85 911 3.2 idle problem

[mr914]

Good Day,

I recently reinstalled my motor and trans back in my 85 911 after replacing a clutch. The car now has developed a weird idle problem that I am having trouble trying to figure out.

Whats going on is, if I go above 2000 RPM the engine seems to want to idle at 2000 rpm. If I let out the clutch a little and drag the rpm down below 1900 it will idle down to about 900 rpm until the next time.

When it is idling at 2000 rpm, it has enough air flow to move the car at in any given gear.

While the engine was out, I did replace the bushings for the throttle pivot on the trans, cleaned the ISV, throttle body and air flow sensor with carb cleaner. I'm pretty sure it is not a linkage issue, when Idling at 2000 rpm, I've opened up the engine compartment and made sure the throttle body is coming closed.

Could it be a vacuum leak? In my mind if it was, I would have the idle problem all of the time.

Any thoughts?

BTW - At startup, it fires up after cranking about 10 seconds and idles at 900-1100 RPM and it occurs once the car is semi-warm to warmed up.

[Zeke]

When this question comes up, many say check the flywheel sensors and head temp sender. Do you know that those are all OK and properly adjusted? I really don't know, just passing the word along.

[steely]

Based solely on my own limited experience, faulty CHT and flywheel sensors led only to complete shutdown as opposed to floating idle rates, but maybe I had a different combo of conditions.

Can you check the throttle position switch continuity (should be infinite/short) and the Air Flow path resistance (should vary with position) at the connectors? Good luck.

[kidrock]

maybe sticking linkage in that area around the tranny bell housing?

[dshepp806]

idle switch activating? (measured?)

Doyle

[Steve W]

It sounds like the throttle linkage is too tight, preventing full return of the throttle, thus not activating the idle position switch. If not that, then the idle switch is either sticking or needs to be adjusted so it consistently activates - use a test meter to check.

[mr914]

CHT was checked when motor was out and was found to be the updated sensor and within specs.

As far as the flyweel sensors, I unbolted them and rebolted them on upon reassembly. I was not aware that there was a clearance dimension.

The bushings were replaced for the pivot on the transmission.

When idling @ 2000 rpm. Opened engine compartment and tried to move the linkage further closed. No change in idle speed

Whats odd is that if I let the cluch out a little bit to pull the idle down, it returns to normal idle.

[mr914]

I checked the throttle position switch and it appears to be working fine.

I have not checked the Air Flow path resistance at the connectors yet. Will check tomorrow night.

[kidrock]

There is a clearance setting for the flywheel sensors, if I were near my Bentley I would give them to you. The correct clearance is crucial to a correctly operating vehicle.

[Zeke]

It's about the thickness of a business card. But, I think they have to be pretty far off to have drastic effects.