M103/190E Twitching Idle and Error Code 29
 

Hello,

It has gotten quite cold here in socal and my 1993 190E 2.6 is having some odd problems.

I noticed just starting today after work that my car doesnt idle anymore. The tachometer twitches like crazy from 500-1500 rpm, engine feels rough, and I hear an odd clicking noise coming from EZL/ABS area. Engine will also stall on its own randomly in this state.

I replaced the OVP with a spare that I had (first instinct) and the problem still exists.

I checked the blink codes and I am getting error code 29:

I am about to swap the ECU out for a spare that I have. I am going to leave the battery unplugged over night. Can anyone else suggest other places to look?

The coolant temperature sensors (black 4 prong and blue 1 prong) are new from dealer as of august 2010. Interior cluster temperature gauge does not seem abnormal.

Replaced ECU with spare this morning, twitching tachometer and rough idle still exists.

I do not hear a clicking noise coming from ABS/EZL area anymore though.

does anyone have any information on what this part plays in idle?

http://img207.imageshack.us/img207/8818/0075422917.jpg

Description: Speed Control Sensor; Idle/Cruise Control Impulse Sender at Rear of Instrument Cluster

I think this might be the culprit because just recently, I went to adjust my dimmer on my instrument cluster and my electronics flickered for half a second and came back online. engine almost stalled but caught itself.

Here is a video of my twitching tachometer. This is at idle, engine warm.

http://www.youtube.com/watch?v=hraU0Ho1EWQ

Looks like the Jetronic brain is going haywire with the data it is receiving.

Pull the plug off the EHA and disconnect the O2 sensor. This will run the car in open loop without any electronic assistance. Does the problem still occur or does the car fail to run?

Also double check your resistance of the temp sensor on the head is within spec both cold and warm.

I did check the resistance of the 4 prong black coolant temp sensor after engine is warmed up (> 80C). it reads 230ohms across one set of terminals and 215ohms across the other. I dont think this discrepancy is large enough to cause error, but it is within the spec

http://img.photobucket.com/albums/v2...g?t=1291235148

I will try to cause open loop condition by disconnecting O2 sensor on my drive home from work. I cannot access EHA so easily without removing airbox.