1994 w124, m104 Erratic Idle

[donald.tyler]

I've experienced no idle issues till today. Car has a newer upper wire harness, fresh plugs/wires. New vacuum lines. I'm thinking it's a failing ETA but I'm hoping it's something simpler.

Symptoms:
Start up: Jumps immediately to 1600 rpm, drops to 500, engine shutters. Is does this 3-4 times then moves on to the "cold engine idle" symptoms.

Cold Engine Idle: Fluctuates from 1000 to 500 rpm, @ 500 shutters. Repeats this pattern till engine warms up (88c).

Warm Engine Idle (88c): Fluctuates between 600 to 750 rpm. If I place the car in D,3,2 or R the idle is normal (600).

If I start the car when the engine is warm the idle surges to 1600 drops to 500, shutters then fluctuates between 600 to 750 rpm.

While driving the car everything seems nominal. No hesitation in the acceleration sits solidly at 2500 rpm @ 60 mph.

I checked the cruse control and all functions work.

[Hirnbeiss]

Do you have the homemade code reader?

[donald.tyler]

Originally Posted by Hirnbeiss

Do you have the homemade code reader?

I don't have a code reader. No warning lights are illuminated on the dash if that makes a difference.

[oldsinner111]

check the wires going to the eletric throttle body

[Sugar Bear]

The surging idle on my 124 93 300e 3.2L was the MAF sensor. It was many years ago but the symptoms sound similar IIRC. Try tapping the MAF by hand and see if it changes the idle at all. Also check the OVP relay, it has caused problems repeatedly on mine.

[donald.tyler]

One thing I didn't mention is I noticed a secondary wiring loom (P/N: 124 540 42 30) had the infamous deteriorating insulation.

It's the positive battery cable, a ground and 2 sensor plugs. Could this also be the culprit?

[donald.tyler]

Originally Posted by donald.tyler

One thing I didn't mention is I noticed a secondary wiring loom (P/N: 124 540 42 30) had the infamous deteriorating insulation.

It's the positive battery cable, a ground and 2 sensor plugs. Could this also be the culprit?

Since I already had the wiring loom ordered (P/N above) I installed it today. The old one had deteriorated badly and since I was at it I pulled the ETA. I removed the plate to inspect the wiring and it was spotless so that's not the issue. The wiring loom didn't help either but it did need replacing so no harm there.

I fiddled with (jiggled, twisted, tapped, etc):
1. MAF - no affect
2. ETA connection to engine wire-harness - no affect
3. OVP - checked the fuse which was good, don't know what else to do with this besides replace.

All that said I will stop the meandering posts till I can provide codes. However this fixing cars thing is really fun for the mechanically challenged, which I am.

[suginami]

Could be:

bad engine wiring harness

bad ETA

MAF

Vacum leak

[Andras]

The harness to the Throttle Body ETA might be bad. Try cutting into the jacket and look to see if the 11 wires inside have good insulation. Mine turned into powder before I rewired it.

[donald.tyler]

I had the codes read today at Omega here in Portland and the MAF was returning several faults so a new Bosch part was ordered. I installed and the car immediately idled correctly. I couldn't be happier. Thank you to all those who provided input.

[suginami]

Originally Posted by donald.tyler

I had the codes read today at Omega here in Portland and the MAF was returning several faults so a new Bosch part was ordered. I installed and the car immediately idled correctly. I couldn't be happier. Thank you to all those who provided input.

That was #3 on my post above.