3.2 Idle Problem
 

A shop is in the process of installing an '88 3.2 engine in my '73 911. It's in and complete but my mechanic has been chasing a problem for a few days. Engine is hard to start and at idle, it will cut out for a while and die. Sometimes it will idle well for a couple of minutes and then this problem will start. Anything off idle, it runs fine. He pulled of an injector electrical plug and attached a trouble light and when it was idling okay (a little rough because one injector wasn't functional) the light was pulsing as normal. When the problem kicked in, you could see the light going dim or pulsing out of sync. Also, when you put your hand on the DME relay, you could feel it clicking like crazy when the idle problem started. The DME and the relay have been replaced with known good ones and still have the problem. Flywheel sensors have been replaced and gaps checked, double checked. All injectors were plugged, so they were replaced. $$$ This engine is unknown to me as I bought it from someone long distance. Also, it came without a DME and harness, so there is another variable. Have learned some tough lessons on this whole deal so far, but has anyone experienced anything like this?

Sorry to hear you are having troubles, but here are my observations:
1. the clicking relay means either the power from the ignition switch to the relay is pulsing
or
2. the ouput from the dme to the relay that controls the fuel pump side of the main/fuel pump relay is pulsing.
Probably # 2.
Have you checked the idle position switch, and idle speed control valve? It sounds to me like the dme is thinking 'engine has stopped, need to shut off fuel pump now', so you get the clicking you refer to. I would verify the wiring to these components, as well as speed sensor, and reference sensor all the way to the dme . My guess is that at idle the dme is gettiing a bad signal. Does disconnect of the oxy sensor change the idle?
Good luck,

This problem turned out to be a bad coil. Weird

Hmmm....I don't see how a bad coil could cause the DME relay to click. The only real connection between the coil and the DME is a pulsed signal to the coil from the DME.

Interesting. I hope your problem is truly solved.

Mike

I agree with IROC. The DME unit is NOT that sensitive to RF from the coil.
Could it be that the shop found the problem, e.g. a bad idle switch or broken
wire, and replaced the coil in the process? Once parts get replaced, they
usually don't get removed. Shops sometimes have a problem justifying
3 hrs labor for a broken wire.

Have Fun
Loren
'88 3.2

Does the relay still click as originally described?

The theory is that a short in the windings of the coil fed back into the DME causing this problem. No, the DME relay doesn't click anymore. I have known the mechanic for a long time and consider him a friend, so I believe he is straight with me. He called his network of top wrenches in town and one of them suggested that it might be the coil. He obviously hadn't seen the problem before and felt as you do, that a coil problem wouldn't cause these symptoms. I drove the car tonight and am really pleased with how it runs and it pulls pretty hard. Unfortunately, my budget is totally shot, so the other upgrades (22/30 t-bars, brake upgrade, shocks, etc) will have to wait.