1992 300E 4matic revving at idle

superfret78 · 08-02-2009, 06:17 AM

As it says in the title, I'm having a problem with revving at idle. It will surge from about 750rpms to somewhere in between 1000-2000rpms and then drop back to normal. It does this about every 5-10 seconds or so....sometimes less. When I accelerate, it is sluggish sometimes. I just changed the spark plugs and they were grayish-white...so maybe the mixture is a bit lean. The car has been running a bit hot so I'm wondering...has that maybe damaged the crankshaft position sensor? Or maybe the IAC valve is sticking? Any suggestions? I'm about to replace the ignition wires as well because they don't look so hot.

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epowers777 · 08-02-2009, 06:45 AM

how many miles in engine? when was ur last tune up? Possibly leaky injectors? And if its running hot u check ur temp sensor I know that controls idle. Theres people smart than me on here I might be wrong!!

superfret78 · 08-02-2009, 02:46 PM

Thanks for the response. The engine has 247,000 miles on it. I'm not exactly sure on the last tune up b/c I bought it not long ago from someone. I don know that the engine was rebuilt about 50,000 miles ago. I also forgot to add that another detail with the idling problem is that sometimes the engine dies right after I put it in drive or reverse...or sometimes after driving a few yards it will cut out. Thanks for the thoughts!

epowers777 · 08-03-2009, 06:50 AM

ask here theres techs I can tell u ideas but not sure.
http://www.peachparts.com/shopforum/index.php
First pul lure idle control valve and spray it with carb cleaner and make sure u have no vaccum leaks and your cooling sensor might be bad Mine was a green top. Cooling sensor controls ur idle tells computer if its cold or hot

superfret78 · 08-03-2009, 05:31 PM

Yeah...the coolant temperature sensor is a possibility. I'm replacing it...may as well because its on an $18 part. I'll try pulling the IAC and taking a look at it. Thanks!

epowers777 · 08-03-2009, 05:36 PM

Make sure you replace the proper sensor one turns the fan and talks to the computer. One is just for the guage.

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08-02-2009, 06:45 AM	#2
epowers777 Senior Member Join Date: Apr 2008 Location: Forethill, Ca Northcal Posts: 395 Drives: 1986 300E Benz 1991 300te 4matic	how many miles in engine? when was ur last tune up? Possibly leaky injectors? And if its running hot u check ur temp sensor I know that controls idle. Theres people smart than me on here I might be wrong!!

08-02-2009, 02:46 PM	#3
superfret78 Newbie Join Date: Aug 2009 Posts: 3 Drives: 1992 300E 4matic	Thanks for the response. The engine has 247,000 miles on it. I'm not exactly sure on the last tune up b/c I bought it not long ago from someone. I don know that the engine was rebuilt about 50,000 miles ago. I also forgot to add that another detail with the idling problem is that sometimes the engine dies right after I put it in drive or reverse...or sometimes after driving a few yards it will cut out. Thanks for the thoughts!

08-03-2009, 06:50 AM	#4
epowers777 Senior Member Join Date: Apr 2008 Location: Forethill, Ca Northcal Posts: 395 Drives: 1986 300E Benz 1991 300te 4matic	ask here theres techs I can tell u ideas but not sure. http://www.peachparts.com/shopforum/index.php First pul lure idle control valve and spray it with carb cleaner and make sure u have no vaccum leaks and your cooling sensor might be bad Mine was a green top. Cooling sensor controls ur idle tells computer if its cold or hot

08-03-2009, 05:31 PM	#5
superfret78 Newbie Join Date: Aug 2009 Posts: 3 Drives: 1992 300E 4matic	Yeah...the coolant temperature sensor is a possibility. I'm replacing it...may as well because its on an $18 part. I'll try pulling the IAC and taking a look at it. Thanks!

08-03-2009, 05:36 PM	#6
epowers777 Senior Member Join Date: Apr 2008 Location: Forethill, Ca Northcal Posts: 395 Drives: 1986 300E Benz 1991 300te 4matic	Make sure you replace the proper sensor one turns the fan and talks to the computer. One is just for the guage.

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