High idle after valve adjustment
 

Car is a 1978 911 SC

What has been done since running ok:
- Oil + Oil filter
- New belt
- Valve adjustment

I finished my first valve adjustment today and now the car idles strong cold (+- 1200 RPM) where it used to hunt at idle before the adjustment. However when it warms up, the idle increases accordingly (After 5 min. driving, +- 2000 RPM) and the decelaration is very slow.

Can this be caused by a bad valve adjustment? I verified vacuum hoses, electrical connections etc. but couldn't find anything... Any idea's?

Its my opinion that your increase in idle is not due to the value adjustment.
Hopefully someone who's familiar with a 78 SC will chime in on possible causes.

When i bought my '73.5, the valves had not been adjusted for awhile and were all tight (normal wear).....After I adjusted, my idle went up, hot and cold....I wrote it off to running more efficiently and losing a little compression when tight. Were your valves on the tight side when you checked them?

Check that your warm up regulator has power when the engine is running.
The fuses are in the engine bay panel near the ignition system on the left side.

If it does have power it's difficult to check it's properly functioning without the right test equipment.
Maybe take it to a Mechanic who knows the CIS system in your car.

I'm betting you accidentally disconnected the power wire to the regulator when you were doing your valve adjust. It's easy to do.

Your comment, "...and the decelaration is very slow." may be a clue. It sounds like you developed an air leak somewhere even though you already checked all the hoses. Try removing the oil filler cap and see if the idle drops. If not, likely an air leak. Check closely the decel valve hoses. Try adjustment of the idle screw in the throttle body--if you cannot adjust down the idle with the screw, you've likely got an air leak somewhere.

edit: Peter posted while I was typing and made a great point. The connection to the wur also supplies the auxiliary air regulator which allow extra air during warm up. If it fails to close, you'll get high idle. Also, failure of the auxiliary air valve which is not dependent on warming but rather vacuum, can cause high warm idle if it doesn't close properly. It also can cause oscillating idle.

Problem is solved, thanks all for the help.

1 hose to the AAR was a bit loose probably due to the valve adjustment on the right bank + the top hose on the decel valve was pulling false air.

For now, I blocked this hose which is giving a whole lot better throttle response. Will start a new thread on possible side effects...