1985 500SEC Idle Control Valve diagnose - PeachParts Mercedes-Benz Forum

Kbball · #1 03-12-2006, 07:08 PM

In trouble shooting my intermitant high idle problem. The ICV seems to be working only part time and I want some confirmation before spending the ouch $500+ for a part. (It is a Euro version part no. 000 141 14 25.)

As the engine warms up it jumps to a higher 1500 RPM at idle. Discontecting the ICV does not change the RPM. Voltage with ICV disconnected while running is 13+ volts. Voltage with engine off is 11.7. Engine off and ignition on I can hear the ICV click when I unplug and plug it in again. Using a VOM on frequency setting, and connected to pins is irratic.

I decided to hot wire the ICV to battery and engine would stall, plugged the ICV again and the idle dropped to normal and I can feel the ICV pulsing or modulating, which it didn't before. Now I unplug and the idle jumps up again as I would suspect and normal when plugged in. The VOM freqency now runs about 59%.

Seems like a sticking ICV to me. I cleaned this valve before, but was a little ginger is doing so and might try again concerned about getting too soaked.

Appreciate any comments.

Kurt

lkchris · #2 03-12-2006, 07:54 PM

Purpose of idle control valve is to provide extra air at cold start--sort of like fast idle cam that works with choke on a carburetor.

Fact disconnecting it makes no difference might be a clue to look elsewhere.

Monomer · #3 03-12-2006, 07:54 PM

after you cleaned it, did you lube it with ATF?

dr_mod · #4 03-12-2006, 08:20 PM

I don't mean to steal your thread. Are you able to measure the pulse that the valve is getting? I might make my own idle controler and would like some measurements of what a working system is like. IE. Frequency, pulse width and voltage. I'm only asking because it seems to me you've fixed your problem. BTW, For those who think otherwise, the cold starting valve is a different valve than the Idle speed valve.

sbourg · #5 03-13-2006, 09:28 AM

If you disconnect the ICV connector and the idle does not change, there are only two likely possibilities. Either the ICV is stuck fully open (remote), or you have an air leak bypassing the throttle. This latter is far and away the most common as rubber air delivery components harden and crack or form loose interconnects with age and heat.

Steve

Kbball · #6 03-13-2006, 10:19 AM

The ICV seemed to work as expected only after cycling with a 12V supply from battery. Idle dropped to normal. When the engine was shut off and restarted it stayed at the normal idle and the ICV was modulating. No other changes were made to account for idle drop from 1500 to about 600. Seems once warmed up an "shocked" it worked fine.

I repeated this step the next day as the same thing happened warmed up to a high idle and only dropped after 12V from battery.

Kurt

sbourg · #7 03-13-2006, 01:07 PM

In that case, I would remove the ICV and clean it - use high-concentration rubbing alcohol or cleaners approved for air intake systems, work the valve from full stop-to-stop.

Steve