W124 300TE fast/high idle issue

[J-Scho]

I have a 1990 W124 300TE which has developed an idle speed issue over the last few days. When I start it from cold it idles at around 1500rpm instead of the usual 800-900rpm. I put this down to the weather going colder and it having to use choke but even once the engine is warm, it still idles at 1500 if I put it into neutral.

This morning I was stuck in traffic and could tell it wasn't right by the fact it was moving away quicker as I released the brakes and sure enough, I knocked it into neutral a couple of times and it would rise right up to 1500rpm. Them, I decided to turn it off and start it up again. Straight away it idled perfectly at 800-900rpm as usual.

Does anyone have any ideas please?

 

[J-Scho]

Same thing happened this morning - stuck in the same traffic, and if I put it into neutral it would rise up to 1500rpm. Switched off and restarted and it idled normally at 800rpm.

 

[jaymanek]

The idle valve sticks on this engine. However first thing is to check if your OVP relay has ever been changed.
These cause issues like this and are pretty much a consumable to replace every few years.

Over Voltage Protection Relay... About £50 from the dealer.

 

[Ermir]

Idle control valve

 

[J-Scho]

Thank you for your help guys.

Can the idle valve be cleaned out with carb cleaner or similar?

Also, where are the idle valve and OVP relay please?

 

[Ermir]

I think it can. But dont use screwdriver as u can damahe the iner coat. Just spray on and dru with a paper or towel