My '95 E420 has developed a severe stumble and stalling problem. The upper harness and the idle control (non-ASR car) actuator were both replaced with newer versions. The car has about 59K miles on it, I bought it last year and at the time it had a occasional rough idle but nothing too bad.

The problem developed after I did two things; replaced the breather hose that attaches to the left cylinder head, it's part of the egr/vacuum system, the one that bends at a 90 degree angle and has a hose clip were it attaches to the head. It was seeping and was brittle and cracked.

The other event was I dressed the engine covers using No Touch which I now realize was a mistake since it has silicone. Once I realized that I removed and cleaned the MAF. Reinstalled it and got Codes 4,7, and 9 on pin 4 of the 38 pin connector, code 10 on pin 8 and code 12 on pin 17. I had earlier got code 10 on the 8 pin connector that has the built in LED which lead me to suspect the MAF. Before I cleaned the MAF did disconnect it to see if it made a difference, I did not think it did but cleaned it regardless.

Cleared the codes and no change. I get no flashes at the 8 pin. When the car is stumbling pin 4 on the 8 pin is dimly lit, and the brightness increases with engine speed.

The car starts idles about 900 rpm for a few seconds then bounces between 500-1000 rpm and stalls. I can smell fuel a pungent aroma like rich exhaust.

I have looked at the caps and rotors, no green deposits no arcing. I have new caps and rotors ready to go but I would like to be sure there is not another more obvious issue.

The codes have not returned. I suspect a fuel issue but don't have a gauge to check the regulator. As it idles it will almost stall, catch itself increase the idle and then stumble again and finally stall. I do not know the condition/age of the fuel pump/accumulator/filter. I am tempted to replace the filter to rule it out.

When the dealer replaced the throttle actuator in 2006 they also replaced the the LH module (not sure why).

I have read every E420/M119 engine thread I could find but most have codes or have not replaced the harness(es)

Any thoughts would be much appreciated.

I should add that just before this I added some Lucas UCL and thought the car was running better for a while. I am not getting any CELs

This came from Jim Forgione's web site. Could your O2 sensor be shot? Jim does refer the reader to a link that discusses contamination of the MAF due to use of the silicone product your mentioned and it could cause the engine to go rich, like you described. http://www.k6jrf.com/MB_MAF.html

K6JRF Auto Page
Warning . . .
I was sent a interesting note from another 140 owner who came across the warning from Berryman Products on the use of 'silicone' under your hood. Here's what they say; Silicone of any variety will contaminate the oxygen sensor. And the amount of silicone needed to do this is minuscule. How minuscule you may ask? A well known example is: Silicone-based RTV gasket sealants. These type of sealers outgas small amounts of silicone when they cure. If you use one of these sealers on an oil pan or valve cover gasket, the silicone vapor will be sucked into the crankcase ventilation system and then into the intake manifold. As a result, the oxygen sensor, once contaminated with Silicone will be inoperative within a day or two. Likewise, do not use Silicone-based lubricants anywhere under the hood, or anywhere forward of the firewall.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Thanks. I read his write up and that lead me to clean the MAF. wouldn't the
O2 sensor throw a CEL or a code?

Try tapping on the O2 sensors, then start and see if the car misbehaves. I didn't know about the silicone thing, does it effect all O2 sensors acrose the board? then I would think that it would be common knowledge.

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Tap on the exhaust? Worth a try thanks

hmm i remember helping my friend's car with this, except when it ran it ran fine..
check the spark plugs, and when we changed the caps and rotors, it stopped doing it, although the exhaust still made it smell funky..

Update. Same problem but now getting code 11 from 8 pin connector. I'll read codes from the 38 pin later.

I noticed the air pimp comes on when the car is started but will quickly cycle on/off for brief periods. Then the engine dies. How long should the air pump be engaged?

New codes: pin 4-7, pin 17-12, pin 19-11 which is consistent with the 9in code. All of these are TN or speed codes

I stumble, stall and smell too. It must be an age thing.

The car's fine though!

RayH

Sound like leaky fuel injectors to me.

I would pull them and have tested.

Thanks. I want to track down why the air pump is not running at startup for 110-120 seconds which according to some threads here is what it should be doing. When it is running the car is idling a bit high but fine. When the air pump disengages the trouble starts.

I know I know. Check your fuses.
I was reading all the threads I could find on the TN signal and saw an old Arthur Dalton thread where he reminded someone to check the fuses in the base module which I saw transmits some of the TN signal. Had not done that. Went home and bingo one of them was blown.

I replaced it and the car started idled smoothly and drives fine. I still have occasional bogging but I have new caps, rotors and plugs to install at some point.

Thanks to everyone who helped.