My 93 300E2.8 has developed a bad stumble/misfire at idle and when initially accelerating. At speed, it seems fine, has plenty of power and does not miss. The check engine light is not on but when looking at the codes at the connector underneath the hood, I get a "7" which I think means ignition failure. Plugs were changed about 2000 miles ago (ran fine until about 50 miles ago) and looking at a plug I took out, it seemed fine. What would be the things to look at for this problem?

One or more ignition coils (you have 3). Don't know if they send out an error code when they do fail...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Are the new plugs Plats.??

These engines like the copper.

They are for sure copper but I had a hard time convincing them to sell them to me. Everyone wanted to sell me the platinums.

I suspected the coils but I do not know if they will signal an error code. I was surprised that the "check engine" light was not on as well but I do not know what all turns it on.

You may want to check the coil tower spring connectors.
Also , may have the old wire harness [bad insulation]
Any code that comes up on the led/sw combo is emmission system related and will eventually bring up the ck eng lamp.
There are codes on the other connectors that will narrow down the coils. [ pins 8 and 14.] But you neeed a code retrival tool/scanner for that.

i follow your problem reports closely as our cars are the same model year and approx mileage. you haven't had the harness changed right? from what i've learned i would pick the harness rather than the coils to be the culprit. i remember your saying you've had it since new so maybe you can get the dealer to do a goodwill replacement...

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joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
http://banners.wunderground.com/bann...L/Key_West.gif

I have examined the harness carefully where the wiring is exposed and so far, I have seen no signs of failing insulation. It might be there but I cannot see any signs of it. Worth another look though. And I do have an appointment next week at the dealer I bought the car from. The appointment is for something else but I will have them check if I cannot figure it out before then.

Forgot about the wiring harness...it was found to be the source of my 300E having the same problems as yours.

As far as being able to detect a bad harness just by looking at it, here's a thread you might want to check out:

Wiring Harness pictures

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

my car had similar intermittent rough idling / stumbling immediately after the hg job. the only clue was that after touching one of the leads to the injectors it smoothed out. i should perform an autopsy on my harness as it looks perfectly fine except where my local indy tried to see what was wrong with the leads - there you can see large sections of wire are bare. that section that steve opened up in the picture goes underneath the intake manifold and has the leads to the injectors...

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joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
http://banners.wunderground.com/bann...L/Key_West.gif

Looks like my problem is fixed. I ordered both a new coil and the rubber boots at the bottom of the coil. (Fast Lane got them to me in record time--overnight was truly overnight!) After a little swapping to find the bad one, everything seems OK again. Perhaps I just moved the "bad" wiring enough to get it to working again but so far but I assume everything is fixed.

The rubber boot is the coil tower spring I referred to.
I had to change a couple of them for the same problem,
so you may want to replace all three.

Pfphipps,
How many miles now? Gotta make a note on this "error code 7 =? coils". Don't move that harness any more than you have to...
Cheers

__________________
joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
http://banners.wunderground.com/bann...L/Key_West.gif

I replaced one coil and all three of the boots so I should be OK there.

In answer to the other question, I have 73,000 miles on the car. I did not move any harness at all other than just incidental movement to put on the parts I described.