1992 300E 4matic revving at idle
08-02-2009, 05:17 AM
#1
Newbie
Thread Starter
Join Date: Aug 2009
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
1992 300E 4matic
1992 300E 4matic revving at idle
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. 
08-02-2009, 05:45 AM
#2
Senior Member
Join Date: Apr 2008
Location: Forethill, Ca Northcal
Posts: 405
Likes: 0
Received 0 Likes
on
0 Posts
85 euro w124 300d non turbo black on black......coming soon hx35 turbo intercooler
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, 01:46 PM
#3
Newbie
Thread Starter
Join Date: Aug 2009
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
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, 05:50 AM
#4
Senior Member
Join Date: Apr 2008
Location: Forethill, Ca Northcal
Posts: 405
Likes: 0
Received 0 Likes
on
0 Posts
85 euro w124 300d non turbo black on black......coming soon hx35 turbo intercooler
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
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, 04:31 PM
#5
Newbie
Thread Starter
Join Date: Aug 2009
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
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, 04:36 PM
#6
Senior Member
Join Date: Apr 2008
Location: Forethill, Ca Northcal
Posts: 405
Likes: 0
Received 0 Likes
on
0 Posts
85 euro w124 300d non turbo black on black......coming soon hx35 turbo intercooler
Make sure you replace the proper sensor one turns the fan and talks to the computer. One is just for the guage.
07-21-2013, 08:11 PM
#7
Newbie
Join Date: Jul 2013
Location: Southern California
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
1992 300E 3.0L
I know this thread has been dead for some time but I figured I'd share my experience with this issue.
Had exactly the same issue as described, the problem ended up being the throttle position switch.
Without this switch working right, the car does not know if you're resting at idle or not which ultimately seems to confuse it pretty bad.
I attached a photo and the part # i found for it was this:
0025456814
Switch; Thrust Cut-Off Micro-Switch at Throttle Linkage on Intake Manifold with Single Roller/Lever
By quickly looking at the throttle assembly, it's clearly visible. Most likely will have to remove the air filter to get a good look at it.
Had exactly the same issue as described, the problem ended up being the throttle position switch.
Without this switch working right, the car does not know if you're resting at idle or not which ultimately seems to confuse it pretty bad.
I attached a photo and the part # i found for it was this:
0025456814
Switch; Thrust Cut-Off Micro-Switch at Throttle Linkage on Intake Manifold with Single Roller/Lever
By quickly looking at the throttle assembly, it's clearly visible. Most likely will have to remove the air filter to get a good look at it.
Last edited by Benzer08; 07-21-2013 at 08:16 PM. Reason: Additional info added
