idling problem on a 1g

my 91 gs has an idling problem it jumps up and down from 2 to 1500 rpms. and ive replaced it with 3 different sensors so what else could make it do this.

check for vacuum leaks that would be a real good start to finding the problem. Maybe even plugs and wires.

vacuum test on what, i was going to change the spark plugs but ran out of money... lol

It could just be that your adjustments are off or that you are adjusting it incorrectly. Remember, there's a CTP switch that needs to be adjusted BEFORE adjusting the TPS. From there you can adjust your idle base settings.

Joel, CA

also check your altanator belt, mine slips when it's loose and runs bad.

do u have an aftermarket bov?

my bad ist a gs nevermind

Does it run rough or does it sound like it's hunting? (Like someone is revving the engine up and down)

you have idle surge. tell us what youve tried to replace to far. Possibilities are a bad isc motor, idle adjustment is off, bad egr, dirty tb, missing/bad vacuume line. no matter what it is, it will be located around the tb

ISC? I'm guessing you mean IAC motor? That was what I was thinking it is...

I would also check the timing... on my car the timing some how got really far advanced and ran like $h!t

Early models used an actual motor actuator to physically move the throttle plate open or closed as a means of adjusting idle- It was called an ISC/MPS or Idle Speed Controller with a Motor Position Sensor. If the setting of the MPS is off- it can cause idle hunting as if someone was stepping on the throttle and letting it go. I have seen many instances where someone turned a screw here or touched an adjustment there throwing EVERYTHING off. It may not need a single thing at this time- it may just need to be adjusted PROPERLY.
Later models used an IAC to control idle with basically allows a controlled amount of air to bypass a fully closed throttle plate.

Joel, CA

Ah O.K. I didn't know they used the ISC on the 1g's my bad.

Not ALL 1G's used the ISC setup- my 93 DOHC has a IAC but i'm not exactly sure what year they started with it.

Joel, CA

I'll browse around through a few books I have and see if I can find something that tells what year and what engine they started the IAC with.