Rough Idle on Cold Starts

[BestBuy297]

I just bought my 99 GST on Saturday with 65K original miles on it. The dealer I bought it from told me that they just replaced the idle sensor, because it had a cold rough start. Problem is, it's still there. Dealer said they couldn't figure it out. It takes a couple of minutes for the idle to smooth itself out. Before that, it seems like it wants to cut off, the idle drops down to like 700 or so.
I am complete newb to turbo'd cars. Came over to the DSM side from the Hyundai crowd, and I only have N/A tuning experience.
I can't go back to the dealer, since I live in Northern Va and the dealer is in Deleware, don't wanna make that trip again
Anyone know where I can start looking for the problem at?

 

[95blackGsTurbo]

There is a Hyundai crowd? Anyways. Does it just idle rough or does the idle bounce. Does it stop once the coolant temp. get's up to operating temp? Or does is smooth out before then. It should idle around 750. Cold it should be bumped up a bit. Start by checking the plugs of course. Then check the wire's for breaking or fraying. If it only does it when the car is cold, try checking your Fast Idle Air Valve.

 

[BestBuy297]

Definately bounces. Idle smooths out prior to coolant warming up. Plugs are new, wires are not. So, I'll check that and the fast idle valve. When I check the FIV, what kind of damage exactly am I looking for?
Thanks for the reply

 

[andymoraitis]

If they replaced the ISC, I would still remove it (don't lose the o-ring) and leave it plugged in while you turn the car to ignition (don't crank). If the stepper motor moves, it's OK. As far as the idle bounce check for little things first like a missing o-ring for the BISS screw on top of the throttle body.

As an FYI, the FIAV will control idle until the coolant temp reaches 122 degrees and then idle control is turned over to the ISC. If the bouncing is happening while the motor's dead cold, I'd suspect either a BISS o-ring leak or the FIAV. Unfortunately, the FIAV isn't a cheap part and can run you upwards of $150.00.

 

[95blackGsTurbo]

Thanks for that Andy. I couldn't remember what the temp. was for the FIAV to shutodown. Good idea with also checking the BISS o-ring.

 

[Eclipse98_RS]

I have the same problem (98 GS-T) except my car only does it when its cold outside. On warm days it squeeks for about 2 seconds and then its fine. I have a frayed power steering/alternator belt and im thinking thats the culperit. Am I correct here? I had my BISS checked out around a month and a half ago and it was fine.