Confused Aux air valve.

[PanzerSD]

When I start up my 4.5 cold (aprx. -5 or -10 C) it idles fast at about 1000RPM and at times 1500RPM which I feel is almost normal. then the engine warms up and the idle might drop to 900 or 950. In gear, the idle is nicely around 550 or 600RPM and idles smoothly..very smoothly in fact.
However, after I've been driving for a while and the engine is HOT like 80C or hotter, the engine still idles fast.
Some have said AAV is stuck open, other say I have Vacuum leaks; But my AAV or something may be getting confused so to speak. There is the odd HOT start that begins low at around 600RPM and very slowly works its way up to 900RPM, but VERY slowly.
Then I can shut it off and the next start will shoot right up to 1500RPM. I've also had a couple cold starts that started at 550 and stayed there till I revved it up then it hung out at 1000RPM. My 'in-gear' idle is always 600RPM (-/+ 50RPM).

I see the AAV has a heater element in it to simulate hot water (why?) could that be malfunctioning somehow? Is there some resource that has a lot to do with the AAV? the ETM is somewhat vague on that particular item, and is merely mentioned in the Bosch CIS manual.

EDIT: I should also mention that my idle screw is cranked all the way in and turning out only increases the idle. The mixture screw on the fuel distributor is seized solid and appears to have been stripped in the clockwise direction. It IS a slot head thing correct? or is that merely the safety plug they speak of?

[winecountryone]

Mixture screw should be an allen/hex key,4mm IIRC.The slotted screw is just a cover plug.Is your ignition timing spot on?Advanced timing,or a "sticking" distributor advance unit might be the cause.

[PanzerSD]

now we're getting somewhere! Ok, so if I can't get that plug out...then what? Well, I guess if I can't get the plug out then it probably isn't going to need adjustment. How much does that little adjustment change idle speed?

The distributor can cause a fast idle?? The engine idles pretty well when it decides to idle at an appropriate RPM, I was surprised, I was expecting a lot more wrong with it than it has. I'll mark the distributor and play with it.and see what changes it makes.

[PanzerSD]

Funny, I can remember posting this in the Tech forum....Hmm

[250 Coupe]

The mixture screw in the fuel distributor won't effect idle speed all the much but will change the CO2 quite a bit with a small adjustment. I would not tinker with it until you get a good idle and then only with a CO2 meter or let a shop do it for you. I have a meter and keep mine set at 1-1.5% at 650RPM.

Since you have the idle speed screw cranked in all the way, you have vacuum leaks somewhere.

There are two hoses that form a wye under the throttle valve. There are eight rubber sleeves that connect the upper and lower intake sections. There are the hoses at the aux air valve and finally, there is a bunch of hoses at the rear of the intake that include the modulator valve connection that you asked about earlier and the brake booster, among others.

I'm gonna back away a bit from my statement that your aux air valve is stuck and have you check for vacuum leaks first.

Two ways that I use are carb cleaner sprayed on any area I suspect a leak and listening with a rubber hose. It may seem silly at first but if you stick the end of a hose in your ear and poke around the engine with the other end, you can find even very small leaks. Just make sure the hose is clean or you won't understand the odd looks from others when they see the black ring in your ear.

Engine timing will greatly affect idle speed. There is a vacuum solenoid valve that brings the idle speed up when the air conditioning compressor is on and on some cars will bring the idle up if you turn the steering wheel to a hard stop.

You can eliminate the variables of solenoid valves by disconnecting hoses at the distributor. To check the mechanical advance, you will need to poke around inside the distributor.

Michael