w124 1994 looping idle, sometimes....
 

Problem: A 1994 e320 with a looping idle on occasion. Loops from the 700 to the 1200 range a half dozen times before settling down (note, only in park or in neutral).

The check engine light came on and my mechanic (Enrique on Reseda) said it was the O2 sensor so I had it changed. The light came back on and the idle looping returned once in a while so, based on research on this forum, I changed the coolant temp sensor. No luck.

I took off the MAS and cleaned it with MAS cleaner and it was better for a day but the check engine light came back on and now its looping a bit more often. Maybe I made it worse.


Can it be anything else but the MAS at this point with the intermittent looping idle. I figure if it was a vaccum leak it would be a constant looping idle?

The car has 120k miles and the harness was done at about 80k.

Thanks in advance for the help!

John

Have you checked the fault codes - e.g. pins 3, 8, 14?

Check vac line at fuel pressure regulator for evidence of petro..there should be none in that line. If there is, change the regulator.

Also check all vac lines for leaks, specially the white plastic one under the front cover.

I am going to check the codes and the pressure regulator tonight. Some good leads, I'll report back tomorrow.

Out of curiosity, how can I check pin #3? Isn't that the power supply for the code reader? Are you saying a 3 error code on pin 19 - lambda control perhaps?

Thanks again for the leads folks.


-John

Pin 3 should be the DM/diagnostic module LED, pin 16 the 12v, pin 1 the ground.

Ok, I was looking at the data link connector not the diagnostic connector....I'll run the checks again tonight and get back to you....

I just moved so I could not find my LED tool so i had to build another one.

I'll have to check codes tonight.

In the meantime I replaced the MAS and the car runs like new, unreal. I want to make sure that's the only problem so I'll check codes tonight.

I built the new code reader into an old mouse I had laying around - very ergonomic...