my 300e is having a rough idle when I put the car into drive with the foot on the brake. Do you guys think its the ovp relay? Can someone give me the steps on how to change it. Also what is the part number so I can be sure i get the right one. I already removed the cover behind the battery. What comes next?

Momentum:

If you call Phil at Partshop/fastlane with your VIN number and year, he can get you the correct one. After you removed the cover behind the battery, you will see several small boxes. The OVP is closest to the firewall, and closest to the center of the engine compartment. It has a clear lid on a red top with a blade type fuse on the top. It pulls straight up, and is 'keyed' so that it only goes in one way. The fuse on the top may or may not be blown if the OVP is bad.

The rough idle may not be the OVP (fuel pumps, coil, plugs, wires/points, fuel filter, etc.) You can check the fuse on the OVP and if it is blown it is probably one of your problems, but if it isn't you may not have ruled it out. Check the least expensive things first, and good luck!

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

When you say that the engine is rough, do you mean a shaking engine or can you actually notice a significant drop in RPM?
Just wanted to clarify because you might have bad engine mounts, which would cause a bad vibration when engaged in gear.

Vin

The OVP is the source of hot start problems and can cause stalling while driving, but is not related to rough idle problems...unless, as mentioned earlier, the fuse is blown.

Check ignition components, fuel pressure regulator, and injector seals...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Motor mounts and Injector seals took care of 80% of the rough idle the car had when I first got it, and a spark plug connector took out another 10%. The last 10% could be lots of different things I haven't bothered chasing down yet, as the mileage, performance, and acceleration are all within specs! I replaced the OVP with a new one, mostly to have a spare, but it didn't do anyrhing to the very slightly rough idle as far as I can tell. Hope this helps.

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

hey guys, I let my tech take a look at my car today. He says it's not the OVP relay but the injectors. He told me too add some fuel injetor cleaner and see what happens. He used some kinda adjustment tool and put it inside of the hole in the middle of the air filter cover. I gues that was to adjust the airflow. JCE what are injector sealers?

Those are the seals that go around the injector stem, sealing them to air intake manifold.

Vin

From your description, the problem you are having is not due to your OVP relay. The problem is somewhere else.