Engine idle speed - revs on its own, is it timing belt?

Vazelothir · 07-05-2009 11:42AM #1

Hi,

hoping someone could give me a steer on what might be wrong with my engine.

When the engine is on but in neutral it seems to rev up on its own and ticks over faster than normal. It generally only happens after the car has well warmed up (i.e. it doesn't happen all the time).

Could it be the timing belt ? or could it be something else?

Timing belt probably does need to be changed, but I just have a nagging feeling that it is not the cause and there might be something else wrong...

I had a hole in the air intake hose until recently, and I was hoping that was the problem (it isn't!)

Any thoughts?

thanks

alias no.9 · 07-05-2009 11:44AM

How much do the revs increase by? It could just be something like a gummed up throttle.

dohc · 07-05-2009 11:46AM

MAF sensor could need cleaning
Throttlebody could need cleaning too!

cantdecide · 07-05-2009 11:50AM

Could be anything.

I had a 325i that hunted like crazy and it was the lambda sensor. Is it heavy on fuel lately?

Anan1 · 07-05-2009 11:54AM

It's not the timing belt anyway, they're either working perfectly or broken. Are you sure it's not just the a/c compressor kicking in and out?

Voodoomelon · 07-05-2009 11:58AM

That's what I thought. The engine speed will also alter according to the load on the alternator.

Webmonkey · 07-05-2009 11:58AM

If the timing belt skipped a tooth, you'd have problems more to do with miss firing, low power etc.

It probably the IACV acting up. Might need a bit of cleaning.

HashSlinging · 07-05-2009 12:11PM

Is it a petrol or diesel, having the exact same issue with my 2.0 TDi and I've had the throttle body cleaned, looking at fuel sensor and MAF next.

Fun times.

_Kaiser_ · 07-05-2009 12:17PM

HashSlinging wrote: »

Is it a petrol or diesel, having the exact same issue with my 2.0 TDi and I've had the throttle body cleaned, looking at fuel sensor and MAF next.

Fun times.

That's what it was on my old 02 TDI Passat - same symptoms as yours and the OPs

L-M · 07-05-2009 12:24PM

+1 on the aircon bit!

HashSlinging · 07-05-2009 12:50PM

Kaiser2000 wrote: »

That's what it was on my old 02 TDI Passat - same symptoms as yours and the OPs

Did you replace the MAF yourself?

If it was a simple enough thing to do I'd do it myself.

also anyone know if a pierburg maf will fit the 2.0Tdi.

Whispered · 07-05-2009 12:55PM

Could be the throttle body. Had the same thing happen. Be careful, it will get worse and before you know it you're sitting at traffic lights in a little 1.1l car revving like a boy racer sap

.

Seriously though, do be careful, when it was happening on mine the car tended to run away as soon as you lifted the clutch, like you had your accelerator to the floor. Dangerous when you're in traffic.

Webmonkey · 07-05-2009 12:56PM

helena.ryan wrote: »

Could be the throttle body. Had the same thing happen. Be careful, it will get worse and before you know it you're sitting at traffic lights in a little 1.1l car revving like a boy racer sap .

Seriously though, do be careful, when it was happening on mine the car tended to run away as soon as you lifted the clutch, like you had your accelerator to the floor. Dangerous when you're in traffic.

Modern cars ECUs should put the car into limp home mode if these problems arise. But I wouldn't depend on this!

Tefral · 07-05-2009 12:59PM

Worth checking the Vaccum hoses around the car as even if there is a small slit this can cause what your describing.
Listen out for a hissing noise. Generally though these complaints are breathing related so i wouldnt worry about a slipped timing belt really

AlienGav · 07-05-2009 01:08PM

What make and model is the car?

There's usually a slow idle valve on most modern petrol cars, you'll find it in and around the air intake, could be that or the mass air flow meter. It's a common fault on some petrol Fords... :pac:

L-M · 07-05-2009 01:10PM

This may be of no help, but when my Golf was doing the same thing, it was this pipe that was off.

mickdw · 07-05-2009 01:17PM

Cracked hose somewhere, possibly after the MAF sensor on the intake or dirty throttle body would be most likely but it could be a number of things

Vazelothir · 07-05-2009 01:19PM

its a 2000 1.4 petrol Astra, when in idle it often ticks over around 1500-2000 rpm instead of around 1000-1100... like a boy racer sap ;-)

when its not ticking over at 1500 it jumps on its own, far as I can tell its not anything kicking in...

will check the hoses, I've a feeling that there might still be a leak...

listermint · 07-05-2009 01:37PM

If you were at the intake recently then more than likely that was it. Slightest slit or if the ends are not put back on in the right direction ( alot have notches , could be upside down) this prevents a proper seal.

Although i had similar issue in my E46 and it turned out to be camshaft sensor. Oil was affecting the reading. took it out and cleaned Presto

Vazelothir · 07-05-2009 02:34PM

thanks folks, appreciate the help.

stifz · 07-05-2009 04:28PM

same thing happened on mine. its was a worn throttle spring. 2mins to fit and about a euro to buy.

nice.

Engine idle speed - revs on its own, is it timing belt?

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