77 turbo, poor idle...runs fine everywhere else

[zentoad]

My 77 turbo recently started having a poor idle/stalling problem.
It starts and seems to idle fine when cold for a minute or two, then the idle speed decreases, starts to stumble and pop...then will stall.

If I overcome the poor idle with the hand throttle and drive the car, it seems to accelerate and perform with no problems.

I'm thinking its a problem with the WUR?... I am new to Porsche's and I read that the WUR has an effect at all times, not just cold start...

Is this so?

[john walker's workshop]

have a shop with a gas analyzer set your CO to 3.5-4% first. you may just be way too lean. turbos always need the intake nuts snugged up too. be sure the plug is back in the mixture adjusting hole after adjusting the CO, or you won't get a proper reading, and you will have a intake leak.

[81 930]

JW has some great suggestions, as usual. You might be experiencing a vacuum leak somewhere. A common place for this to happen on the Turbos is at the intake manifold to injector block interface. The injector blocks are made of phenolic plastic, which can crack over time causing leaks. Your problem could also be related to your mixture setting. On a cold start, the WUR richens the mixture considerably which may be enough to start your engine and let it run for a couple of minutes until the bi-metallic element inside the WUR warms and begins leaning the mixture. Definitely check your CO at idle. It could simply be too low.

You are correct that the WUR is in effect at all times. On the Turbo engines, it has an enrichment circuit that gives more fuel based upon manifold pressure (boost). For these reasons it might be more appropriate to think of the unit as a control pressure regulator rather than just a warm up regulator.

Good luck. Let us know what you find.

[zentoad]

Thanks for the input guys....

but when I went out to start testing it, the no longer starts!

I had previously started tocheck for vacuum leaks/un-metered air...
but was interrupted, the car sat for 1-1 1/2 hours afterwards

Now no start!

more testing in my future...

Tony

[kepperly]

Next time you get it running, take a propane bottle and put a two foot lenth of small dia rubber hose on it , turn on the propane and run the hose around any suspected leak areas. If you find one that when you put the end of the hose near it and the egine speed increases you have found your leak.

keith epperly
87 slant nose turbo look carrera cabriolet

[bkreigsr]

(to the uninitiated, that sounds downright scary)

no start sounds like one of the fuel pumps?

Bill K

(following thread out of curiosity, also with 77 930)

[zentoad]

Got the car started, after sitting awhile longer...

at the moment I am still suspecteing the warm up regulator, or more accurately, whatever is sending a vacuum signal to it.

it seems that if I disconnect the vacuum line the idle is much improved.
I tested the vacuum diaphragm in the WUR and it holds vacuum fine...
if I supply vacuum to the fiiting of the WUR when the car is idling (existing vacuum line disconnected and plugged) the idle falters dramatically and even stalls...

I am going to find out what parts sends the vacuum signal to the WUR, it seems that it is allowing vacuum to the part when it is not supposed to...

BTW, I did a preliminary vaccuum leak check earlier and found nothing.

I will keep you posted

Tony

[zentoad]

OK, now I see there are two vacuum lines!

the plot thickens....

anyone know where I can get info on the vacuum portion of the system?
Tony

[bkreigsr]

nice work Tony.
This thread is going in my troubleshooting binder.

[zentoad]

not so quick, with the congrats....

while I still suspect the WUR.... I incorrectly assumed that there was some sort of a unit controlling the vacuum signal, and supplying it at the wrong time....

further research indicates that this is not the case.

I am waiting on a manual (always helpful) and getting my hands on a fuel pressure gauge (seems an absolute must when working on CIS) before I go any further....

I think I understand how the WUR functions, with regard to warm up and fuel pressure regulation...
I am assuming (could be trouble) for the time being, that the vacuum lines will measure the pressure differential under boost conditions, and adjust the fuel pressure/delivery accordingly...

If I had read Brian's above post more carefully, I would have made that connection already...DOH!

I am going to do MORE research into the CIS, and proceed with manual and fuel pressure gauge in hand.

thanks for the support/encouragement...more importantly the help and info...


Tony

[zentoad]

Update....

Found some great info on "Jim William's CIS Primer" page...

http://members.rennlist.com/jimwms/CIS/CIShome.html

as reccomended in another CIS post I was reading.

Turns out there IS a Thermal Valve on the 77 Turbo model....


I'll check it out, and update when I get a chance...

Tony