My 1993 400E is stumbling/ running rough at mid throttle. It starts up and idles fine. It seems to run well when the engine is cold, but problems show up when it is warmed up.

I checked for DTC's with my Trisco/ Palm scanner, and found no engine codes set. (I did discover an ABS code, but I haven't tracked it down yet. My wife isn't currently driving the thing until I get the running rough part fixed. She's taken over my Tundra Double Cab until I sort this out... One of the sensors for the front wheels is dead, apparently... As soon as I fix the engine, I will track the ABS problem down.)

It seemed to be a lean miss, so I immediately suspected the EGR valve opening too far or too soon. The problem only occurs at mid throttle, and the EGR is out of the loop at idle and full throttle... Replacing the EGR didn't cure it, though.

The fuel pumps, spark plugs, caps and rotors, oxygen sensor and EGR valve are all new, or new in the last three months. All were replaced with Bosch parts (except the EGR, it was a Pierburg egr valve) most from the dealer. The car runs great except for this mid-throttle miss... I did clean the MAF hot wire with some MAF cleaner... No change... I looked for any kind of vacuum leak, but can't find a thing.

I am at a loss as to what else may be wrong. Maybe one of the coils? I don't know... When the car is climbing a steep hill you can really feel it, on level ground it seems to run pretty well to where it is not really noticeable unless you are looking for it.

What else should I be looking at? The car should be running great like it always has for the last 160,000 miles, but it just doesn't...

sigh...

Somebody please point me in the right direction, I am out of ideas as to what might be wrong with it...

Thanks,

Kelly

1993 Arctic White 400E

How about fuel filter? that will give syptoms such as yours and if it hasnt been done in awhile it needs it. (you didnt mention it) . good luck

Also Have you looked @ the wiring harness? O2?

Jonathan

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+1 on the wiring harness. Have you inspected this? You may need to pull some of the insulation back to really get a clear picture of the condition. That is the first place I'd look... If it's rotten, you can spend money on parts until your blue in the face and may not find the solution...

Good Luck,

-GH

ditto on wiring harness. also maybe ETA.

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Frank
84 500SEL EURO 101K ( JUST LIKE MY 1ST WIFE. GLAD TO GET RID OF HER! )
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)

Circular cracks sometimes form around the soldered pins of the relay circuit board. Usually around the pins of the heavier components mounted to the board. Heat can cause expansion of the board and change of grade (level) can also cause the heavier parts to shift and open a crack thus losing contact and fuel supply.

Open the relay and inspect the back of the board with a magnifying glass. Look for a circular crack in the solder around the pins that protrude through the board.

To repair the relay you can touch up (reset) the solder with a hot iron or you can get a new one from Phil.

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

Sorry, I've been out all day... I guess I'll try to answer everything at once.

The fuel filter was replaced along with the fuel pumps. (They were replaced mainly because one was getting noisy... I didn't expect that to fix the miss problem.

Looking over my post, I may not have been totally clear. The car only misses at certain mid throttle points... It runs great if you floor it, and it starts right up and idles fine. If you baby the throttle around town, you can drive the car with no indication anything is wrong. But when you try to merge on the highway, or drive up a steep hill, the thing stumbles badly. Sometimes very badly, like it won't make it up a couple of really steep hills here in town... Unless you floor it, and then it goes way too fast!

How can I check out the ETA? And why are there no DTC's set? Where can I get the information on testing that? (That's my biggest frustration/thing I hate about this car. The documentation from the manufacturer is horrible. The Factory Service Manual CD's were all but useless... I am used to the Factory Service Manuals from Toyota and Nissan, and those are great books to have when anything goes wrong... In all the years I have had the Mercedes Factory CD's, they were actually useful twice... That's it. Replacing the blower motor and regulator, and a couple handy tips when changing a water pump... Most of the time, I don't even try to look at them anymore... The answer's never there.)

The O2 sensor plugs in to the male connector, and without ripping all the insulation out I can't see the harness. I don't know where it goes, I'd hate to rip out the insulation and find that it just dissapeared immediately anyway. I suspect that it goes right through to join the main trunk line that runs throught the center console, which looks like it has enough wires to wire up the phone system of a small city.

All the wiring in the entire engine compartment looks good, no cracked insulation or other problems that I could see.

Everything looks good, but something ain't right!

If all else fails, does anyone know of a good Mercedes shop in the San Jose, California area that I could take it to for a diagnosis?

Do a search on wiring harness on this site and you will find tons of pictures and info. I just replaced ours on the 93 400E at 99,000 miles. If yours is original that's got to be a record.

