader has said "multiple cylinder misfire" pending. Think the coil packs are bad? I think im gonna go with screamin demon's. I would go with MSD's but I cant find them anywhere

 

[Red mustang Gt 46]

I dont have the COP's but I think my Coil packs are bad. My car does not idle smooth at all. I have done 2-3 sets of plugs, replaced wires, bought a new IAC, fuel filter, PCV, fuel injector cleaner, Sprayed some carb cleaner in the t/b. Used electronics cleaner on all the connectors around the engine bay. Cleaned the MAF out, IAT, etc. Still idles crappy. It pisses me off. My code reader has said "multiple cylinder misfire" pending. Think the coil packs are bad? I think im gonna go with screamin demon's. I would go with MSD's but I cant find them anywhere

Your, probably correct about the coil packs...Summit racing had MSD's or Accells, both do the job. Do you have the wires routed the same as the stock configuration? (over the alternator)

 

[thebeastum]

i had the same problem after i changed my pluggs, and fixed it by cleaning out my iac and all found that my intake tube clamp was wouldnt keep tight and the tube would repeatly loosen and fall off.

 

[Wi-Stanger]

The IAC is the thing that connects to a hose and empty plastic box right in front of the horse on the 99+ GT right? I took that off and sprayed it but I didn't see any gasket? What's my deal?

 

[scooter6753]

yes on the 99=gt it is actually made of metal and is infront of the horse...it should have a gray gasket...will a dirty clogged old air filter severly affect my low end pickup?

 

[00VERT GT]

another rough idler here. Changed IAC twice, new maf checked everything else can't find solution. sucks. sucks bad