Engine revving itself up

[AndyT77]

Every now and again when i approach a junction and slow to a stop, my engine revs will rise, sometimes upto about 3k rpm.

It doesn't happen all the time, but when it does the only way to stop it seems to be to depress the clutch, put it in gear, and then reverse the operation.

The car is a 2004 1.8 Ford Focus. Any ideas?

[Jayfish]

Check for loose trim above the pedal, I had this issue once.
Other than that I'll defer to the more knowledgeable out there.

[Codswallop]

I had a similar problem on my old 1999 Focus 1.8 petrol. Common cause of the problem on that engine is often a sticking idle control valve, and the solution is to take off the valve and give is a good clean. The valve is relatively easy to get to (being on top of the engine), so it may be a good first port of call.

[AndyT77]

Codswallop said:

I had a similar problem on my old 1999 Focus 1.8 petrol. Common cause of the problem on that engine is often a sticking idle control valve, and the solution is to take off the valve and give is a good clean. The valve is relatively easy to get to (being on top of the engine), so it may be a good first port of call.

Hmm, doesn't sound too difficult to do. Any info on it's precise location/what it looks like and how to clean it?

[VeeTEC]

It'll look something like this

http://www.google.co.uk/imgres?imgurl=http://www.w...

Soak the mechanical parts of it in carb cleaner.

You should find it somewhere on/around the intake manifold.

[Dangerous Dan]

Probably not the issue with this particular car....

I had a Megane with a 1.6 engine that developed a fault in which the engine would start accelerating/revving when I was at "idle". This eventually lead to the car stalling and would not start for a short period (flooding).

Transpired it was a faulty coolant temperature sensor registering a -something-or-other temperature and telling the ECU to "add more fuel, capt'n", believing the engine was cold and needed a richer (??) mixture to warm up.

Temp sensor swap out followed by a precautionary ECU flash sorted this problem out. Sensor was circa £20-£30 iirc?

[okie592]

defo idle speed control valve,happened to both my focus'

[AndyT77]

Dangerous Dan said:

Probably not the issue with this particular car....

I had a Megane with a 1.6 engine that developed a fault in which the engine would start accelerating/revving when I was at "idle". This eventually lead to the car stalling and would not start for a short period (flooding).

Transpired it was a faulty coolant temperature sensor registering a -something-or-other temperature and telling the ECU to "add more fuel, capt'n", believing the engine was cold and needed a richer (??) mixture to warm up.

Temp sensor swap out followed by a precautionary ECU flash sorted this problem out. Sensor was circa £20-£30 iirc?

Hmm, on my recent service they recommended i have a new temp sensor fitted, so this makes sense. Also, the temp guage never works, so it always looks like the engine is cold.

[Shoukie]

I had this recently, there's a vacuum hose that comes off the air inlet pipe and where it connects to the back of the engine I'd knocked it off when I'd re-fitted the engine cover. It over revved when I was stopped, in neutral or with the clutch down so maybe not the same with yours, but the hose could just be loose.

[AndyT77]

Thanks for all the replies people, certainly have a few things to look at.

[Dangerous Dan]

AndyT77 said:

Hmm, on my recent service they recommended i have a new temp sensor fitted, so this makes sense. Also, the temp guage never works, so it always looks like the engine is cold.

No experience with Fords, but on Renaults the sensors seem to be very fragile and require replacing. Same with the "pencil coil" coil packs (Circa £30 each, 4 required as 4 pot engine).

Then again, my car was, obviously, French. Therefore, electrics aren't its strong point.

The temp gauge never working? That could be a wiring fault to the dashboard itself I would assume? If the ECU thought the engine was actually cold, it would be dumping fuel into the engine like crazy (basically, my problem, albeit maybe different causes). If it runs OK but the temp gauge is fecked, that tells me a wiring fault between sensor and dashboard dial, but otherwise functioning OK?

TBH, I am not a mechanic. I know more about programming SQL servers and upkeeping Exchange servers than cars. They go broom-broom and cost a lot, right? (kinda like women!)

[shoehorn]

Cylinder head temp sensor between plugs 2%3.