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Old 05-19-2013, 01:30 PM   #1 (permalink)
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Post Missing, hesitating misfire at slow speeds

I had my '92 500 SL into my mechanic last week for a recurring missing and hesitation and rough idle problem. I wanted him to replace the distributer caps, rotors and spark plugs in the hopes that would cure the problem.

When I picked it up he had replaced a vacuum hose and said that the car needed to be driven more to keep it in shape (It only gets driven about 500 miles a year), and that the other stuff wasn't needed. I did notice that it was idling smoother and seemed to have more power. I thought great, saved about $400!

Got the car out this morning and yes, all of the old symptoms are back with the exception of the rough idle. He suggested a bottle of techron fuel injector cleaner and some hard driving.

I put in a bottle of the techron and drove the hell out of it! The hesitation really is major. It misfires and drags until about 25 MPH then it kicks in and jolts so fast it even makes the drive belt scream!

Should I just take it back and DEMAND that he change the ignition parts or do you think he's right and just need to drive it more?

Thanks for your help!
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Old 05-19-2013, 02:35 PM   #2 (permalink)
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Anyone?
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Old 05-19-2013, 03:08 PM   #3 (permalink)
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How does the car idle?
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Old 05-19-2013, 03:13 PM   #4 (permalink)
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well before the vacuum hose was replaced it was really bad, almost to the point of stalling out. Now it idles ok but it hesitates and bucks at low speeds above 25 MPH its fine
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Old 05-19-2013, 03:24 PM   #5 (permalink)
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It actually started last summer. I had 3 heart attacks and a stroke and was in hospital for two months and then couldn't drive for another 2 months so the car sat from May until September. The problems started then but have gotten worse lately.

It didn't affect my S class though

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Old 05-20-2013, 08:45 AM   #6 (permalink)
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I'd consider checking out the fuel pressure regulator. I was told that was a possible cause for rough idle. Mine has a rough idle at low rpm that a dealer and indy have both attributed to intake manifold leak(s).I also replaced all the rubber air lines to the injectors and to the idle control valve. If it's only rough at low rpm, I would start by checking the fuel and air intake system before more of the vacuum or ignition systems (my personal opinion). Hope this helps; I've been trying to get my idle perfect for a couple months now, and I know how frustrating it can be.
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