Any suggestions?
Normally it's 750RPM but today it's 950RPM.
It had a reasonable run of 120 miles a couple of days ago and fired up straight away this morning so I do not think it is the battery.
Any suggestions?
diesel? wanting a DPF cleanout run?
Telephone Preference Service, Tyre Pressure Sensor...?
Battery a bit low, so it's running at a fast tick over to generate a bit more current?
Throttle Position Sensor. Perhaps not returning to its default position.
I'd be looking for an air leak into the plenum. Likely a split hose, etc. Allowing in enough extra air to put it outside the range of the idle control valve.
Assuming a petrol car. Diesels are a black art to me.
Do modern computerised cars have such a thing?
Little screw on the carburettor or fuel injector that you twiddle with an appropriate tool?
Yes.
But these days a three track potentometer at the go pedal. Three tracks I think are main and spare and a reverse law check. You really don't want a good old "noisy pot" as your engine throttle control...
Is that once warmed through or just after starting from cold? Maybe it's still running with a bit of choke after a cold start.
after warming up? It may think its still cold,. like bad water temp sensor
How long did you run the car today?
Have you left the Air Con on? On some cars it's automatically turned on when directing the airflow to the windscreen (it pre-dries the air).
It's diesel.
Ah - you deserve what you get, then. ;-)
I had a 1993 VW Golf (petrol) and occasionally the engine would die just as I'd started moving when pulling out of a junction. I got used to hitting the hazard light switch and swerving towards the kerb if it felt it happen! The car was in the garage loads of times and they could never reproduce it so they could never fix it. I clocked up a lot of garage labour in investigating it. Eventually, after it had happened once too often and I'd narrowly escaped being rear-ended, I told the garage "keep it for as long as you need and loan me a car until you've fixed it". Several days later, the garage man rang me in a state of excitement. They'd finally identified the cause: a worn/cracked/dirty throttle potentiometer costing a few pence - but the labour would be several hundred pounds because the car was out of warranty. Luckily I keep all my garage bills and the first one described the problem and noted the mileage. It was about 500 miles within the manufacturer's mileage limit for the warranty so all subsequent investigation work was covered because it hadn't been fixed while it was still under warranty. Apparently VW head office and the VW dealer argued the toss as to who should pay, but the important thing was that *I* didn't have to pay - and got back the money I'd already paid for the abortive investigations.
I had similar thoughts, also: Faulty reversing switch Faulty clutch switch
Have you got an ODB2 debugging dongle you can plug into the car? That will tell you if there are any fault codes.
Can't see that with an alternator.
Could perhaps cold damp air having a higher oxygen content, be getting it more excited?
Or, some winter program in the engine management trying to coax some viscosity out of the oil?
Alternatively, I had a Lagnua that applied a bit more throttle when idling, that was when the air con was active.
Anyway, some management system should be ultimately governing the speed safely. There are a few interesting vids on youtube on what happens if ye let a diesel do what it naturally wants to do, without that control.
I wanted LED and rear wheel drive.
It was after it was warmed up. But a nice run up the M1 at 70MPH[1] seems to have fixed it.
[1] it was 70MPH as she was driving.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.