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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53904
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Hard starting and rough idle. I did new wires dis. caps,

Customer Question

hard starting and rough idle. I did new wires dis. caps, plugs rotors to start but there was no difference
JA: Is the rough idle intermittent or consistent?
Customer: It drives smooth, but takes awhile for it to clean out. I have not done a com. test because it only has 80000 on it and didn't think it needed it.
JA: What is the model of your '78000 Mercedes?
Customer: 1992 SL500
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Just a complete tune up minus a fuel filter. All wires, plugs, rotors etc.
JA: Anything else you think the mechanic should know?
Customer: We just bought the car so I don't know of anything else
Submitted: 10 months ago.
Category: Mercedes
Expert:  Marty replied 10 months ago.

Hi, my name is***** overvoltage protection relay located in the right rear corner of the engine compartment powers the cold starting system and the fuel mixture control. If the relay is bad or the fuse in the top of the relay is blown the car will be hard to start and will not run well until it warms up. Click on the attachment below for the relay location. You can barely see it in the picture. It sits down behind the silver relay with the block knob on top of it.

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