I have a 1991 300 te 4 matic wagon with 112,000 miles on it. When I try to start when engine is cold, it may take 5 to 10 minutes to get the car started. After car starts it runs rough until the engine warms up. I have replaced plugs, wires, and cap and rotor but no help. Any suggestions? I was told it could be the OVP relay or the cold start injector.

The fuel computer must en richen the mixture for cold start to happen!

The over voltage relay has to power the fuel computer, start there.

First check the fuses in the over voltage relay (10A ATC) behind battery.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
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I just dealt with the same situation. My problem appears to have been with the fuel computer. So far and I mean only since yesterday does my very, very hard to start situation seem to be cured. This morning car turn over and started as it should.

You should follow M.B. DOC's test procedure and not assume your problem is same as mine.

Over voltage relay MUST supply to the computer first.

Don't start by replacing a $$$$ computer.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Caveat: My experience is with a 1988 560SL.

By all means do what Doc said. If no fix, before throwing expensive parts at it, check operation of the engine temperature sensor that inputs to the computer. That sensor is a simple screw-in replacement and costs in the neighborhood of $45 to $60. Available here on FASTLANE from Phil.