car is acting wierd at idle. please help

[1gDsmRacer92]

ok heres the deal. about a week ago my car started acting wierd at idle, it drives fine when you hit the gas it hauls ass and sounds good, but at idle after its warmed up it acts like its missing, it doesnt stall or run rough really but if you sit and listen to it it sounds like the motor just stop but it keeps going, and the idle pulses also from about 800 rpm to 1000, does anyone have a clue what it could be, the plugs and wires only have about 10,000 miles on em and the fuel fitler was just changed, air filter is clean. and by the way the new CAI i got from 2kracing.com is awesome and it was only $99 shipped its a true CAI not a short one. but any help would be awesome thanks.

 

[dr1665]

Might be your IAC. They can get tired or dirty over time and start to give you a screwy idle. Mine is toast and she will hang around 2000rpm until I come to a complete stop. They are also known to have the o-ring that seals the actuator in the TB rot away and allow air to sneak past, causing idle issues. The hardest part about inspecting/cleaning/replacing the IAC is getting it off the TB for the first time. It uses Torx screws which are Loc-tited in place. Not uncommon to strip them or break a head off.

Then again, you might want to check the gap on your plugs. It could be anything, really. :shrug

 

[1gDsmRacer92]

hey whats is the IAC i think that may be my problem cuz it does idle a little high till i come to a complete stop so im thinking thats it, thanks man. also where is the IAC located (if its on the throttle body were at on it, sorry man im still learning were everythings at on the 420a motors.

 

[99 eclipse]

Idle Air Control motor. its located on the throttle body

 

[Project Draven]

Pull off your air intake tube from the TB, You will see a lil hole on the bottom. Thats where the IAC sits. Looking at the TB, you will see 2 clips that connect to it. The IAC is the lower of the two.

Hope that makes sense.

 

[Doug99RS]

Any check engine light codes? Most of the time if it's an IAC motor then the idle will flare up or drop down real low. In addition to that a failing IAC won't affect the engine giving it a mis-fire like condition. Remeber the IAC only controls air entering the plenum and does not affect air/fuel ratio which is one of the main things that contribute to mis-fires. The TPS on the other hand is also something to consider since it determines throttle position and dictatates which fuel map the PCM should use. But this is simply one of the many sensors that COULD be causing this condition and without a code or some sensor readings while it's acting up it could be any number of things.

At idle the o2 is playing a significant factor in air/fuel ratio. The EGR valve could be sticking open causing mis-fire like conditions and poor idle, and even a bad thermostat or coolant temp sensor could be at fault.

There's alot of people on here that know what can contribute to your condition but we're useless without some more specific info to rule out some items.
Doug

 

[1gDsmRacer92]

ok i found were its out you guys helped alot, im prety sure it is the IAC beacause ive clean out my throttle body many times with stp throttle body cleaner and im sure alot of the nasty black oil residue fell down in the hole so ill either clean it out or replace it this weakend when i put my ported throttle body on

 

[nelapse]

Do not take your TPS out of the equation.. they all work in conjuction. TPS connector gets dirty those are symptoms.

 

[95 'clipse RS]

mine was actually a bad intake manifold gasket, it had a couple cracks creating passages for more air than needed at idle, if the iac valve cleanout don't help...

try testing the airflow bypassing through the tb through the iac, if its not too strong there could be a leak...

then try squirting a stream of water along the intake manifold, where it meets the block, if its there the cars idle will vary alot then return and you'll see and heat the water being sucked in.

 

[Doug99RS]

I would not recomend using water. Use carb cleaner/ throttle body cleaner. It's at least a fuel and will combust or simply foul out a plug if all of it does not ignite. Water will not burn on even the best of days and may hydrolock the engine. Good call though on checking for vacuum leaks.
Doug