My wife's 94 E320 wagon (120 k miles) suddenly developed a rough idle yesterday morning, in town, 5 miles after it was started. She drove it 25 more miles, mostly highway, no change and no check engine light. That afternoon I drove it back home. It started fine but idled rough, and the check engine light came on immediately. It seemed to shift very hard the first few miles but maybe got better after warming up. I drove it home (30 miles). On the highway it ran OK, but maybe a bit rough intermittently, and seemed to lack power.

I've searched archives--tonight I'll try to read the engine codes and will run the car with hood open in the dark to look for arcing. Any other things I should try to do?

We bought the car last year from a dealer in a neighboring state at 90 k miles, and had major service performed then.

Thanks

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

My money is on a code 5 - egr system inoperative - stuck egr valve. Let us know what code you get.

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Jim

We checked and rechecked the fault codes--got 6 (idle speed control inop.) and 7 (ignition system failure). Couldn't see any sparks in the dark (confirming what someone wrote me--thanks!). I tried to find relevant information on the Benz 124 CD without luck. I forgot to mention that I washed the engine (mainly its underside) a month ago to remove widespread oil (apparently leaking from the timing chain cover--front right of the engine).

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

Try cleaning the idle speed control motor and check for vacuum leaks.

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95 E320 Cabriolet, 159K

I'm not 100% sure, but I don't believe his model has an idle speed controller like '92 and earlier 300E's.

His model has a throttle actuator, which has several functions, idle speed control being one of them.

Certainly does sound like a vacuum leak. I'd recheck all vacuum hoses to make sure they are attached and not cracked.

I'd also check the spark plug ends on the three coil wires. You could have a misfiring cylinder.

Remember that you have three coil wires and three spark plug wires, and they rarely go bad. The failure is usually in the boots or ends of the wires. They are about $7 each.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

You also could have a defective mass air flow sensor, which works with the computer and throttle actuator in controlling idle speed.

Typically, though, a failing mass air flow sensor would show itself with an oscillating idle going up and down.

A vacuum leak will also make the throttle actuator and / or mass air sensor work improperly.

If you have a vacuum leak, it could also be at the intake manifold seal. You can spray water at the gasket to see if air is leaking there.

My intake manifold gasket failed causing a vacuum leak that caused me to replace both the actuator and mass air sensor. The bad idle remained after two indie MB mechanics failed to find the vacuum leak.

I took it to the dealer, and it took them 30 minutes to find the leak at the intake manifold.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I missed - that egr pluggage is so common at certain miles I just took a guess.

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Jim

I would've guessed the same thing that the egr valve was stuck in the open position.

You can't win them all...

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

One of the cool features of these late OBDI systems is that,
with the aid of a $5 homemade led/tool [ archieves], one can get plenty of further diagnostic info from the systems specific modules through the other sockets on the DTC box.
Case in point , using this thread as an example, CE emissions code #7 ignition fault can now be expanded upon by going right to the ignition diagnostic module [ pin #8] and get more specific info... like "Plug mis-fire, cyl # 4" , etc.
Example two-- CE code #6 can be refined by going to the ISC/CC/IA module at pin #14..

Anyone with these systems should def. look into making the tool...these DTC were quite good for the time and have plenty of info that is accessible ....
After these models , one can't do this anymore as the systems are OBII, so feel fortunate and make the tool....

The ISC/CC/IA that Arthur refers to are the functions controlled by the throttle actuator.

Just thought I'd put that in.... (free. no charge to the reader).

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

First I will look for loose or cracked vacuum lines. I hope they are easy to find (clear or white, right?) I saw a post in the archives about testing for vacuum leaks with starting fluid. Seems that since I might have ignition leaks, I'd better pass on that method.

Next I'll check out the coil dealie spark plug ends. I found a post listing old part # 000 159 35 42 and new part # 000 159 36 42 . Does this sound right?

I'm intrigued by Dalton's suggestion to make a $5 diagnostic tool. I found a post by stevebfl (06-10-2000 07:35 pm) where he wires a diode between the battery pos and the diagnostic socket in question. But he ends by warning that "One should not do this unless you have appropriate service info to use the results and understand the system." (I guess that since I can't even find a decent diagram of the car's engine that rules me out.)

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

I pulled codes the other night. Code 6 (Idle speed control inoperative) and Code 7 (Ignition system failure) To read the detailed codes I built Arthur Dalton's very cool code reading tool this morning. Parts now cost $8 at Radio Shack. With expert coaching, I got code 23 off Pin 8, indicating the resistor boots under the coils are at fault. (Also got codes 3 and 14 off Pin 14, which I'm told could be related to the coils). I am now waiting for parts.

I can't believe how easy the codes are to read!! Thanks again, especially to Arthur.

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

I had the same problem on my S 320. after washing the underside of engine, to later check for oil leak.

One day later while parked against the curb with engine running, the car jumps into a rough idle mode.?????. Thought maybe some water was in the spark plug well ???.

Problem was a dead (completely dead) spark plug. changed all spark plugs the car runs better than before.

I replaced the 3 boots and 6 plugs last night--old gaps were 1mm. I reset all codes. (Bad news: the well down to #6 plug, under the coil, had a liberal coating of orange powder. Rust?? Maybe water somehow backs up into the trough from the rear of the engine and goes down the well.) Anyway, it idled better but not perfect and missed erratically under accel. I put in a bottle of techron and filled tank this am and did my best to give it an Italian tuneup on the 30-mile commute to work. Runs fine cruising and above 4000rpms. Seems to accelerate a bit better now but still misses irregularly at idle. The check engine light did NOT come back on. So, could it be bad plug wires, the other 3 resistors at end of plug wires, bad coil, or crud in the throttle body (pretty icky down there) or the egr valve? Is there an easy way to remove the throttle body from under the manifold? Thanks!!

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TomO
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)

Yes, what you are referring to as the "throttle body" is really the throttle actuator, and it can be removed without taking out the intake manifold.

However, from reading your posts again, I do not think your actuator is bad.

I can't believe that all of us missed it, but you have a '94 E320, and your problem jumps out at me like you have a bad engine wiring harness.

All of the engine wiring harnesses from '93 to '95 on these M104 engines have bad insulation that cracks with age, causing random check engine lights, mis-firing, poor idleing, hesitation under acceleration, etc. You have all of the symptoms.

There was even one post today about an idle problem and the culprit was a bad wiring harness.

I did a search and here are the results:

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=236309&sortby=lastpost&sortorder=descending

Go ahead and read through as many of the posts as you can bear, and let us know what you think. There are ways to check the harness and you will find this in many of the threads.

Good luck.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".