Is there a sensor/device that can cause your idle to bounce?

[TruElegance]

I apologize if this has already been covered, but I have a 99 GST and for quite a while I have been experiencing my idle jumping around. It goes anywhere from below 500 rpm to 1000 rpm and I was wondering if there is a sensor or device somewhere that could possibly be bad and causing that. I know the basics about engine management, but Im still learning all the little technical aspects. If anyone could help me out, Id appreciate it.

 

[EuroEclipse]

I apologize if this has already been covered, but I have a 99 GST and for quite a while I have been experiencing my idle jumping around. It goes anywhere from below 500 rpm to 1000 rpm and I was wondering if there is a sensor or device somewhere that could possibly be bad and causing that. I know the basics about engine management, but Im still learning all the little technical aspects. If anyone could help me out, Id appreciate it.

I suffered from the same thing in my 97 GSX for a while. Basically, the things you'll want to test are the coil pack, spark plugs (check the gap), and the Idle Speed Controller (ISC). The ISC is usually the culprit in a bouncy idle. There's a good tech article on "idle surge" that you may be able to find some more helpful information here:

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

 

[wret]

Do a boost leak test.

 

[twocanewayne]

i dont mean to hijack but mine does the same thing after a little boost(3-5)psi but i was told my mods on my fresh rebuilt motor were different than the ecu was set up for.and the surge was it trying to adjust.

 

[twocanewayne]

after reading that i have work to do.

 

[dave99gst]

i dont mean to hijack but mine does the same thing after a little boost(3-5)psi but i was told my mods on my fresh rebuilt motor were different than the ecu was set up for.and the surge was it trying to adjust.

at 3-5 psi your motor is under load and there should be no "bounce"