Idle control valve broken?? W126
 

My 380SE -85 started to idle below usual 500 rpm. Sometimes went to 1500 or fluctuated between 400-2000 rpm. Finally went to steady 2000 rpm. Suspected idle control valve, switched ignition on and pulled the electrical connector from valve and measured (almost) battery voltage from harness.

Installed harness back to idle valve but no clicking! Disconnected the electrical connection and tried again back and forth but no clicking.. I´ve cleaned the valve few times previously which have cured the idle, but the valve is now not clicking any more. Then I measured 4 Ohms resistance from idle valve (harness disconnected).

Am I right that the idle control valve is broken? It is $670 at dealer here, please let me know if I should test the valve further.

Finn:

I suspect you've gone thru the search facility here, but I'll post this anyway:

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=523200&sortby=lastpost&sortorder=descending

A member named DPETRYK has had much to say about his trials and tribulations. It seems using a different cleaner helped him. One pro tech mentioned supplying an exciter charge in one of these threads.

Good luck.

Try pulling the connector off the valve just enough to get your test leads on the pins and measure the voltage. Start the engine and let it idle. That way you can see what the idle relay is sending to the valve. I don't have the manual in front of me, but I think you should see 4 - 6 V.

Thank you. Yes, I´ve spent hours with search mode. The valve is not reacting to battery voltage! I already pulled the valve and control module. I opened the control module box and found burned spot from the pc-board. Maybe caused by the defective valve.

How I can test the valve on my table with multimeter? Is the 4 ohms telling anything?

I'm not aware of a table-top test for the valve. The test in the manual says basically that if you are getting the right voltage to the valve and the valve doesn't work, then the valve is bad.

Sparay it with WD-40 and let it set overnight. Mine did the same thing and it sat overnight. It worked in the morning. It would not move even with direct battery voltage until it was soaked.

ctaylor738 , Meza, thank you for your help. I soaked the valve hours in carburator cleaner and then soaked it overnight with WD-40. It did not work. Finally I gave 12V straight from the battery, and the valve clicked. Put back to it´s harness, no clicking, so the manual says the valve is bad. I think the valve is worn out, it will draw too much current from the control module, I found that one transistor on pc-board has overheated. Old posts say that good valve should give 10 +/-2 ohms, mine gives 4 ohm, it´s not ok.

I will replace the idle valve. I would be able to save the control module if I could replace that burned transistor. I can´t read what is printed on the top of the transistor(?) because it´s so badly burned. Is there available circuit diagram of pc-board anywhere? Or what would be that transistor?

I was just going to sugest re-soldering the pc board for the valve, but since you mentioned the burn marks, I would say replace it. I had the same problem on my fuel pump relay, after resoldering, it worked for a while but then started failing, this will repeat over and over again, but since the valve is expencive, I'd look for a used one, just go somewhere where they don't know what a benz is, grab some wires as a cover up, throw the valve over the fence and pick it up free on the other side :)

xp