ercando

My new to me 1987 911 has a very annoying habit of not idling down. When I lift my foot at a red light the idle can be 2,100,-1,200 and sometimes the correct 950. If I press on the throttle plate linkage where the cruise cable attaches it will idle down. But I'm literally only moving the throttle plate linkage a micron. Any suggestions would be helpful. Thank you.

76FJ55

check and make sure the idle switch is adjusted and making contact when the throttle plate closes to the idle position. that last little bit you push it may finally get the switch to close.

If that doesn't fix the issue the 3.2 engines are prone to vacuum leaks especially where the intake mounts to the heads due to the plastic isolators/spacers installed with upper and lower gaskets. Any vacuum leaks will cause issues with idle.

ercando

Hello. You were exactly correct! With the car off, when I push the throttle down I can hear the idle position microswitch click! Thank you for the response. How do I adjust this? The Bentley book I have doesn't do a good job explaining the adjustment process.

76FJ55

I'd start by disconnecting the throttle linkage at the TB and see if the switch closes when you open and release the throttle. it could be that the linkage from the pedal needs adjustment and not the switch itself. if the switch closes without the linkage connected adjust the linkage accordingly.. if it still doesn't make contact then work on adjusting the switch. It's been a while since I've looked at it, but if I remember correctly there are 2 small flat head screws that secure the switch. once you loosen these the switch can be move around to achieve the necessary position. The Bentley manual covers the throttle position switches starting on page 240-18. you may have to remove the throttle body to access the idle switch.

ercando

Upon further investigation today I discovered that my idle air control valve is frozen shut. I have a new one ordered, hopefully its not NLA. I'm now wondering with that valve being frozen almost completely shut, could this have been creating a vacuum that was causing my throttle plate to hang up? I guess I'll find out with installing the new one (hopefully). Or would these two issues be completely unrelated? Thank you again for your very helpful suggestions. I just acquired the car and this is the one issue that's been a real nuisance.

76FJ55

It is possible for the idle control valve to fail. It seems unlikely to me that being stuck closed would cause your current issue. If it were stuck. Loved it would seem to me that your idle would be lower than normal instead of high.
if it is just sticking, but the electrical is still working, you can flush a much of carb or electrical cleaner through it to help free up the armature.
if the TB isn't closing enough to trip the idle switch I'd start by disconnect the linkage and check to see if that corrects the issue. If it does, then focus on linkage adjustment. If disconnecting the linkage doesn't resolve it, the investigate the TB and switch adjustment. All of this is done without the engine running so needs to be fully functional before ever worrying about the ICV.