symptom: intermittant high idle.

when coming to a stop it will be between 1000-1500, if you tap the gas it might drop back to normal (750-800).



cause: this is usually caused by carbon build up in the throttle body, although it could be the vent vac solenoids, bac valve the air supply valve, misadjusted throttle cable, or bad thermowax



diagnosis: warm engine to operating temp.



thermowax: it is in the rear of the t body, there is a screw on a spring loaded plunger. you should be able to move it back and forth with no effect on engine speed (when its cold it will, this provides the fast idle) the 86 up thermowax pellet works in a gslse throttle body



throttle cable: it should be looser than you think it should be, about .5-.7" deflection. much less and it will tend to hold the throttle open



air supply valve: this valve is for mainly raising the ilde when the ac is on, or you turn the wheel on a ps car.

it is on the back side of the bac valve on the left side of the intake. unplug the 2 pin connector and jump it to the battery, the idle should go up to 1100-1250rpms.



bac valve: its a vacuum operated plunger, they do tend to carbon up and stick. to test it pull the vacuum line off, with -15psi it should idle normally, at 0 psi it revs to about 3000rpms. i like to clean these out with brake or carb cleaner



vent vac solenoid: these are located right next to the oil filler pipe on top of the engine. they use it to vary the vacuum signal to the bac valve. it is possible that one solenoid is stuck/bad. i find the best diagnosis is to unplug and see if it changes



throttle bodies: they usually are the culprit, either from carbon accumulation or wear of the throttle shaft holes. step one is to gently push down on the tps adjusting screw, when it is idling high. if it drops the tbody is at fault. you need to be very careful with it, as it is very expensive to replace. carefully remove it, and clean the inside with brake cleaner or carb cleaner. make sure the edges of the throttle plates are clean (do not remove the throttle plates they are very difficult to put back in correctly) there is also an idle air bleed port (the screw on top) make sure that is clean too. also if the throttle body hoses have not been replaced you should do so now (N304-13-208, N304-13-209A).



when it is all back together: recheck all your work, reset the tps. the idle speed should be set with the screw on top of the t body.



enjoy

mike

 

so one of these is the problem if my idle is normal but sometimes it will hold at 1200 or surge from 1200 to 1500?

 

yeah, when it does it, push down on the tps adjusting screw, if that fixes it the tb is sticking

 

What if when you start the car is revs to 3k then I have to rev it a few times to get it drop to 1500???

 

bac sticking? its supposed to rev up a bit

 

hey how its going....i am new here and just bought my gsl se about a month ago. i have been having a problem with it idling / running at operating temp, it starts and runs fine until it gets to full operating temp and then sputters and dies.....i have checked the battery, throttle position sensor, AFM, new spark plugs........i am running out of ideas? it runs great when its cold....and idles great when cold. Anybody got any clue of what could cause this.....?????

 

I suggest you run some seafoam on your car, just to clean up the fuel lines and down through the brake booster vacuum hose! Its not gonna fix the problem but will help it run smoother!

 

i have an opposite problem. when the engine is cold it idles really low (say about 0.6k) and is very rough. what would be the cause of this problem?