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Old 12-16-2003, 04:36 AM
Gunawan's Avatar
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Join Date: Sep 2002
Location: Jakarta, Indonesia
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Unhappy Sudden surge when decelerating.

Anybody could give me a hint on why my car ,300E' 88 with manual transmision, having a sudden throttle surge when decelerating with the pedal brake pushed lightly and without stepping on the clutch. This happens all the times at about 2000 rpm to 1500 rpm. For information, I have a new OVP installed and working Microswitch (I checked) on the car.
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Old 12-16-2003, 11:02 PM
Gunawan's Avatar
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Join Date: Sep 2002
Location: Jakarta, Indonesia
Posts: 23
Guys, come on, no replies?
The problem is annoying because the sudden rpm surge happened for a fraction of a second caused the differential gear thumped and in the long run will ruin the propeller shaft rubber joint.
Thank you in advance.
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Old 12-17-2003, 12:02 AM
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Join Date: Apr 2002
Posts: 257
It may be the airflow meter potentiometer. Do a search on that, there's a lot of info on it in this forum.
1985 190E 2.3-16 Euro
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Old 12-17-2003, 05:25 AM
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Join Date: Sep 2002
Location: Jakarta, Indonesia
Posts: 23
thank you for u're kind reply. I do that. Found some threads on this air flow sensor potentiometer. Is it the short stem beside the air flow plate assy? Because I couldn't find anything with picture attached about this potentiometer.
tnx before hand.
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Old 12-17-2003, 08:52 AM
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Location: Near Raleigh, NC
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Here it is.
Attached Thumbnails
Sudden surge when decelerating.-amf1.jpeg  
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified
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Old 12-17-2003, 01:16 PM
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
To add, unplug the connector from the pot to see if the symptom disappears. Other driveability issues might occur then, but it's a useful test.

'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7
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Old 12-17-2003, 02:58 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Does it happen just as you tough the brake, or does it happen at a fixed rpm as you decelerate? If when you touch the brake, you probably have a leaking brake booster.

If not, it's something with the fuel injection -- verify that the EHA current is correct and not ocsillating -- if it goes way negative (fuel cutoff) then bounces rather than going back to near zero, check the duty cycle and verify correct mixture, and check O2 sensor function. You could have a slow O2 sensor causing mixture flucuation on deceleration.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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