Please help me out of a real pickle - '88 560SEL High Idle

[tinypanzer]

Hi everyone,

I know I haven't been here in a while, but leave it to a 126 to send me back to my old friends for help.

I am in a really bad situation. I've been planning a road trip for months (and paid tons of money for reservations) and now one day before I am to leave for 3 weeks, my idle has shot up to 1500-1800 RPM.

I need a fix FAST!

Here's what I've ruled out:

1) vacuum leaks. All the rubber, inlcuding the intake boot, etc. are new. Vacuuum is good even at 1800rpm.
2) stuck throttle plate
3) OVP relay

Here are some tests I've performed

1) removing idle air wires has no eeffect. Applying a 9V battery to the IAC will cause a near immediate stall. The IAC mooves freely with a 9V battery, and is clean inside.
2) temp sensors sensors seem to measure within spec.
3) voltage to the IAC is 7.6 DC (though I neglected to look for any AC component or duty cycle to the signal) when disconnected from the IAC. When conneceted, it is near zero (measured in parallel).
4) shunting the signal wire from the throttle position sensor had no effect on idle speed.


Can anyone help me shed light on this or suggest some further tests? I am in a real jam here.


Thanks so much,


TP