WUR or aux air valve?

[makaio]

I'm having aproblem with my car not idiling when first started and cold. It stumbles and will not stay running unless I keep my foot on the gas. The kicker is, if I do this for 5 minutes or so, then turn the car off and let it sit for another 4-5 minutes, when I start it back up, it idles like a champ.

I believe it is either the warm-up regulator or the aux air valve. I know what to look for on the aux air valve, check when cold. But how do i remove it, with out messing anything else up?

If it is not the aux air valve, and is indeed the WUR, is it just take the old out and put a new one in? Or will I need to adjust the mixture settings after install?

I have read the Pelican article on making my WUR adjustable, but I don't think my skill level is quite high enough.

The car is a 78 911 SC.

Thanks,

[wckrause]

Sounds more like the aux air valve. If it were the WUR, pressing on the accelerator wouldn't help. Try adjusting your idle real high, and see if your car starts easier when cold. (Just a temporary test).

There are two hoses on the AAV and an electrical connection. It's not too bad to get to.

[hdoody]

Make sure you have 12 volts at the warmup regulator. Also check the regulator itself on ohms setting. I don't remember the exact reading you need, but make sure it doesn't read an open. I believe your model year has a thermo-timeswitch that feeds the wur.
Good luck

[RoninLB]

Can't say for sure what your problem is. My AAV will be removed permanently. IMO, it can cause unnecessary problems and I don't need a problem waiting to happen.

[RoninLB]

Woops....should have written "deceleration valve" not AAV

[Superman]

You can usually check AAVs pretty easy. Wait till it's cold. Take the two big hoses off it. With a mirror and a flashlight verify that you can see through it. The hoses you remove are ones that face each other on opposite sides of the device. Then, apply voltage to it and watch the air passage close.

WUR's are a little trickier. I think you're on the right track though. Stopping the engine after a few minutes and waiting has the effect of heading your engine bay. The AAV and the WUR each have heaters in them that are supposed to work electrically. If not, they still work eventually from engine heat. There is a resistance spec for the WUR, though I don't know what yours is. If you put an ohmmeter across the contacts you might find there is infinite resistance, in which case the heating element is not working.

Yes, if you change your WUR, you will also need to re-set your mixture.

[SeaDweller]

Not to be picky, but I believe everyone is referring to the Auxiliary Air Regulator, not the Auxiliary Air Valve. Also, the thermo time switch controls the cold start injector, not the WUR.

Your symptoms could be caused by many things. The WUR, Thermo Time Switch, Cold Start Injector, AAR, Thermo Valve, improper routing of vacuum lines, system/control pressure, etc. I've found that narrowing down your options by eliminating what's working is the best approach.

If the engine fires immediately, then you can pretty much eliminate the thermo time switch and cold start valve. If the engine runs well when warm, it usually points to the WUR or the AAR. Superman's suggestion to check the operation of the AAR is a good one, however you don't have to remove both hoses. The outer hose is easy to access and remove. As suggested, use a mirror, but shine the light into the mirror itself (reflecting the light) and it'll illuminate the interior of the AAR. An initial check would be to see if the AAR is open. You may find that it's only open enough that the opening looks like a quarter moon, but that's ok.

Another thing to check is the vacuum hose routing to make sure it's correct. I've found that a "quick fix" by some sly mechanics is to re-route vacuum lines and crank up the mixuture so the WUR is taken out of the system for the most part. This is easier than properly troubleshooting the engine.

Finally, check the system and control pressures to make sure they're within spec. The WUR could be slighly out of adjustment and providing too much, or not enough enrichment during the cold start process. If that's the case, then the mixture itself is probably out of adjustment as well.

Does the engine pulse when it's warmed up?

In some cases, there are multiple issues, but I think that's pretty rare. What makes things difficult with CIS is many components can mimick the same symptom, so going through and troubleshooting the entire system is usually necessary.

[wckrause]

The fact that the car idles OK when he presses on the accelerator leads me to believe that the mixture is OK, and he just needs a little more throttle to get a smooth idle when cold. That is exactly what the AAR (or AAV) is supposed to do.

If the problem is with a too lean mixture, then giving it some throttle would cause it to stumble, and possibly backfire.

[SeaDweller]

My engine had the same symptoms, and it turned out that it was not only improperly routed vacuum lines, but too rich a mixture condition. My engine ran very poorly when cold, but once warm, it ran perfectly, despite the overly rich condition.

The difficult part of CIS is that everything operates in concert, so the entire system really needs troubleshooting. A change in one thing invariably causes a change in another area. The only exception might be the AAR, as it serves only to route additional air into the system, but of course, that lack of air might cause someone to adjust the mixuture to compensate.

It's neat stuff when it works!

[makaio]

Thanks for all the input.

When I get off work tommorow, I will check the AAR, and the power at the WUR. If I can't trace the culprit myself, I will have to take it to a mechanic.

I'm taking my wifes VW Passat to the dealership for maintenance on Friday, so I wiill talk to the mechanics and see if they can get my car in for a diagnostics if needed.

I hate to think about taking my car to a mechanic, because I have been able to do all the maintenance on on it myself so far. But i don't have the fuel pressure tester or a CO meter.

[pbs911]

I had been having problems with idle at cold, warm up and hunting. A few weeks ago when I replaced my alternator, I started disconnecting all the electrical connections and cleaning them. Guess what, my idle returned to nornal, no more hunting and great cold start. I know it had nothing to do with the alternator becasue it was charging fine, the bearing was just screaching.

[hdoody]

Duh!
I stand corrected!
Seadweller is absolutely right. My analysis would cause the mixture to be too rich after startup. I thought the start injector operated only when cranking. Got to look at those wiring diagrams again.

[makaio]

Took the hose off to the AAV today. It was wide open.

Checked all the vacumn lines. They are in their place and clear.

So I made a apointment with the wrench to do a pressure check next week.

I'll keep you posted.

[wckrause]

Does your AAV close when warm? It's possible that it's stuck open, and your idle speed is set low to compensate. Just a thought.

[stormcrow]

Matt,

Sounds like your pressure regulator could be the problem. As you describe, when you first start the car, it stumbles and if you keep it running for about five minutes and shut it off and let it set, it starts right up.

The fuel pressure regulator is bolted to the engine so that the heat from the engine helps warm it up. In addition, there is a bi-metal strip which controls the fuel pressure at the fuel distributor. It may be that it is out of adjustment.

When cold, the fuel pressure regulator keeps the pressure low on the fuel distrbutor so that more fuel can go through the fuel distributor and out to the injectors.

As the bi-metal strip warms up, the pressure is increased on the fuel distributor which allows less fuel through the fuel distributor and then out to the injectors.

Checking the fuel pressures is the best way to determine if this is the problem.

If it checks out ok, then I would look at the cold start valve which could also be the culprut.

Steve