912E idle speed problem

[Rosart]

Originally posted on the 911 technical forum

I'm getting crazy and I need help.

The engine is running perfectly (no loss of power, acceleration OK, consumption OK,..) BUT the idle speed is too high and stable.

Even if i turn clockwise to the maximum the screw to tune the idle to the min, I still have 2.000 RPM.

Fondamentally no change wathever the position of the by pass screw of the air intake sensor (a little bit higer when getting less reach compared to the max).

By pass air flow completely close and idle speed tuning screw completely close : +/- 2.000 rpm

If I completely close the "input" of the air filter box, I loose 100 or 200 rpm but still running too high. (I don't know how enough air can enter in the injection but I have no "leak" (I mean undesired air input somewhere in the injection)

BUT if I disconnect the input of the auxiliary air intake (air can enter directly and not from "after" air filter and air intake sensor); the speed fall down. If i place close this input with my finger, it's running too high and I feel that air is aspired by this input. If I let some air enter, speed is sligtly falling until motor stop wen fully open.
I'm getting crazy so if anybody has an idea...


Thanks

[WFBowen]

Rosart:
I'll keep this thread alive, but I have no real cure. I'm assuming you're absolutely certain that every possible air entry between the intake valves and the airflow meter are sealed. Double check the intake runner boots and the intake to cyl. head gaskets. Make sure that all vacuum devices (distributor advance/retard canisters; decel valve; egr valve) hold vacuum. Did this happen suddenly or gradually degrade to this condition?
Also, make sure your distributor advance is not hanging at low rpm. , Double check the crankcase & oil filler for leaks - they're part of the sealed system. You've probably done this, but the best way to check for leaks is to CAREFULLY spray small amounts of carb cleaner around sealing areas to see if rpm's change. Make sure the throttle butterfly isn't binding and is closing all the way with no air leaks in the cross shaft.
Good luck,
Bill.

[eki912]

Check that auxiliary air valve. Take it out , put it in a freezer..... it should be open when cold. It has two contacts if you put 12 volts in to those , it should close slowly. Eventually it should be closed completely.

I saw on 912bbs , there is guy who is running his 912E without any vacuum hoses fitted , just a "radiator hose " connected between AFM and throttle body.

Maybe worth trying that too ??? Naturally , it wil be harder to start , without that Aux air thing.

Get the 912E L-JET manual , from texas site. It is in links down there. Free to print out. Many L-Jet problems can be checked & fixed by using that manual.

eki