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W124 E300 12v 1992 and a 2009 Crown Victoria
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Discussion Starter #1 (Edited)
Dear All:

For a while now I've been having this issue where the engine sometimes revs weird on drive position.

The description is like; the engine revs a little lower than 500RPM and tries to balance that and jumps to above 500RPM a little and then again lower and keeps doing this until the engine turns off unless I accelerate. All this on the drive position in a full stop holding the breaks or moving slowly without using the accelerator, with the latter having the engine more prone to turn off dunno why.

All this with the A/C turned off and when I turn it on the condition gets some how more stable but with the problem still there.

Otherwise the car runs perfectly.

At idle the RPM waves in a very little margin that is not discoverable unless you're skeptical like me. No complaint here.

RPM is adjusted to 700RPM more or less and when the A/C is on, it goes down a little, like -50RPM or even less.

Any idea?

Thank you in advance.
 

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80 280SL, 85 300SD, 87 300TD, 90 300TE 4Matic, 90 300D 2.5 Turbo, 92 300D 2.5 Turbo, 92 300TE 4Mat
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1,469 Posts
Could be some carbon build up in the throttle body. Try a course of Sea Foam or something like that.
 

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W124 E300 12v 1992 and a 2009 Crown Victoria
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1,044 Posts
Discussion Starter #3
Thank you PWogaman.

I cleaned the throttle body with a spray that says carburetor and choke cleaner or something like that.

Is it the same thing? Or should it be a fuel additive? Could it be something between the fuel tank and the throttle body that makes this problem that requires the additive instead?
 

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"Gretchen" my 1986 300E 286000 km+ (RIP) August 2015
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1,092 Posts
Check your vacuum lines for leaks.
 

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E320/E250 Bluetec Ford F350 6.7l
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36,690 Posts
I am not familiar with this engine, but knowing that MB of this era have computerized idle control, I would suspect it takes a lot to have computer acting like that.
If you can't hook it up to good scanner, start with basics. New air filter, plugs if they are old, check the ignition wires and all engine sensors. Vacuum tubes usually don't create such strong symptoms, but good advise to check them as well.
 

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W124 E300 12v 1992 and a 2009 Crown Victoria
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1,044 Posts
Discussion Starter #6
GHM and Kajtek1, thank you for your support. All noted.

Just remembered that the problem came after replacing the idle control valve with a used one, but later on not right away, like in 3-4 days.
 

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1992 300D 2.5T (124.128) 1999 S320 SWB (140.032) 1999 E320 4Matic (210.082) 1984 300CD (123.153)
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177 Posts
Symptoms sound to me like a possible vacuum leak. Go through the engine compartment and look for any loose, disconnected or broken vacuum or air hoses, and replace as needed.

Running something through the fuel system would also not be a bad idea. Sea Foam is a great product, and Lubro Moly also makes a special fuel system cleaner for engines with CIS fuel injection. I think it is called Jectron.

Also, when was the last time you gave the car a proper tune up -- Plugs, wires, cap, rotor, air filter and fuel filter -- it may be time for those items to be replaced.
 
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