High idle in P and N

Hello

As I recently started trying to get my Grandfather's old Mercedes w108 4.5 on the road again, which my dad have been trying to get running for about 10 years now, I've run into a lot of stuff. The car has been taken to a lot of mechanics who should have experience with the old Mercedes, but no one got it running.

Short recap of what I've done so far.
Got the car home, ran really odd and it has been turned all the way in distributor to even get it to run. First I took out all injectors and found one injector was very wrong for that particually model. So I put in a correct one and threw all the injectors in an ultrasonic cleaner. Made  the car run a lot smoother, but still idling really high in P and N, D and R is fine. I noticed the idle screw was screwed all the way in, so I started looking for vacuum leaks. The hose going to the fender with the vacuum box was leaking, so I've plugged it for now. Haven't been able to test the hose to the brake booster yet. Took off the map sensor, checked the vacuum on it and testet the resistance on the pins. I took off the AAV, which was completly stuck, took it apart, put it  in the cleaner, lubed it and assembled it. Still has that high idle, so I took it apart again and did the same, the piston is moving fine in there and with a torch I can make the thermo thing move. But still when the car is fully warm, I can squish the hose to the AAV and it falls dramatically in RPM, I would say maybe  500 RPM. So I'm still suspecting the AAV, maybe the thermo thing is not moving enough? If I can pinch the hose and RPM drops when fully warm, it must be that? It can't be a vacuum leak? 

Was looking at AAV's on the internet and holy, they are expensive,  even just for a refurbished one, even then if you go and get  a refurbished, I would be unsure whatever or not it would be better than my current? 

Any tips would be appreciated, my own next step would be to buy a new AAV.

(Also just bought all special tools to check time the valves and do a compression test, so doing that soon as well. Even though I think compression is fine. It drives fine in D and R and takes gas.)-Jakob   

Welcome to the forum, Jakob!
I like the car you own very much!
Congratulations for getting the car running again.
I think your idea is correct - the AAV isn't in correct function. The wax-element gets old and will never again work as it should do - it has to be replaced.
Looking at your car, I think you're localized in the U.S.A?
I don't know who can repair it there or where you can buy a replacement.
But don't destroy it by following some specialists on the WWW.
Rapair isn't so easy and special parts and knowledge is needed to do the job.

Regards
Norbert

I am located in Denmark, it was imported to Denmark when my Grandfather bought it. As said, I've already had the AAV disasembled completly twice, so I'm not afraid of disamembling it again if only I can find a replacement wax-element. I'm a mechanic myself, so I have press etc which worked great.

I can find some German websites where you can send your AAV to get refurbished, but that still costs a lot.

Hi,

it is true that AAVs fade over time. Both from thermoelement and from sealing. Asyou have already diassembled it, I hope you did that well and did not destroy anything inside. If have seen many broken AAVs in our workshops. Normallly I always have an overhauled one for MB 8-cylinder Mercedes-Benz with me to show the difference.

Hi,

and be aware of this kind of rework of AAVs. jetronic.org/de/kunena/jetronic/2390-zls...me-ueberholung#22563

Used a shop press, it glide out without the meter ever reaching any preassure. No damage to the AAV at all. Unfortunatly it didn't solve my problem, it did help though. The car is without a tachometer, but from the sound alone, I'd say it went from 1800 to 1300 RPM in idle. The AAV was completly seized before my disasemble. But it should still be my problem when pinching the hose makes it drop to normal RPM in idle?