1988 300TE runs fine for 10 min, stumbles for 10 min, then runs fine again...

Hi,
I have an 1988 300TE, it's my second car so it's not driven daily, only on weekends.
Weird problem. The car starts right up and runs fine for ten minutes.
Then the engine starts to idle rough and really shakes the whole car. In stop and go traffic the car will stall but start up again, but it's really hard to prevent the car from stalling when accelerating from a stop. After about ten minutes of rough running, it starts to run fine again.
When it's running fine, it's really running great. Any ideas? It's going to the mechanic this week.
Bob M.
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Does it happen consequently?
In which temperature range does it happen (engine/ambient)?
Bob skrev:

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It's winter in LA, so it's in the sixties during the day and in the forties at night. ~Bob
Jens wrote:

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I meant to say that after 10 minutes the engine is warmed up and the gauge is reading 80 deg C. Locally the weather is in the sixties or higher during the day, and usually in the forties or fifties at night, sometimes warmer. I drove the car today and will drive around the neighborhood for a half hour and see what it does. If I get stranded I'll only be blocks from work.
~Bob
Jens wrote:

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Anyway, if the problem is intermittant, I would suspect the OVP relay or some other electrical failure as also indicated by others.
But if the problem is related to the warming up of the engine, it would probably be in the fuel mixture control. Prime suspects here are the oxygen sensor or the coolant temperature sensor. Or it could be a temperature related leakage in the intake manifold system (inkl. fuel distributor and air mass sensor) or the head gasket (check compression).
I once had similar symptoms in certain temperature/humidity situations (the kind of weather you have now). In that case the problem was a small crack in the ignition coil.
Bob skrev:

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Electrical problem; over voltage protection relay the prime suspect.
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That's interesting. So what is the failure mode. The relay is stuck or being tripped too often? What should I check for? ~Bob
Take A Guess wrote:

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I have an 88 300te also. Had the exact same problem. Put in a new fuel pump relay, which helped somewhat, new fuel filter..no help. I looked at the overload protection relay (ovp) but since the fuse was not blown I figured it was ok. After several days of fooling around with this problem and before the dreaded visit to a mercedes mechanic I found an ovp relay at a junk yard and put it in just to see what would happen.
Immediately, revs when up and engine sounded great. I let the engine get cold and it started right up, had a smooth idle. A bonus is better acceleration and even the ac condensor fan which had not be working sprang to life.
With these type of problems start with the ovp relay even if the fuse is not blown. Oh yeah, my $120 fuel pump relay was not needed, I put the old one back in and it still was running great.
To
"Bob" wrote
> Hi, > > I have an 1988 300TE, it's my second car so it's not driven > daily, only > on weekends. > > Weird problem. The car starts right up and runs fine for ten > minutes. > Then the engine starts to idle rough and really shakes the > whole car. > In stop and go traffic the car will stall but start up again, > but it's > really hard to prevent the car from stalling when accelerating > from a > stop. After about ten minutes of rough running, it starts to > run fine > again. > > When it's running fine, it's really running great. Any ideas? > It's > going to the mechanic this week. > > Bob M.
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