HELP: CIS engine will not idle

[JP911]

The Porsche Gods are not smiling favorably on my 3.5 twin plug motor. Here's the problem: On cold or warm start the engine will start, try to idle, start to stumble and then stall. This came on rather suddenly at the end of my 4th autocross run this weekend (was running OK before). When moving the car runs fine, but when I stop I have to pull up the hand throttle to keep the engine from stalling.

When I first started the engine about 3 weeks ago I had some problems that were diagnosed by a local shop as a bad WUR (rough cold start with no idle then high idle when warm). I replaced it with a rebuilt unit, had the mixture set by the shop (1.5 CO, 24 deg advance, 950 idle), and all was well. The mixture was deliberately set rich for safety reasons (crappy CA gas).

I've searched the board archives and haven't really found anything conclusive. Any ideas from those far wiser than me?
-Jon

Engine stats (if it's helpful):
SC engine (78-79) base
100 mm P/Cs
3.3 crank
Twin Bosch 6-pin CDI boxes w/Andial harness
Stock coils
964 distributor converted for mech advance
78-79 CIS

[Joe Bob]

Hunting or surging is usually an intake leak.

[Jim Sims]

What's the condition of the air box? Perhaps you should check the seams. Does running rich produce any backfiring?

[Joe Bob]

The LIGHT spraying of carb cleaner or ether/quick start in the suspect areas will pinpoint a leak....obviously you will need someone to keep the revs up so that it won't die on ya.

[JP911]

The airbox is new, but I won't rule out a leak. Thanks for the ideas. Any others care to chime in on my issue?

[pjv911]

Make sure the pop valve is properly seated. Including the epoxy used to hold it in place. However a vacuum leak causing your symtoms would have clearly shown evident on the exhaust analzer so maybe you could have it rechecked once you check for obvious air leaks. Make sure the throttle body/sensor plate boot is secure as well.

Kurt Williams