I hope you'll bear with me but my problem goes like this:

About three months ago, I had a local shop, who does only mercedes benz's, repair my long-running problem with the oil leak and noisy vibrations caused by a bracket connected to the airconditioning compressor. They installed new oil seals and removed all broken bolts of the bracket and replaced it with a new and sturdier type. This were all done with the engine out of the engine bay. After, all were done, they returned the engine and did the regular oil change and tune-up.

The repair was well done since no leaks and noisy vibrations ever recurred after that.

However, I suddently developed a hard starting problem. I returned it to the repair shop and they adjusted fuel and air mixture, etc., and somehow concluded that my starter is failing. It soon did fail and I immediately replaced it.

The replacement cured the hard starting but it returned after a week. Next I had the injectors cleaned. That was fine but the hard starting returned. To save the effort and money, I just adjusted my style and started the engine while softly pressing on the gas pedal. That was fine for a while. Last November, my aux fan relay got burnt. That was replaced, but electricity seemed to fluctuate. Tapped the OVP and secured the new relay upon the advise of my electrician. It worked.

One December morning, apart from the hard starts, I suddenly encountered, a very rough idle at start up. So rough that the engine will cut off whenever I turn on the airconditioning or release the gas pedal. This somewhat normalizes when the engine gets warm. I say somewhat, because it is still not a perfect idle because there's an occassional shudder that I feel. Cruising, though is not a problem.

I sent this to another shop (mercedes benz only) for tune-up. They changed the spark plug and adjusted fuel and air mixture. They cannot get the idling to run perfectly as it should. They came up with the conclusion that the control unit should be replaced by putting another unit.

Because it was expensive, I tried to get a second opinion. I found a shop who said they can diagnose a bad or good control unit. They did not see anything wrong with it. I don't know if I was glad to know that there's nothing wrong or was just glad that they said what I wanted to hear. They did, however, cure my stumbling idle at start up by increasing idle speed which the previous shop said they cannot adjust because of the control unit. But there is still the hard starts and occassional shudder even when the engine in under normal operating temp. They said that the occasssional shudder might be the engine support. But I replaced this about 3 years ago. Do engine supports fail within that period?

This is still bearable but can anyone please point me in the right direction. If it is indeed the control unit (ouch!!), there goes my money for the paint job. I've checked the OVP and the fuse seems fine. I've read, though, that they can fail internally. I'm not a technical person. so an explanation on what my problem (causes/solutions) in layman's terms will be appreciated.