cold start, idle jumps

[SloCelica]

I read the recent thread on idle surge, but it didn't sound exactly like my problem. I've also searched and found similar threads directed to 2nd gens, but didn't know if it would solve my problem.

Basically, I just bought a 1991 Talon TSI, FWD 5 speed. The car has one problem sticking out...the idle will surge up and down until it reaches operating temperature, and then it is fine....idles and runs perfectly. My question is, where should I start to find the source of this. I'm a 4g63 newbie, but my mechanical skills are decent enough to fix minor problems. Any help would be great...I'm assuming to start with the BISS, and see if its leaking? Thanks in advance.

 

[AJGoldie]

I had this problem as well but never exactly pinpointed the problem...tried replacing the ISC, adjusting the BISS, replacing ECU...

 

[snailed]

its probably the Fast Idle Air valve. its directly under the throttle body and is incharge of speeding the idle up in cold starts and lowering it back down when the coolant temps are at normal operating temperature. could also be what he described above or a vaccume leak somewhere. well good luck.

 

[SloCelica]

Thanks, Snailed. That makes a lot of sense to me, seeing as the closest thing I could think of to compare it to is a problem I've seen with the Fast Idle Thermo Valve on an Acura Integra. Same principal. I'll see if its just sticking or if it needs replaced. thanks again for pointing me in the right direction.

 

[King Salami]

If you've got a Haynes shop manual for the car (if not, get one - it's the best $13 you'll spend if you plan on wrenching on the car yourself) you can use a multimeter to test the ISC coils to make sure all have continuity. An ISC with burned out coils can cause this as well as a FIAV.
You may also want to try Mopar Combustion Chamber Cleaner. Go to www.vfaq.com and look up idle surge.

 

[SloCelica]

Big help, thanks a lot. I'll give all of this stuff a try over the weekend and see what happens. I appreciate all the help. I'm gonna go check ebay for a haynes manual