1981 380sl-What do you think?

[mattlis]

I been chasing high idle in my 380sl for the past 7 months. So far I tested and replaced:

2 used icm, one was a few years old re-manufactured unit
new ICV
adjusted the TPS
tested all the temp switches
new oxygen sensor
new OVP

I started with vacuum leaks, i replaced everything down to the manifold gaskets and intake plenums, nothing. In May the ICM computer fried out and I replaced it with a used one. With the change in the computer I began to look at the idle system as my problem.

The new computer was sending around 4.5 volts to the valve, in spec, but idling at 900-1000rpm. I flexed and pinched the board and the car stayed at 650rpm all day, and the new voltage was about 5.3 volts. I shorted out the board so the car would idle at 500, and it was sending 9v. I got a new valve cause I read that old valves can't use the lower voltages, put on the new one, nothing changed.

Ok, so I got another computer, a newish rebuilt one. Obviously nothing changed, but why is everything exactly the same as with the old computer? I find it hard to believe two computers are bad in the same way, but I can't think of any other inputs that are causing it to idle high.

I know it has the ability to idle right, with a higher voltage of around 5.6, but what do you think? Do you think it's the computer? If I get another one, it will be new, and I really don't want to spend 300 to find out it's not. Any other inputs I'm missing? all I can think of is the Lambda box.

[abiby]

Seems like you've done the diagnostics on the system and it all points to the idle control unit

Why would two units fail the same way... who knows, but they probably have the same weaknesses from the factory.

I'd buy a couple of more units of Ebay before breaking down & buying a new one. OR...Since you already have two units, why don't you try resoldering the traces in one of them? As twisting works, it pretty well has to be a broken/cracked trace. Nothing to lose and everything to gain.

[RadioTek]

You might want to take a close look at the connectors and card edges. There may be a connector or wire that is flaky. Clean with a soft damp cloth, you want to make sure that you get everything dry before applying power. Look for broken wires and damaged insulation, insulation gets hard and brittle with age and heat.

The most common failure points of electrical systems are 1) connectors, 2) connections, 3) wire damage, 4) device failure.

Scott

[abiby]

He's got a good point.
While you're twisting the card to get the proper operation, you could well be affecting the connections at the same time, explaining identical failures.