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Old 10-19-2002, 09:22 AM
Posts: n/a
300e high idle all the time

I'm getting no where real fast and spending money. so far I have replaced the idle valve no help, I also replaced the fuel pressure regulator because gas was coming out of what appears to be the atmosphric vent (a line coming off the front of the regulator and going into the hose from the air cleaner to the top of the valve cover. the gas flow stopped with the new regulator. There are three temp sensors on the drivers side of the head, the middle one is for the instrument panel temp gage. I have ohmed the sensors both hot and cold, all readings are with the meter set on the 20K scale, first sensor cold reads 4.07 ohms hot .61 ohms the third sensor cold reads 3.60 cold and .69 hot (cold ambient temp was 73 degrees F (approx 22 deg C) hot temp readings from car temp gage approx 27.5 deg C. Are these readings normal? I can unplug the connector from the idle valve and RPM drops about 500. Also the radio antenna when turn the radio on starts up then goes right back down, after that the antenna will not do anything. Does that indicate the mast assembly is bad? There is an item mounted on the drivers side in front of the antenna, what is it and what is its purpose. Does anyone know if there is a description of operation located on the Mercedes Service manual disc for the fuel injection and where is it?
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Old 10-21-2002, 02:27 AM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
What year is your 300E? Your throttle linkage may need to be adjusted, or your deceleration shutoff microswitch replaced, among other things.

I would check these first. When your engine is idling high, press the little roller wheel in on the microswitch. Your throttle linkage makes contact with it and tells the engine to reduce fuel inj. If the idle decreases when you test it, then you can try to bend the little roller arm so it pushes farther in, or just replace it. Dealer list cost is $23.

Other things to check:

air flow sensor position indicator
throttle valve switch

Good luck

'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

Last edited by pmizell; 10-21-2002 at 02:34 AM.
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Old 10-21-2002, 03:59 PM
Live to Learn
Join Date: Mar 2002
Location: Raleigh NC
Posts: 145
Dont rule out vacuum leaks.
Mercedes Benz Master Tech
ASE Master Technician
Diagnostic Technician
Owner of "Behind the Star Inc."
Raleigh NC.
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