My 190E has been idling rough and hesitating when I accelerate. I took it in last month for a tune up, new fuel filter, new air filter, new rotor, and a fuel injector service. That helped for a little while and then the same problem came back. In the mean time I had to have the catalytic converter replaced and another tune up. At tune up #2 the mechanic told me I needed new spark plug wires and that would take care of my problem. I put the new plug wires on and it's still just as bad as ever. Tonight while I was sitting at a stop light I noticed that my oil gauge was fluctuating in time with the rough idle and while taking a turn on a steep hill the engine started to cut out.

I've spent $1,070 on car repairs and diagnostics since the beginning of December (my wallet can't take anymore of this) and I'm getting really discouraged because it seems like I'll never get this car running right.

I know there could be a million and one causes for the problems that I'm having.

Ideas?

maybe yu just need new spark plugs! sorry i have a diesel try that first. could be PCV valve or O2 sensor.

Perhaps you may want to try another shop. It sounds like your tech is throwing everything including the kitchen sink into this car and hoping for a solution, instead of attempting to properly diagnose the problem.

A few things come to mind:

1. Is the engine burning oil? Do you see any oil on the plugs? It may need valve work.

2. Was the coil wire swapped out along with the plug wires?

3. The air flow sensor (I forget the correct term, it's in the intake by the fuel distributor, inboard of the circular sensor plate) could be worn out or dirty. Try spraying some air intake cleaner (the stuff for fuel injected engines, not carb engines) up in that area to clean it off. May also want to clean up the electrical contacts/plugs in the engine bay as well.

4. Anything amiss when they run a diagnostic check on the engine?

This so called "mechanic" is ripping you off, trying to learn how your car works. Take your car to a authorized BOSCH specialist and have them check it out. This is a typical mixture problem that you are having and as you very well said can have a million and one causes. It needs to be researched by an experienced Bosch injection specialist.
There is also a small possibility that your timing is off. I assume that it has been checked out already.

Could be a vacuum leak, just start changing hoses. They are cheep and should be done every ten years or so anyway.

From reading the sequence of events, it appears to me that the plugs were fouled because of the bad plug wires or other ignition weakness. The plug wires may have been the cause of the fouled plugs, but if he did not screw in fresh plugs when he replaced the plug wires, then the bad plugs are still in there causing problems.

Did he change the plugs when he changed the plug wires?

Best of luck,

Very unfortunate circumstances. Your next technician will really be working under the gun, with you having already spent at least enough to fix the problem.

I agree that a Bosch Service Center will have the proper tooling to analyze your situation. (that doesn't mean they will use their heads, though, unfortunately). Ultimately your fuel system requires some form of differential flow meter or a lot of experience to diagnose without the parts replacement method currently being used.

I would normally say to stay with the first technician as it is his failure and one shouldn't have to pay for retesting which obviously needs to be done. I don't think from the sweeping proposals (needs plug wires) that real diagnostics are taking place. I have replaced a few sets of plug wires in 27 years but only because the sum total of individual failures and overall condition suggested it. If you have a plug wire failure (or two or whatever) they are easily viewed using secondary ignition scopes.

Your worse case senario is a bad fuel distributor. You need to start with someone that can make such a diagnosis, confidently. (with testing back-up).

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Also make sure those plugs are not platinum plugs!! Mechanics have a nasty habit of putting plats into these cars when they really should have copper plugs.

Lets see, I had new Bosch plugs put in last week when I had it tuned up, I did the plug wires myself the next day. I am going to check for vacuum leaks this weekend and check the fuel distributor as well, if all else fails, I'll spring to take it to an actual MB mechanic have them run some diagnostics on it and do a compression test but I'd much rather try and figure it out myself.

It's not burning oil, I don't see any blue smoke when I start it up in the morning or when I accelerate. It was a quart low when it got tuned up.

I'm stumped. Right now with everything else that's going on, my car has officially been moved to the bottom of the food chain- at least until I've got time to spend dinking around with it.

May be so simple that everybody has overlooked it. I've seen this kind of a problem before. Check out the low voltage wires going to the coil. If these are corroded, then you will have rough running problems. A person I knew years ago went through this exact same thing, where they replaced literally everything electrical and fuel related - except these wires. Her husband later found the bad wires to the coil.