E500 missing

Hello List,
I have a 94 E500, 65K miles. This evening I drove the car from work to the airport (about 50 minutes) to pick up my wife and it was running fine (ambient temp in MN – 78 degrees). However, on the way home the car exhibited a noticeable miss. It felt like a surge every 5-10 seconds. I was worried it was going to stop running, but it did not. I could accelerate fine and it didn’t seem to miss when I accelerated hard. However, driving along at a steady speed you could feel it hesitate in the 5-second cycles. When I stopped at a light with the engine at idle I could see the tach drop slightly matching a rough idle at the same time. My car has the stock chip and has never exhibited this problem previously. Any idea on things I should check? Thanks for your help! I do the work on my cars myself and take pride in understanding the mech. And electronics of these fine machines. The problem is knowing were to start looking and hopefully someone else has had this problem and can help me out.

John
94 E500
89 930
98 528i

I had an additional thought on the hesitation I am having on my E500. That is that perhaps the oxygen sensor has gone bad making it run lean then rich thus the hesitation. When I accelerate hard it doesn't happen which I believe would be the case with an oxygen sensor as the computer would take over and run it rich thus taking the sensor out of the equation. This is just a guess on my part and will need to check the O2 sensor to verify if the case. Has anyone else had this same kind of experience with a ad O2 sensor? Obviously open to other ideas too. THANKS~ John

[Michael]

At wide open throttle (button under acc. pedal depressed), the O2 sensor is indeed offline. When my O2 sensor was going bad, but prior to illuminating the "check engine" light, at 1/2 to 3/4 throttle the car would surge a bit, just noticeably.

Frankly, your symptoms sound like bad distributor caps-the M119 in your car eats the distr. caps & rotors every 50-60k. I doubt the O2 sensor would make it feel like a miss.

Good luck!

Michael,
Thank you for the input and suggestion. I went back through the records and found a receipt for a item called distributor (119-158-01-02) $85.60 each ~ I am assuming that is probably the cap and another two items called Distributor (119-158-02-31) $37.60 each ~ which I assume is the rotor. It looks like those were replaced as part of the 60K tune-up. I should probably take a look at them anyway. I assume when they go bad it is somewhat easy to tell; Carbon traces, burned rotor tip and burned contacts in the cap?

I described it as a miss, but it would probably be more accurate to describe what I am feeling as a hesitation or surge. Thinking about it, I doubt I would actually feel a miss unless a number of cylinders were cutting out at the same time.

I found a number of responses under a search for oxygen sensor and ways to check it in the list history so I will give that a look tomorrow. What is the typical life of the O2 sensor in these cars? I am used to them going 100K miles, but have heard Audi's V8's are hard on sensors and they last only 60-70K miles - if this is true from your experience with V8 in the E500 it helps me feel I am pointed in the correct direction.

Appreciate the help,
John

[Michael]

Per factory spec, they are to bereplaced at 60k miles. I didn't do mine until 80ish, and I waited too long.

You are correct as to what you'd expect to see w/ bad caps & rotors-really sounds like yours are new, though.

Change your O2 sensor (early cars have 1; later cars I believe have 2)...then, what I'd do is pop open the CAN box (where the battery is usually), remove the LH module for 10-15 minutes, then re-install. This will re-set your fuel injection, and you will go to full rich; your car will then begin to adapt itself, slowly.

Good luck!

Michael,
Thanks for your inputs previously. I replaced the O2 sensor which was pretty easy to do. Nice that they make it plug into the side of the tunnel rather than like Audi's where they have the wires snake all the way up into the engine compartment which is hard to route. I did need a O2 socket rather than a crows foot to take out the old O2 sensore and put in the new one. THe crows foot the manual calls out didn't have enough clearance, where the socket fit on and removed pretty easiliy.

The good news from all this is that the car runs perfectly now.

Thanks again for the help!
John

[suginami]

Just an idea, but on other Mercedes engines, when there is a surging / fluctuating idle, some common sources are:

1. throttle actuator
2. mass air sensor
3. vacuum leak (which may give you bad codes suggesting that either / both numbers 1. and 2. are bad).

If your car is missing, a common source is a bad spark plug wire or bad boot.