Hi, first time here, but hopefully someone can help.

I bought a 91 420SEL. The problem is that on the first start of the day,
it doesn't seem to want to catch, just turns over and over until finally
it fires, then takes a while to get running. Once running it idles higher
than it should.

Starts fine if it doesn't have to sit too long. Starts easier when the weather is warmer, takes longer when weather is cold.

I've been told to replace any number of things from the oxygen sensor,
to ignition sensors, to it's a valve problem.

Simply want an idea of what is the most likely culprit, don't have cash to
experiment with solutions.

Any help is greatly appreciated.

Thanks.

ABS lamp ON ???

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A Dalton

Yes, it's been on since I bought the car.

Check the fuse on top of the OVP relay.........

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A Dalton

Arthur, I will do that first thing tomorrow. That makes so much
sense, amazing all the "experts" I talked to didn't think of that.

A fuse....at worse, the relay.

Thanks.


(now if I can find it.....)

Arthur....dead on. Replaced the fuse, car starts right up on first turn.

Idles waivering a bit, but 10 times better than before.

Thanks, you saved me a bunch of time and money.

Very Good.........

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A Dalton

so... what does the fuse on top of the OVP relay control that would cause hard start/rough idle? also, what does OVP stand for? Thanks.

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1987 420 SEL | 87k miles
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OVP is OverVoltage Protection. It's a relay with a fuse on top of the can. It is designed to protect the electronic gizmos such as the ABS computer and the engine management computer(s) if the alternator runs away and produces too high of voltage, or voltage spikes from jump starting.

The OVP relay has a bad habit of going bad in random and intermittent ways. When troubleshooting anything that seems flaky or intermittent, the OVP is something that should be replaced. In a Gen II W126, a clue your OVP relay is inoperative is an ABS light that won't clear or flicks on and off as you drive.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)