throttle blipping at tick over

[gaml d4d]

Hi everybody,

My 1.4 petrol 2008 Auris (Not hybrid) has for me a strange fault.

Car has done 108k miles

At tick over (hot or cold) the engine will not sit at constant revs.

The revs bounce from 1500 and then immediately back to 1000 revs and then again immediately to 1500rpm.

I checked the MAF and it looks clean

Air filter is reasonabley new and looks ok

I put in new plugs but this did not help.

Cant find any holes or damage in any of the rubber tubes or around the air filter.

The car runs fine when driving, power is OK and exhaust fumes are not black or smokey 

This fault has started very suddenly and nothing obvious changed previously

 

Any Thoughts?

[Bernard Foy]

Dirty fuel or moisture in your fuel??

[gaml d4d]

I thought about fuel, but think it is unlikely. Car is used daily and still has half a tank of fuel and was filled up over a week ago. It also runs beautifully with plenty of power and no misfire

[Mooly]

Could it be an issue with either the throttle positioning actuator (I'm assuming its drive by wire and not a throttle cable) or throttle pedal encoder (if drive by wire).

You could always try resetting the ECU (Battery disconnect) and letting it relearn the correct idle point although if there is a definite fault that will fix it. It might be worth doing for elimination purposes though.

 

[gaml d4d]

Its not drive by wire - old fashioned cable. But i will try resetting the ecu, thanks

[gaml d4d]

I've disconnected and reconnected the Battery and that made no difference.

Any other ideas?

[Mooly]

Not really tbh. The fact you say it suddenly happened does suggest a failure somewhere although resetting the ECU I think had to be done as trouble shooting step.

How is the idle speed controlled... I would guess by the crankshaft sensor and by comparing the output of that (frequency) to an inbuilt reference within the ECU. So no easy things I can think of, I suspect you are into some real time diagnostics to see what is going on. 

Could a dirty throttle plate do this? I really don't know. I would think that might be more random though.

[TonyHSD]

If it’s old fashioned throttle body likely to have icv idle control valve and if it’s faulty it will do exactly the same as the op has experience, fluctuating idling. Another reason could be a vacuum leak, sometimes difficult to find. 

[gaml d4d]

Many thanks to Tony.

Problem was the throttle control valve. It didn't look that dirty, but luckily I have a little steam cleaner and an old toothbrush. took the air intake tube off and 2 minutes steaming and rubbing and the metal was all shiny again. Car now ticks over smooth as ever ☺️☺️

[Mooly]

Excellent, I'm pleased you have sorted it.

[TonyHSD]

Great, 

I am glad it’s all sorted now. 👌