500E rough idle pt. 2 Help! - PeachParts Mercedes-Benz Forum

tom woolner · #1 03-29-2003, 01:38 AM

Registered: Dec 2001
Location: SF Bay Area
Posts: 221 Rough idle 500E pt. 2 Help!

Guys, I need some help. I noticed that my 92 had begun to idle a bit roughly, and mpg was dropping. My tech thought it might be throttle body or air mass sensor, because there was a stored code of "17" but sent me to the dealer, who said, without checking the computer, that it was caps and rotors (caps corroded). So, I spent the money, then noticed virtually no difference. While waiting for my next appt. to take it back, I lost a huge amt. of torque, took it to my tech, where we realized that the dealer had misrouted the coil wire, and it had worn all the insulation off by rubbing against the power steering pump. (no doubt trying to beat the flat rate). The dealer begrudgingly replaced the coil wire, Friday, 5 o'clock. As I drove away, I noticed that it was worse than ever, that now was it not only running rough at idle, but it seemed to have a miss, and noticably stumbles and loses power when taking off. I refuse to go back to the dealer (RAB in marin co., CA), and my tech says the next step is throttle body/air mass sensor, which my warrantry won't cover.

1) Before I start throwing parts and $$, is there a way to find out before buying those parts if that's the solution?
2) Could the burnt coil wire have caused any damage which is making it miss more than before?
What should I look for?

I'm frustrated, and writing a letter to MBUSA, since this is the fourth incident of damage done to my car through carelessness.

Tom
92 500E

Report this post to a moderator | IP: Logged

03-29-2003 06:36 AM

stevebfl · #2 03-29-2003, 10:26 AM

A lot about this post confuses me, but maybe its because I didn't see part one.

My simple answer is that testing is required to keep from buying parts. Looks like the dealer won't do it. This is where it gets difficult. This is sorta like Catch 22. The dealer has diagnostic test equipment but doesn't pay techs for using it. So they don't(This is established in warrantee work and becomes a way of life for dealer techs - in general - we obviously have at least one on this site that breaks all those rules). Independents seldom have all the necessary tooling and usually don't have the training = big problem.

This would all change if techs got paid what it was worth to do this kind of work. The only problem is that techs get paid what the market will bear. Thus it is very unlikely that your problem will get the necessary attention most of the time.

You are better off needing a waterpump, but then again you probably would DTY (do that yourself). The tech that does the waterpump will make a lot more than the tech that fixes this problem. That is the real problem!!!

vcci · #3 03-29-2003, 08:22 PM

Personally I would go back to the dealer and demand for the to either.

1. Figure out the problem, fix it and deduct the amount of money you spent on useless parts they recommended to be replaced from te your new invoice.
2. Find your old caps and rotors and give you back your money, because obviously your old ones were good.

At least you wont be out a few hundred dollars for parts you never needed. I would take it to the highest Mercedes Authorities, someone must realize they made a mistake.

Good Luck

tom woolner · #4 03-30-2003, 01:24 AM

I will not let that dealer touch it again. I would rather eat my losses rthan allow them to get near any car of mine again.

aldedmon · #5 03-30-2003, 02:28 AM

Tom, Have you / they check for a vacuum leak in/around the intake area. Those little plastic tubing hoses get brittle and break at your mileage/earlier. Check those bad boys and then check the rubber "sleeves" that hold the upper/lower halves of the intake together byy spraying brake CLEANER all around the intake near but NOT into the plenum. Go ahead (protect your fenders and underhood painted areas, cause this **** will F/U your paint) spray away. if the car dies/changes idle or does anything but run normally....you got a vacuum leak. narrow it down by duplicating with the spray until you pinpoint the offending area. On my 400E ,I had to do this last year(replaced all the tubing and the "sleeves") and then I had my injector flushed and now she runs like a top...smooth idle. Tell me this is she missing (for instance when you drive first thing)or just idling roughly. mine was idling roughly and missing like all get out for the first few miles till warm

tom woolner · #6 03-30-2003, 02:48 AM

Albert,
Thanks for taking the time to help.
Mine is idling roughly, missing, and running roughly as I pull away. it does not stop after getting warm.

Tom

pentoman · #7 03-30-2003, 07:37 AM

That is just dreadful service by that dealer. The only point in going to a dealer here is, because they have a large Mercedes sign outside. But it seems, they don't want to fix your car, they just want to get rid of you.

IMO, Find a good independant who wants your business and wants to spend the time to fix your car.

