Erratic Idle on Cold Start

[jreese86]

Ok, I searched through the 1st 10 pages of results and I couldn't find any threads with a problem exactly like mine.

I have a 91 Laser RST. When you first start the car up for the day, the RPMs will jump up to 2k, cut back down, jump back up to 2k, cut back down, and repeat. Each time it will take a little longer to get back up to 2k, and eventually it will stop reaching 2k, and slowly wind down to about 1500. At this point I'll usually drive it for a few minutes and the idle will sit at a normal 800-1000rpm during idle. After that, it won't duplicate the problem until it sits for a long period of time, maybe 5 or more hours.

Anybody have any clues on the problem?

 

[RSTurboFWD90]

This sounds like one of the many forms of "idle surge". I recommend you follow the procedures for cleaning your throttle body and ISC and see if that helps.

http://www.dsm.org/how-tos/tttt/tttt3.html

 

[JayRolla]

I have you same exact problem. It happens only when the car is cold and slows down the warmer it gets. Sometimes it does it when warm but not often. Ive done everything to fix it but check the ISC. Im going to replace that and hope it fixes it. Do everything that link says above and it should fix your problem.

 

[silvawolfe]

Same problem here. Checked every thing sprayed starting fluid around and found the throttle body shaft seals are leaking as well as the BISS is worn out. $14 worth of parts and everything peachy!

 

[daren_p]

Im having this issue too, the idle will surge up to about 1400 and drop to slightly under the normal 750. It only does it when its cold & it seems as soon as I touch the gas the idle will return to normal. I replaced the shaft seals this past spring and last time I did a boost leak test (2 weeks ago) there where no leaks. Seems there are a few guys with this issue, anymore solutions?

 

[Dragon TalonTsi]

Check your ECT sensor, Engine Coolant Temperature sensor... or some say CTS, that could be the culprit. I had almost the same problem that you guys are having, and researched around, and sure enough, that is what it was... The ECU sees all the readings from each sensor, and eventhough it may seem small and insignificant, it really does its job. Exactly that, it monitors the Enigne's coolant temp, basically it is to inform the computer of the engine's temperature so that fueling and ignition timing can be modified for all temperature operating modes. It is also used to turn on the radiator fans and also can be used for sensing an engine approaching an overheating condition. When this happens, the computer would open the idle control valve and raise the idle in order to move more coolant through the engine. They have them at AutoZone, Advanced Auto and Napa, etc. I bought a new one, and BAM, initial start up right after, the problem was cured. Like everyone else is saying, double check everything...

 

[JayRolla]

98 eclipse gst check you ISC motor and make sure its working.

 

[91talontsi1505]

You should definately follow the articles for cleaning out the throttle body and your ISC. Something very similar hapenned to my friends 90 gsx and we cleaned them and everything came out fine.