Will do. That's the thing that seems so elusive about this problem... you fix one thing and it IMPROVES the issue, but doesn't resolve it. It seems as though there's almost no definitive solution out there...

Just talked to the mechanic... He's had the car for more than 3 full days and can't figure out the problem.

He swapped out the EZL unit from the other car and the problem persisted all the same. So in a way that's good news, cuz the EZL's are offensively expensive.

So the next theory is the catalytic converter. Since this idle problem has persisted since even before I had my head gasket and valve job done (due to leak down in one of the cylinders), my hunch is that too much gunk was getting into the catalytic converter... that would also explain the poor emissions. The mechanic said the way he'd test it is by disconnecting the headers or something so that there is at least a 1/2" gap and running the car, thus removing the cat from the equation.

I suppose I could do that myself. But is that a bad idea?? It just sounds dangerous, I dunno. Opinions please!

Bigpete. I have a 1991 300CE and a 1989 300TE so I am following your thread with great interest.

If you try to disconnect the cat converter and related parts just remember that it gets very hot in that area and that you are dealing with potentially lethal exhausts, so make sure that you have plenty of ventilation.

Thanks for posting.

__________________
Current Benzes

1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

Res non semper sunt quae esse videntur

My Gallery

Not in this weather!

I'm glad somebody's reading this thread!!

I'm extremely discouraged by this whole experience. I thought I was going to be buying a virtually maintenance-free car 3 1/2 years ago. Non-routine maintenance has cost me over $12k since I bought it... and I still have this ridiculous idle problem.

Is there anything wrong with replacing the MB cat with a generic one that will fit my car? For example:

http://www.discountconverter.com/converters/display_table_cylinders.cfm

That comes in at roughly half the price of the OEM version.

I have an '88 300CE and had a similar problem. My mechanic replaced the overcharge relay and bingo, idle was smooth as silk and acceleration is smooth. It even sounds completely different. It probably didn't hurt that I got a new camshaft and rockers, but I really think it was the overcharge relay. Our E300 also had rough idle and start problems and the mechanic resoldered two lines on the cold start relay and that immediately took care of those problems for good.

Man, I feel your pain. A few years back our 300TE developed a sudden stall problem. I went through 3 mechanics and none could figure out the problem. Finally Enrique of Mr. MB Motors (So. Cal.) figured out the problem.

If he had not figured out the problem I would have dumped the car.

Hnag in there!

__________________
Current Benzes

1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

Res non semper sunt quae esse videntur

My Gallery

Not in this weather!

Yeah... It would be nice if it was as simple as something like resoldering some wires. But it seems like those kinds of causes are very difficult to find.

Remotemark, are you referring to the over voltage protection relay, or "overload relay"? Cuz I pretty much just swapped that out.

I got the car back this weekend. The mechanic had the car for 4 full days and only put 3.5 hours into it. Very frustrating... they need to learn how to use a schedule. They ran some tests as I discussed earlier... Changed the plugs and adjusted emissions... the exhaust smells less rich, and the car is running very smoothly. I'm pretty sure the problem will come back though. It always does this after the plugs are changed... runs smoothly, then goes back to its old ways within like 100 miles.

Maybe I should just keep changing the plugs instead of taking it to the mechanic!!

Big Pete - it was the over voltage protection relay, which doesn't necessarily compute to idle problems or smooth running, I know. I had been to several indy repair shops who replaced countless plugs, wires, caps, adjusted mixtures, replaced valve seals, etc., nothing of which helped. Finally I found a guy who lives and breathes these cars and he just listened to it for a few minutes each time and then seemed to know where to look. It was an 18 month saga and cost me a lot. Luckily for my panzer, I like it too much to give up on it because of something silly like half a year's pay.

I just recently dealt with the same issue on a 1990 300SL. After replacing several unnecessary parts, I found a loose clamp on the connection between the two halves of the Intake manifold. Tightened it up, reset the computer and it runs like new

so far, the hesitation and rough idle are 90% better but still present... again, I'm planning on having the problem come back again.

I might have a shop check my catalytic converter if the problem comes back in full force (my exhaust still smells rich), but if it doesn't, I'm just going to except the fact that my car is old (200k miles) and is never going to run like new without some major work... so if I can get another 50k out of this car without major maintenance even if it has a crappy idle, so be it... As of now, I probably only drive 7k per year, which will get me 6 or 7 more years out of her... then I'll buy a reliable, low-maintenance japanese or Korean car... I never thought I'd say those words...

Hang in there Bigpete123,
So far you've mentioned the repairs I've done (and the repairs I intend to do) on my E320 of the exact same problem. Because of that, I just saved tons of money. Seriously, thank you very much sir.
I don't have much to share with you regarding the repairs I've had done because you've already done more than I have. Truth is, I'm just waiting for the outcome of your catcon replacement. Please post the results of that as I, too, am just about ready to give up and buy a low-maintenance Japanese car.