77 911 Turbo- idle/stall problem -High control pressure?
 

Hey guys,

I've been getting lots of good info from this and other forums, especially Jim Williams CIS Primer...here goes:

I'm working on a 77 911 Turbo that developed a poor idle after warm up. The car starts fine when cold (and warm), but after idling for approx 2 minutes the idle deteriorates and eventually will stall.(car will start warm, but idle will fail) Even though the car is a 77 and I've read otherwise, it has a hand throttle. If I use the hand throttle to keep the car running, it seems to perform well throughout the RPM range.

I've tested the fuel pressure, and after getting my hands on a Turbo manual supplement, it looks like my cold control pressure is high. I've read about adjusting the WUR, and figure that is what I will end up doing, but before I go there I wanted to bounce it off some people with more experience than me.

This is what I found:

No unmetered air leaks...until I pinched a hose from one of the decel valves, trying to eliminate it as a problem...wasn't there initially.
Aux Air Valve...17 ohms/ @5/8ths open when cold/ closes slowly when voltage is supplied.
Thermo valve...able to blow air through when cold
WUR diaphragms ok/ heating coil resistance ok
WUR fuel inlet filter mostly clean/definitely not blocked

Fuel Pressures:
system pressure....5.7-5.8 bar
cold control pressure... 1.8 bar @ 16 deg C*** spec@ 0.8-1.2 bar
warm control pressure... 3.0 bar
(manual does not call for applying vacuum, but when I do control pressure rises to 3.8 bar)

I have had trouble finding specs and info that match the car...

I've seen AAR resistance specs at 33 ohms and 17 ohms.
Most places say the car should not have a hand throttle...it does
PET list one decel valve... I have two.

other components:
vacuum controlled WUR
thermo valve seems to control one decel valve, not the WUR as I have seen in other info

Before adjusting the WUR, I have concerns. Will that throw my warm pressure readings out of spec, or will it only effect the action of the bimetallic spring?

The car was running fine, I have too assume the vacuum lines are plumbed correctly.(though I hate to assume, I can't locate a diagram that corresonds to the car)

I've e-mailed Jim Williams, but I understand he may be a busy guy, so I figured I'd post it for all to see...

Any input would be appreciated.

Thanks for you time...

Tony

stalling
 

raise the idle speed 1/2 turn at a time..until idle maintains..you may have to recheck idle co..it may be too lean at idle

Im not trying to change the subject but im very interested in seeing your hand throttle do you have a pic? Ive never seen or heard of a 911 turbo ever having one.

Your "second" decel valve might actually be the Auxilliary Air Valve as they look very similar in some applications.
The WUR is off spec lean according to your listed cold pressure specifications. What is the idle CO% ?
Can you not simply increase the warm idle setting using the idle adjustment screw?

Hey guys, I found the problem,

the hose clamps at the turbo outlet had come loose...
(didn't think to spray the carb cleaner down in that area when checking for vacuum leaks....you live and learn ;)

I took a really long look at the car and found it, I was verifying all my info, I didn't want to start making adjustments yet because I wasn't convinced that I hadn't missed something. I didn't want simply to compensate for some problem I missed!

just think, if I had found the leak right away, I wouldn't own two new manuals or a fuel pressure tester, and I wouldn't have a new undestanding of how the CIS operates

well at least I have now completed my crash course in CIS!
next I plan to tackle the MFI...maybe later!

Tony- I'll try to post a pic of the hand throttle soon...

Brian- I am no expert, all I know I've learned from boards like this one, and Jim Williams CIS page. my understanding is, that while the decel and AAV look alike- the AAV does not have a small diameter vacuum
line attached to the "back" side.

Thanks to Jim Williams and everyone who has shared there experience for the benefit of the rest of us...

Tony

ditto on the hand throttle, my 77 930 has one.
I did not know it was odd, felt right at home there after driving a 73 mfi for 27 yrs!
Bill K

cool post a pic if you can this fascinates me because in all the books i have on 930s they never show one with a hand throttle. Is the the same one that was used in the normally aspirated car. How common are hand throttles in turbos?

hope this isn't considered a hyjack as the thread problem has been solved? just some related 930 trivia.

hand throttle is the same assembly that is in my 73
same location, and same function, (pulls throttle cable in to pre-adjusted stop).
Bill K

The early or mid-year cars had hand throttles in place of AAV. I'd MUCH rather have hand throttle control rather than the AAV or AAR.