RPM55 · #8 03-30-2003, 08:50 AM

The most common cause of rough idle and running complaints on this engine is corroded distributor caps and rotor buttons. It seems the dealer was going for the quick easy fix, and was in too much of a hurry to get it out the door thus not seeing that the coil wire was not routed properly. If the caps were indeed corroded and green looking inside then they did need to be replaced and may have been part of your running problem but not the only cause. Other possible causes are a bad engine wiring harness,i.e. insulation cracking.I have also seen throttle actuators cause problems as well, the insulation cracks and causes shorts just like on the engine wiring harness.
I would suggest having your tech cut open the harness on the throttle body to inspect the wires inside. If the insulation is cracking then you are going to need a new throttle body.
The air mass sensors do cause running problems but dont usually cause a rough idle. Not knowing the service history of the car the problem could be as simple as a faulty spark plug or a faulty resisitor end on a spark plug wire.

TimFreeh · #9 03-30-2003, 09:37 AM

Check your engine wiring harness. My 93 400E was exhibiting the exact same symptoms and when I inspected the wiring harness I could not believe the engine would even run -many wires had 4-5 inch lengths of insulation totaly gone.

A new harness totally solved my idle problem. The car now idles at 550 RPM smooth as a V8 should.

A properly running M119 engine is a joy to behold - very strong power at any RPM and 22-24 MPG on the road. Who could ask for more?

Tim

suginami · #10 03-30-2003, 03:08 PM

Is it too much trouble to bring your car down to Mr. MB Motors in Tarzana, CA?

There are a lot of high fives about Enrique's shop and his level of expertise in the Good Shops Forum.

He is I guess in his middle 50's, and has been working on Mercedes cars at Mercedes dealers since he was 18 years old, first in Spain (where he was born and raised), then Argentina, then South Africa, and finally at two Mercedes dealers in California - the one in the San Fernando Valley, and the dealer in Beverly Hills. He has operated his own shop for about the past years.

I was just there again last Thursday, and the local Mercedes dealer brought in an R129 SL500 that they couldn't diagnose and asked Enrique to take a stab at it.

I couldn't believe it! Enrique says they bring in cars from time to time that even their best techs can't handle.

Here's the deal on that car - the car was pinging real bad, and the dealer assumed it was a burned valve, but after taking the head off, found that the valves were fine.

While I was waiting in the shop, Enrique checked the timing of the valves and found that it was not right. Apparently, a previous mechanic had done a timing chain on this engine, and left off the woodruff key! The key goes in the crankshaft. The timing chain connects to the crankshaft via a sproket that slides over the crankshaft. This sproket is held in alignment by a woodruff key. They make more keys that slightly offset this gear a few degrees which you could effectively advance and retard camshaft timing, or if it makes it more clear, retard or advance crankshaft timing.

Anyway, Enrique was laughing to himself at the end of the day when he discovered this. He was originally the Shop Foreman at the dealer, and he told me that out of the 38 technicians they have there, maybe 2 are really good. That's right, just 2.

And the good thing about Enrique, is that he has all the parts and all the diagnostic equipment, and he never replaces parts willy-nilly when troubleshooting a problem. Diagnosing problems requires testing, and that above mentioned SL 500, I popped my head in while he was troubleshooting it, and he was explaining to me all the things he had tested before finding the problem was the woodruff key.

tom woolner · #11 03-30-2003, 03:36 PM

It's too far to go, I live in the Bay Area. I like my tech, so I will continue to work with him, going from the less expensive to the more expensive. I appreciate all the suggestions as to what it might be, so that I can rule them out, again, going from the east $$ on up. The service records i have are a bit spotty about the 90,000 service, so it might be something like a spark plug or resistor.
My question, though
Could the missing have anything to do with the coil wire shorting out? it was not missing, although running rough, until the coiol wire shorted out.

Tom

vcci · #12 03-30-2003, 03:56 PM

I personally wouldnt trust Mr MB Motors, I went down there when I couldnt figure out why my car goes into " LIMP MODE". He started looking at it and was going to put it on the scanner, but when he looked at the plug where the scanner hooks up to, he said my car is missing some pins. That really got me thinking, so I go back to work and later that day I take a look at my buddy's 94 E500 ad sure enough his is the exact same way, same number of pins. now I start wondering, both cars are the same why would he tell me it's not normal so I take a look at another 92 500E and guess what, same number of pins. I heard a few people say good things but from my personal experience, he doest know JACK. But I could be wrong. If I have any problems from now on I would only go to Carl @ BergWerks, he seems to know these cars very well.
Just my 2 cents

stevebfl · #13 03-30-2003, 04:08 PM

The 92 federal models don't have a DM (diagnostic module) and that may through a Ca tech which had them on everything since atleast 90.

Just as I don't see sainthood in a single moment of genius, I also don't fault one for lack of data retention; that's what books are for.