Engine Revving on it's own

[EvianBaby]

When I was sitting in traffic last night I noticed my engine appeared to be revving of it's own accord. Only up to 1,000 rpm every ten seconds or so.

Is that normal?

[factor-fiction]

No it's not normal. I had that last year- I think it was something to do with the clutch but it was covered by the warranty so I didn't take too much notice of the reasons

[AlBags]

^ That is if the clutch is slipping while you are driving.

This is a different issue.
Hunting up and down every now and then? What car and engine?

[EvianBaby]

It's a 53 plate 1.6 Golf.

[factor-fiction]

Sorry, yes- my engine would suddenly rev while I was driving, often in slow moving traffic.

[EvianBaby]

Oh, no mine doesn't do that. I was stationary at the time.

[AlBags]

New clutch yet, F?

[EvianBaby]

Sorry Al, do you mean have I had a new clutch fitted? If so, never since I've owned it (about 7 years)

[AlBags]

OK .. Golf.
Few things according to engine fitted will affect engine idle.
None are serious .. rather annoying. One or two can later cause engine stalling of it's own accord.

Idle control valve can get clogged and requires washing out.
Disconnect and reconnect the small pipe from the inlet manifold to the oil breather (before the butterfly) and see if idle stabilizes.
Brake servo pipe (from inlet manifold to servo) check for leakages (common on 1.6) That will effect idle.
Clean out carboned-up throttle body with carb cleaner. (open throttle wide and spray liberally/wipe out with paper)
You can do all of these pretty easily and cheaply. Need a can of carb cleaner!

[AlBags]

Yes Ev ... so are you just 'putting up' with the slipping clutch then, for now?

[AlBags]

Sorry .. I meant Factor with the clutch slipping!

[EvianBaby]

Sorry to be dumb but what do you mean by the clutch slipping?

[EvianBaby]

Oooohhh ok.

What you describe is not something I could do. Would it be an expensive job for a garage to do? I've already spent a fortune on my car this year :(

[AlBags]

Something a car DIY er could do ..
A garage would charge about an hour I suppose.
I did it various times while doing other servicing jobs on a car. You could wait for a service and ask that the throttle body and valve are cleaned out .. specifically.
You could also look at the servo pipe, I suppose!

[sunny-dave]

Just a thought - could it be the engine cooling fan cutting in/out - quite normal as a car sits in traffic?

I've known cars which react to the extra electrical load from the fan by just upping the tickover a bit until the fan cuts out again.

[AlBags]

The ecu does that anyway .. just like raising idle RPM by about 50rpm when air con is switched on.

[sunny-dave]

So could that be what EB is noticing?

[DTCwordfan]

I had it with a sticking air intake valve on a Saab 9000 turbo many years ago - took them forever to find the problem as the engine diagnostics were pretty basic back then.

[EvianBaby]

Uh Oh, I'm seeing lots of words that mean nothing to me.

I did wonder about the fan so I kept checking the thermo and it just remained in the same place the whole time. It wasn't over heating.

I popped out a short while ago and noticed it doing it again while I was waiting at a junction. I could see in a reflection the headlights also seemed to dip a little bit when it was doing it.

[AlBags]

SD ... Ticking over at lights even in hot weather, you would only be likely to hear fan cut in (or out) once ... and not likely at all in this parky weather.

[AlBags]

(especially when temp gauge sits on normal)

DT's prob with Saab was the same valve. It's an idle speed control valve on those, same as BMW used to use.
I advise you to stick with the list : )