Idle Control Valve not getting power
 

I've been trying to determine cause for the very hard to start situation of my1992 300 E.

I just tested the ICV and when I supply 12 volts to it I hear it working.

Problem is that when I crank starter I do not getting any voltage going to ICV connector.

I have tested all sensor in the head and they are within ohm specs for a cold engine.

When I test connector wires for ICV connector with ohm meter I get 157K ohms.

So what next? Do I have a broken wire somewhere?

Power to the ICV comes from the OVP relay. Check the fuse on top of the OVP relay.

http://i179.photobucket.com/albums/w.../OVPRelayA.jpg

http://i179.photobucket.com/albums/w...d/OVPRelay.jpg

I had previously swapped both OVP and MAS from another 1992 300 with no change.

I like that photo you posted maybe I can figure out how to test wires going from OVP to ICV

I have the same problem. I have a new idle control module on the way. The power comes from the OVP, but has to run through the controller first.

Can you feel the relay operate when you turn the ignition on? Also, is the OVP relay seated properly in the socket?

I did a bench test on my OVP relay, with ground on pin 31 and 12v on pin 15 the relay should operate. Then, I put 12v on pin 30 and battery appears on the 87 pins with the relay operated. This test checks the operation of the relay as well as the internal contacts.

i believe in that car the ecu controls the idle.a more prob cause of hard starting would be not enough fuel.limp mode in that car produces just such symptoms[no power from the ovp relay to the ecu] and thus the hydraulic govenor[eha]on the side of the fuel distributor.you should see at least 40ma at the eha when cranking.

Sorry to just jump in the discussion, but I'm experiencing my own issues with idling problems on my benz, and it uses pretty much the same design (ICU, ICV, OVP relay)...

My OVP, when I pull it out and shake it around a bit, I hear a slight rattling noise. That's probably a bad thing isn't it?

The confusing bit is that it seems to work. I pull it out of the car and there's a notable difference between starting and running with and w/o the relay. It has to be working right?

Just a sanity check, but a relay can't be "half dead" in some aspect. Right?

Thanks,

-Troy

What does the idle control module look like and where is it located?


What relay are you refering to when the ignition is turned on?

I did the bench test exactly as you outlined and OVP tested just as you outlined.

Used tester to see if any ma going to eha from connector. Tester should nothing coming thru.

Also still no volts going to Idle control valve when starter cranked, tested ICV with other power source and I could hear it operate.

It seem something is interfering with the eha and the ICV from recieving power.

Ron, mostly incorrect info so far!!!

The idle control valve on that model & year, is controlled 100% by the fuel computer.

To measure the circuit you need a meter capable of measuring duty cycle.

IF you disconnect the idle valve the computer stops sending that signal to the valve.

You never posted what is WRONG with the car that you want to test the circuit?

IF you have a meter with duty cycle capabilities, ??

The problem I am dealing with is a very very hard to start car when it is cold.

I do not have a meter with duty cycle capabilities, so does that mean I will be unable to diagnosis?

Which black box is the fuel computer? The one with three rows of connectors, the one with two rows of connectors or the MAS relay. I have a spare parts car, same year so I can swap them to see it that helps.

Cold start has little OR nothing to do with the idle valve..

Cold start is related to coolant temp effect on the current flow to the EHA.

Measuring current flow to the EHA with a DMM set to Ma, and measuring that signal with key on & engine OFF is the starting point. MUST have 20Ma in that position.

Thanks, I will see if I can do that tomorrow.

I have a very old Fluke 73, it does not have ma scale, but it can measure up to 10 amps.

Test showed .02 amps when I tested per above. I think that is the same as 20 ma.

Where might I go from here?

Since I have an extra fuel computer I swapped that and the fuel distributor out too, no change.

Since you have 20 Ma to the EHA with key on, you need to operate the starter & watch the readings. IT should raise to 120-200Ma on a cold engine.

If the system fuel pressure is at 75-80psi, the engine should start.

Before I tried anything else I decided to try the other fuel control computer again, the one with three rows of pins since my guess was that something electrical was messing things up.

Well I took connector off of the other one and put in my spare again and surprise the engine started easily and idled smoothly. To make sure that was no fluke I swapped back to the other one and engine would not start so I went back to spare one and again the engine started.

Maybe the connector had corrosion on it and mounting and unmounting the plug connector rubbed off the corrosion. Or maybe somethings wrong with the fuel computer.

I don't know whether I actualy did anything that makes it start properly.

With the way things have gone lately about all I can say is I'd rather be lucky than good.

Thanks for help. Hopefully problem will not come back. If it does at least I know what to do next.