W124 - 300TE idle speed

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Kenny124

New Member
Joined
Dec 5, 2018
Messages
19
Location
Falkirk
Car
W124 TE300
I recently changed the alternator on my 300TE (M103 engine). Now my idle speed when the engine is warm varies between 750 and 1200 rpm. It sits steady but the idle speed is different every time!

Before the alternator change it sat at a steady 650 rpm (when warm) all the time.

Can anyone explain and advise how I can remedy this? I've already checked the cable and it is not sticky.

Thanks in advance!
 
Kenny Should be up in the 800s close to 900 check the vacuum hoses all over the engine for splits .And on the earth points on the engine to chassis ,remove the bolt clean up the area umder the earth cable apply a little grease, and bolt back up . Remove battery clamps and clean up the - + poles on the battery apply grease and then lock them back up, - but dont do this if you have no radio code ! . Did you fit the same part number alternator Its a strange one this .
 
Thanks for that.
Yes, the same alternator and also a new belt. A winding broke on the original unit so replacement was the only economic option.
I'm wondering if I have disturbed a vacuum pipe when working on the front end? I've had a quick look but can't see anything astray.
I'll go out this afternoon (I'm in Scotland and it is just 1.5 degrees here this morning) and will also check the battery and earth connections as I did have the battery disconnected.
I'm not too worried about it but want to return to a normal regular idle speed!
 
Kenny pull the plug on the alternator and try it without it in the system .Dont run it long without the alternator off but only do this to proove if it is the alternator or not
 
Kenny check the fuse on the top of your Over Voltage Protection relay at the back of the battery you will see a black shield ,,it sits behind it.It will be the only one with fuses on .
 
As you did not mention the ABS light being on , i suspect that it's not the OVP. Check for vacuum leaks as you may have bumped a vacuum line.
 
Problem solved. It turns out it was the rubber covering on the throttle pedal - it has split at the bottom and was catching on the floor mat. When the car was off the road for a few days waiting for the new alternator I had the mats out to clean them and I forgot about this - I must have disturbed the rubber cover when I put the mat back.
I've now removed the damaged pedal rubber cover and the idle is now perfect again. Simple solution!
Many thanks for all the suggestions and advice.
 

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