Tachometer needle moving in neutral

jimmurt

I've a 2008 Toyota Corolla with about 100k km on it.

In the last few months I noticed the tachometer needle moving back and forth between 1000 and 1400 whilst in neutral.

It just revs up to 1400 and then back down again.

At best, I'm worried that this is wasting petrol. At worst it could be a sign of a bigger problem.

Any ideas of what might be causing this?

corktina

fan cutting in? ditto aircon

kona

jimmurt wrote: »

I've a 2008 Toyota Corolla with about 100k km on it.

In the last few months I noticed the tachometer needle moving back and forth between 1000 and 1400 whilst in neutral.

It just revs up to 1400 and then back down again.

At best, I'm worried that this is wasting petrol. At worst it could be a sign of a bigger problem.

Any ideas of what might be causing this?

Can you hear the revs increase?

jimmurt

kona wrote: »

Can you hear the revs increase?

Yes, It's not just the needles moving, I can hear the revs increasing as the needle moves up and decrease as it goes done.

So the problem is not with the needle/tachometer, but with why exact is the car revving.

Iwannahurl

Does your Corolla have Variable Valve Timing (VVT)?

If so, my guess is that the changing RPM is due to the VVT.

b318isp

It's called hunting. It could be a vacuum leak on the inlet side of the engine or a problem with the system that controls the idle (such as an Idle Control Valve).

sogood

I don't know about your car specifically, but most cars have an Idle Control Valve. This would usually be a small cylindrical shaped device, with an electrical plug connected to it. It should be mounted, on or near the throttle assembly and they can become gummed up somewhat. Inside is a stepper motor/plunger and this is what can stick, causing erratic idle. IIt's as good a place to start as any. It' usually just held on with a few small screws and once removed, the plunger assembly can be cleaned with a carb cleaner/WD40 or similar.

ION08

Vacuum leak I'd say, check all rubber / plastic pipe / hoses in the engine bay

Cee-Jay-Cee

Iwannahurl wrote: »

Does your Corolla have Variable Valve Timing (VVT)?

If so, my guess is that the changing RPM is due to the VVT.

It is not the VVT. It's most likely a vacuum leak somewhere around the inlet manifold.

Does it do it all the time or just sometimes ?

jimmurt

Most of the time. I'm bringing it in for a full service and to get this repaired.

How much should I be looking at for both?

colm_mcm

They do this if you don't drive them enough/hard