Hi fellows,

I am facing an annoying 'High fluctuating idle', issue, which developed suddenly yesterday, after having inspected my throttle body for gunk, just by pushing down the Air Flow meter plate and pushing the throttle linkage to WOT. No cleaning - nothing touched.

After that, I pulled a small vacuum hose on the back of the Intake Manifold and plugged in my vacuum gauge. That was when i observed the hight idle.I plugged back the vacuum hose, but the high idle remained.

This morning I started the car from cold, and the problem came back as soon as the engine came out of Cold Start mode. It is like oscillating between 1000 and 2000 RPM once per second.

I have checked the IACV, applying battery voltage, and it clicks fine.
Also the IACV connector shows 12V, however between pin 2 and Ground (The manual says pin 1 and ground); not quite sure what that means?

Finally, I noticed that during the high idle, there is a noticeable suction and hiss from the Throttle Body opening, and by covering it with my hands, as tight as possible, the RPM drops.

So my conclusion is that the butterfly valve is not sealing as it should during idle.

Could this simply be a question of cleaning the TB? Why would it have developed so suddenly? Or is it more likely that the linkage is sticking or pushed out of adjustment. The problem started only after I had pushed the linkage back and forth a few times?

I will try to lube the TB linkage tonight - but does anyone have suggestions for further investigations?

BR
Viggo

What Car? What engine?

Oh, I am sorry.

W124 300 E, 1990
Engine: M103

/Viggo

Over voltage protector.

__________________
600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

I pulled out the OVP and tested it; no issues.
Then I removed the IACV and tested it; obvious issue - it didn't move when I applied a pulse. Clearly dead.

Luckily, my local shop with Mercedes expertise and a lot of old used Mercedes parts lying around, had a cheap replacement.

I will install it tonight, expecting it to cure the problem.

In fact, part of the prehistory is, that the engine suffered from low fluctuating RPMs and stalling a few weeks ago, prior to the present high idling.
So everything points to a IACV that was' kicking the bucket'.

/Viggo