My mechanic has been working on my 1992 500sl off and on for about 2 years for a rough idle problem. He never seems to pinpoint the problem after 4 trips to him and $3,200 of work. He's done everything to the car except fix the original problem.

I needed a smog test and he said "I'll fix it so it will pass smog but it will run rough. Bring it back and I'll tweak it so it will run smoother". That should have been my first red flag.

Well it passed the smog test and he was right. It's rough. I bought it back to him so he could fix the problem. He never mentioned that there are smog and repair stations.

I've been patient until last week ( I'm a little slow) after he had the car for 2 weeks andafter the smog test I unexpected dropped by his shop and asked him what the problem was.

His reply:

" Bad gas is your problem"

I lost my cool at this point. This problem has been going on for 2 years. How could this happen. I think he was out of answers and said this in a last resort instead of being honest and admitting he dosen't have a clue what's wrong. What do you guys think about the treatment I'm getting?

 

Find a new dealer or a good indy. this guy took way to much money from you gave you to many bs answers. IMO i would have told him to pound sand after the 3rd attempt and went some where else.

 

The problem could be simple or a little complex. The first thing I would do is add a can of Chevron Techron in the gas tank. It will clean out the injectors and intake combustion chamber.
Add it when the tank is almost empty, and then add Shell or Sunoco high test.

 

Livefree and Paddle.. Thanks for your responses. I'm thinking of telling him to pound sand since the "bad gas" excuse. I've tried the Techron gas treatment but the mechanic says it takes time to work and maybe 500 miles.

So according to his logic , I got bad gas 2 years ago and it's still screwing up my car. Dosen't make sense to me.

 

Does engine runs rough at higher rpm also ? if not it could be dirty injectorsor needs the fuel mixture adjusted

 

If it's not misfiring and just feels rough it could bemotor mounts.

 

Set the parking brake, and keep your foot on the brake pedal. Have a helper observe the engine while you give it gas. If the engine starts to rise, the problem would probably be the motor mounts. Also check the upper shock bushings.

 

Thanks everybodyyou all for your help. The problem is now fixed after 2 years. I can't pinpoint exactly what the problem was since the mechanic replaced just about everything. He told me to add Techron every tankfull and after 500 miles of driving it should get even better.