PeachParts Mercedes-Benz Forum - View Single Post - 92 300E idle surge

DAVID LEE · #6 07-01-2009, 11:06 PM

Chuck:

My car does have the idle air valve. Why am I messing with EHA? My thought was to eliminate influences and plain old "learning". I've had this car for 7 years and this is the 1st time I have done anything to the engine except replace plugs and the water temp sensor (which also caused a high idle, but consistently no matter whether the car was in park or in gear).

So...I've never had to troubleshoot anything engine related. I've had quite a bit of experience working through all kinds of issues on my old 77 350SL - a completely mechanical system. This is my 1st troubleshooting experience on the closed loop version of the same system. People learn in different ways and my way seems to be to do some reading and then go see what happens when you do "????". Anyway, the inputs that would seem to vary idle speed via the idle air valve are a/c on, gear selector, idle position microswitch, and the air flow sensor position as indicated by the potentiometer. There may be other influences, but these are the inputs I've discovered so far.

By completely disconnecting the EHA connector I managed to remove one whole set of inputs and subsequent outputs. Now to work my way through what's left of the inputs and outputs. What I've written concerning the O2 sensor and the EHA unit are for the most part curious observations and after thinking about what I've observed relative to how they influece the idle speed seem to be inconsequential to the problem I'm trying to solve.

Thanks for the response and I'll check out the sources you mentioned and come Friday get back under the hood. I'll get there - just a little slower than most.