I think I might have found the cause of high Idle. M103
 

Some of you know I'm chasing a high idle. When It warms up it will steadily go to 2000rpm in P and N and when I put it in D or R it comes down to a notch under 1000rpm and recently it will settle around 800rpm and when the AC is on it will drop a little more to around 700rpm.

I've changed all the vacuum lines and rubber parts (all of them). The gauge for the vacuum is only completely to the left when I'm crushing on the FW, with normal driving it's a notch towards the right.

Today when the car was started up (cold) and while the car was running I was leaning on the air filter housing and to my delightness the engine stayed at 900/1000rpm, no surge to 2000rpm! Ran it in D and the RPM would stay at 700/800rpm. Turned the engine off and when I restarted it again it would immediately go to around 1800/1900rpm, after pressing the air filter housing firmly again after 20 seconds the idle went down and stayed at 900rpm in P. When the engine is hot it will immediately go to 2000rpm.

When I replaced the rubber boot underneath the MAF I had a hard time getting it fitted on the throttle body and I suspect now that's where the cause is. Or could it be the gasket for the throttle body or anything else?

Anyways, what's the best way to make sure the boot go's firmly on the throttle body, it's sort of guess work when installing it?

Try a rubber lubricant.

Spray around with WD 40 to find a leak......

I did all that, made even a home made smoke machine. I was thinking it could also be the intake manifold. By putting pressure on it I could have pressed a bad gasket. We will see when I do the head gasket in the coming weeks and change all the gaskets and seals.

Is there anything electronic on the inlet manifold or on the throttle body? Is it possible that leaning on the air filter box is flexing some electronic connector juuuuuuuust enough to make connection properly? Lord knows I've chased down more than my fair share of electronic gremlins in my cars. Any time I have flaky behavior, the first thing to come out nowadays is the soldering iron!

I always had the suspicion that it could be an electrical problem...Something to look into in the next couple of weeks.

A quick check of bolts and nuts with a torque wrench might work before tearing into it.

Vac gauge pulsating all over is a classic sign of vac leak.

I always removed the disk in the MAF to access the rubber boot from the inside,
makes it a lot easier.

With feeler gauges it is not very hard to align the plate when reassembling.

I used Locktite 221 for the bold, not sure if it is necessary, but better safe than sorry.

Rob

You might be right but the manual points to the air throttle valve .It sits under the air box and fixed in with a sadle and 2 bolts with a electrical plug on the back end .Take valve out and clean it with carb cleaner check the hoses that are on the inlet and out let on the valve they go under the fuel distributor.

The airflow potentiometer can affect idle. More than likely you were moving it when you leaned on it.

Yes, airflow potentiometer. I changed mine. It was the cause of the car not idling. The position of how mounted affects the idle speed.

I've changed the airflow potentiometer ( I have four of them on the bench) and adjusted it correctly.

Every time when I had it in spec and the idle would be good (not perfect), the idle go's up again to 1800rpm after restarting the car. Now an od thing happens and this happens with all four airflow potentiometers. When adjusting the potentiometer after a couple of minutes of moving it to get it into spec, no matter much I move the potentiometer around the idle would stay the same but the voltmeter would measure a change in voltage.

Push the electrical connectors pins into the plug housing from the backside of the plug and make sure they're seated and snap locked into the plug. They can still work and move a hair and disconnect the circuit.

1/16" pin punch and push on the brass pins wire crimp.