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95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

Well, I have just received the wiring harness... I sure hope that fixes this... Looks like I will have something to do tomorrow... Have to get it done before Sunday... Definitely by 1:00, because I will not miss the Patriots/Colts game!

By the way, this car actually has 192,000 miles on it, with virtually no problems to speak of. Almost everything that has ever gone wrong with this car has not been any fault of the car! (For example, my wife loaned it to a friend who managed to drive it almost 30 miles with the park brake set... Hello... Anybody home? What do you call a person too stupid to look at an idiot light?) The parking brakes were interesting, to say the least...

The only thing that has ever broke in the car is the sunroof motor, blower motor and a rear window regulator... Everything else has been simply maintenance... In 192,000 miles, I have only had to replace one taillight bulb and the headlights (Once!)

If it doesn't take too long I will also track down the problem with the ABS sensor, and figure out whether it's the swith or the solenoid that's causing the transmission kickdown to only work intermittently... Time to change the trans filter anyway...

I will post back the results of the harness swap...

Thanks for the help/advice... I appreciate it!

If you want to save some time on the wiring harness, consider threading the individual wires through the hole from the back of the firewall, rather than trying to fit the lever-type connector through the firewall hole. When I did mine, there was a brittle rubber elbow on the back of the valve cover (right side) that got in the way of fitting the connector through the firewall hole from the engine compartment. If I had taken that hose off, it would have cracked for sure. It took me about 45-60 minutes. All that was required was an Allen wrench and a small screwdriver to pry off the old connectors. If you want to be safe, take a picture of how the old wiring harness is routed before you take it off. Good luck.

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

If that doesn't fix it, I would seriously consider looking closer at the ETA.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Replaced the wiring harness Friday night, only took 45 minutes... At night, so if you do it during daylight it would probably only take a half hour or so... When I reconnected the battery, the clock was 45 minutes slow, so that is all it took... Very easy to do, much easier than replacing the plug wires... If you are thinking of replacing your harness, don't sweat it, it's really very easy to do. Typical Mercedes design, you simply cannot plug anything in to the wrong part, the connectors are physically able to only plug in where they are supposed to.

About the only problem; it didn't fix the stumbling!

It does seem to maybe idle a little smoother, but then, it always did idle very smooth. The only problem is I need to replace two plastic clips, since they were completely brittle and broke taking them out, and the new harness didn't come with new ones... The new part was made in Poland, looks to be very good quality... My old harness was VERY brittle, I would be unhappy if I saw this come off a Dodge or a Chevy... Cannot believe it came off a Mercedes... Absolute crap!

The ABS brake code was a EA CAN communications error, not a wheel speed sensor malfunction... So I erased the code, and I will have to see if the code comes back with the new harness. I didn't get a chance to see if the ABS is functioning now, I decided to change the trans fluid and filter, and Napa managed to sell me the wrong part. (They had two different parts listed, and I looked at the pictures... I picked the one that looked like my pan, and he sold me the other one...

I still need to know how the heck I can check out the ETA... I searched through the POS "Factory Service Manual", didn't see anything on it... I have the Mercedes WIS too, but I haven't reinstalled it since I rebuilt my computer. I am not a fan of that software, either... I has a lot more detail than the factory service manual, but it's such a struggle to find it... The only thing I liked about the Workshop Information System is the screensaver it adds to the windows logon...

I guess I'll search the forums here and see if I can find any info... The server was down this weekend...

Kelly

Once you have removed the ETA, there is a cover on the one side, held on by screws. If you take that cover off, you should be able to see a small circuit board and some wires.
IF...you are going to remove the ETA for inspection, order a new gasket first, as well as the molded rubber hose that sits towards the firewall. Might want to get some of that plastic vacuum line as well. (get 2 gaskets, just in case)

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

How much did the harness set you back? Sorry it didn't fix the immediate problem, but you'll be better off...

Getting ready to do this myself. What is the extent of your mechanical knowledge/experience?

-GH

Bad news - there are two wiring harnesses - the upper one that you replaced and the lower one that's still crumbling and causing problems. When I bought my wife's '95 E420 I wrote a new harness into the deal (at an MB Dealership). They replaced the upper one and the CEL was back on within 20 miles. Because I'd bought it out of town, I ended up taking it to a second dealer closer to home. They ended up replacing the lower harness and the ETA. That fixed the problem for a year or so, then the ETA control module went south and it's new now too.

There's lots of info on this board and at JimF's site about troubleshooting an ETA. The CAN comm error is a bad sign; I got really used to seeing it during the process of getting my wife's car fixed.