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Old 02-16-2004, 06:10 PM
Registered User
Join Date: Feb 2002
Posts: 45
Unhappy 300 E stalling out

I think the cause may be the ignition wires and plugs. Does this sound like a possible cause of a car that stalls out? The car will run fine during the day but it seems as if its running for a while or warm it stalls. What could be the cause. Do you think it may be the wires and plugs/ Thanks

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Old 02-16-2004, 08:21 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,538
Maybe the OVP?

There is a lot in the archives on this.

Try a search for "OVP" or "overvoltage protection relay".
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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Old 02-17-2004, 12:13 AM
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Join Date: Feb 2002
Posts: 45
Here's exactly what it does

When the car has not been run overnight, it runs fine in the morning until it reaches the ideal operating tempature. Once the engine heats up to the normal operating tempature, it will stall out as soon as you slow down under 25mph or come to a complete stop. I've been preventing it from stalling by putting it in neutral when approaching a stop or slow speed. Neutral raises the rpm's just high enough to keep it from stalling out. As soon as you put it in drive, it will stall out if you do not accelreate quick enough. The rpm's drop drastically when you are going slow and remove your foot completely off the gas pedal. Sometimes almost 90% of the time resulting in a stalled engine.

Here are my questions:

1. What else could be the cause... here are some of the things I've heard.
- Fuel Pump Relay

2. I bought new ignition wires and plugs and I'm going to install them tomorrow. Do you think this would make any difference in this situation?

3. It's so annoying because the car runs fine! Also, where is the fuel pump relay located on the 300E

Thanks a lot for any answers. I need to get this problem resolved by at least thursday.

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Old 02-17-2004, 11:50 PM
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Join Date: Apr 2001
Location: Joliet Illinois
Posts: 309
Stalling at Idle

This sounds like a classic case of a worn airflow sensor pot. The wiper inside the pot wears out at the normal idle position and the ECU loses input for a second causing a stall.

I had the same problem with my '88 260e. It would stall while idling or coasting to a stop. The pot is located on the front of the air flow sensor and has three wires going to it. It can be replaced but MBZ does not sell the pot separately. I purchased one through

Do a search on airflow sensor pot and there should be a lot more information on the subject.

There are many more causes of stalling and hesitation but if your car still has the original pot there is a good chance it is worn out.

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Old 02-18-2004, 09:31 AM
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Join Date: May 2002
Location: Mass
Posts: 1,127
Doubt it's the fuel pump or relay. When those go intermittant, they are not as predictible as you describe.
Also, inition wires and plugs are not likely culprits.

John's suggestions are likely on the right track.
1986 300E 5-Speed 240k mi.
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Old 02-18-2004, 11:01 AM
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Join Date: Feb 2002
Posts: 45
Thanks guys! Is this an expensive repair? I finally took it into an imports garage i know of around my area. The guy there seems to know his stuff. Do you think it's going to cost a lot to get fixed?
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Old 02-18-2004, 07:12 PM
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Join Date: Apr 2001
Location: Joliet Illinois
Posts: 309
Air Flow Sensor Pot

The airflow sensor pot I bought online was about $80 for an original Bosch. That's a lot for a simple little part but well worth it if it cures the stalling.

I installed it myself and it's not too difficult. The fuel pressure regulator needs to be disconnected to reach one of the screws and the new pot must be aligned correctly for the car to idle smooth.
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Old 02-20-2004, 04:12 PM
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Join Date: Sep 2003
Location: Kentucky
Posts: 19
It may be a vacuum leak in the vacinity of the idle air control valve. My 300TE would stall out after warming up as you came to a stop/slow turn. I heard a vacuum leak and finally found that the hose between the idle air control valve and the port under the fuel distributor had cracked on each end (after 200,000 miles ... what's the world coming to?). I put some seals all on the inside surface of the hose ends to get by until I can get a proper replacement. Runs fine now.

You might check this first before adjusting or replacing anything else.

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