911 1976 Idle changes

[wa3vez]

Just had fuel distributor and warm-up regulator rebuilt. Engine running fine. One problem left. With a warm engine the idle changes from 1400 to 700 rpm and stalls out. Sometimes sitting at a light the engine will drop from 1400 to 1200 and then 700 staying at each for a few seconds. I have not had a chance to check the air lines to the auxiliary control valve yet.
Can the valve be rebuilt? In case I have to purchase a new valve how can I be sure that this is the defective component? Is there a Bosch equivalent that is less expensive than an original Porsche part? Thank you!

Howard Lefkowitz

[stlrj]

Do you know how to adjust the mixture? That would be the next step.

[Bob Kontak]

Originally Posted by stlrj

Do you know how to adjust the mixture? That would be the next step.

Only thing I push back on is if there is something like a vacuum leak or a hose disconnected vs adjusting mixture right now.

[boyt911sc]

Originally Posted by stlrj

Do you know how to adjust the mixture? That would be the next step.

You don't adjust the fuel mixture on the fly. Use some common sense for solving simple problems. You might need to adjust the fuel mixture but check for vacuum/air leak first. Fuel mixture setting does not change unless there is a reason like low fuel pressure or unmetered air. Look for the cause of the problem and start from there.

Tony

[stlrj]

Originally Posted by boyt911sc

Fuel mixture setting does not change unless there is a reason like low fuel pressure or unmetered air.

Tony

Or maybe a rebuilt FD and WUR.

[ossiblue]

I agree with Tony. Don't jump to conclusions and do diligent diagnoses. You have a rebuilt FD and WUR but you haven't told us if the idle issue began with the installation of these components or if you have tested the fuel pressure since the install. Have they been tested? Do you have the fuel pressure readings? Of course, air leaks are a potential problem as well and a likely cause. Have you tested for air leaks? Don't even think of replacing the control valve until you test for leaks. If everything checks out--fuel pressures, no unmetered air found--then you can suspect the air valve itself. Adjustment of the mixture screw should be done only when all other components of the fuel delivery and vacuum system have proven to be within specs.

[wa3vez]

The CIS rebuild has been a process which ended up with the rebuilt FD and WUR by a Porsche Shop. It started with some cleaner in the gas tank, injecters, seats etc. etc. Mixture was set using exhaust gas readings. The changing idle is a new problem that was not present before the CIS rebuild, although the car had not been driven for over a year.
I am anticipating another step by the mechanic involving a new auxilliary air valve. I did not find any air leaks or defective hoses. In checking the Internet I found many cases where the valves had corrosion limiting the valve operation. A new Porsche valve seems to be over $700. I found several descriptions of successful rebuilds. In one case someone used PB Blaster and after soaking overnight the valve worked fine. Any thoughts on this?

[wa3vez]

Auxiliary air valve was sticky. PB blaster fixed it.

[ossiblue]

Originally Posted by wa3vez

Auxiliary air valve was sticky. PB blaster fixed it.

Good news and good for you, too. Best of all, you posted the solution to your problem so others will benefit when similar issues arise for them.

Job well done.