Crazy Idle...Like nothing I've experienced

[TurboDreamzGST]

Hey guys...got a 98 GST, intake, evoIII 16g turbo, megan racing o2 housing, 3" custom cat-back exhaust, greddy type RS bov re-circulated...i just started experiencing this weird idle problem...i know the first thing everyone is going to say is do a boost leak test and this is my 3rd DSM so i know the headaches that boost leaks can cause but ive done several tests and came up with nothing. My problem is that when I first start my car when it's cold, the idle is very rough and low...usually around 500-600...after driving the car to work (about a 35 minute drive) or after the car fully warms up and runs for a about a half an hour or so, the idle raises up to anywhere around 1000-1300 and stays there. Its so weird and I have no idea what's going on. By the way, I'm throwing no check engine lights and i used a code scanner just to make sure and nothing at all comes up. Now someone had mentioned that since i blew my t-25, i'd probably have to clean out my throttle body because all the oil that passed through it may be "gunking" up my throttle plate so I opened up my throttle body and cleaned it all out. Although it was dirty, it wasn't horrible at all. I put some new gaskets on it and put it all back together with still the same results. Any ideas at all as to what this could be or what I can do to fix it would be very much appreciated. Thanks guys!

P.S. I forgot to mention that I did a full tune up only about a month and a half ago with new plugs, wires, fuel filter, new intake, and pcv valve and the car ran great up until about a week or 2 ago.

 

[nyTalonTsi]

Well with a t/b carbon or oil track, a clean up will help that idle out alot. Have you checked your ISC and BISS screw?

 

[TurboDreamzGST]

what else would i have to clean up if i already cleaned out the throttle body? all the intercooler pipes and intercooler? i checked the pipes and dont see much oil residue in them to be honest....and no I havent checked the ISC or BISS because if that were the problem, wouldnt that have been happening since i got the car due to the previous owner messing with it? and wouldnt that cause the idle to be messed up all the time?

 

[stevestevesteve]

mines at 150 rpm's and now its getting lower. i took her out for a drive today to the bank and when i got back to my car, started it up. she jumped to 1000, then dipped do to 50! ya 50, then rose to 150 then whent back down to 100

 

[audiomaster1990]

get a new idle speed control motor.

yours is old as hell, and probably goin out. mine started to crap out and it did that everyday.

its sad that nobody else on this site knows a damn thing about dsm motors or that would be the first response youd have gotten.

 

[TurboDreamzGST]

I also forgot to mention that it seems like when it's cooler n the air outside is moist the idle stays lower longer n when it's hot or dry the idle is higher...could this help anymore to diagnose my problem? And also if my idle air control was bad wouldn't I b throwing a CEL?

 

[turbotsi92]

I agree with the ISC comment. I am having the same issues right now, just no funds to get another one. My car does basically the same thing, but more all over the board than what you are saying.

 

[TurboDreamzGST]

Is the idle speed control motor the same thing as an idle air control motor? Just 2 different names?

 

[GTOJohnny67]

I don't know if this will help you or not. When I first got my car it would idle at 800 and then as it warmed up it would rise all the way to 2000 some times. Turns out my throttle cable was shrinking as it got hot and holding open the throttle a little. There is an adjustable bracket on the back of the intake manifold I loosened it up and while the motor was hot, and made sure the throttle was closing all the way. It only moved the bracket a hair but it fixed my idle problem. Might be worth looking at.

 

[TurboDreamzGST]

I never thought about the throttle cabel...I'll check that out. But is the idle speed control motor the same as the idle air control motor?

 

[crimsondragon]

My guess is the FIAV is not working properly. Pop out the freeze plug on it and close the valve.