Idling problem on 2004 fabia 1.4 16v

[justatic]

Hi there,

I've a 2004 Skoda Fabia 16v 100BHP.

I've an idling problem which has developed in the last few weeks and wondered if anyone out there has encontered a similar problem.

It only occurs when the engine has warmed up and the revs have settled down to 750-800rpm and the engine is idling. When driving normally there is no issue whatsoever but when I come to a halt and let the engine idle at first it seems normal then within 10-15 seconds the idling will become very unstable and I assume at this point the engine management takes control and increases the rpm to 1250 or so to avoid the engine cutting out. I have to turn off the ignition to reset this 'safe' mode.

I've had a look for blocked, oily or split rubber hoses around the intake and have found no evidence of any. The car has been recently serviced but the fault persists. Just thought I'd pose the question before I head back to the VAG Tech.

[Rob.]

This is a common fault on that engine..

Do a search and have a read.. what you'll find is that some people haven't found the cause, but with 90% of them it's an iffy coolant sensor and/or dirty throttle body.

It sounds like yours maybe doing what my last Fabia took to doing (around this time of year too).. over fuelling because it thinks it's very cold and ups the fuel in the mixture.

You may find it becomes hard to start in the future.. but of course, I could be well off the mark as well.

[justatic]

Many thanks for your replay. I have read about the possibility of a faulty coolant sensor previously. Your suggestion does make good sense though, it does seem as if the mixture is causing the problem. I plan to try the coolant sensor tonight. Could you possibly tell me the location of the coolant sensor and/or part number to check before buying.

thanks again

[Rob.]

Sorry bud.. Got it done at a garage.. all I know is that you can get to the sensor from above on the right hand side....

Do you know anyone with Vagcom? You can see what the sensor is outputting through it.. if it's duf (as mine was).. the read out will be all over the place.. up, down, down some more, back up, up higher.. etc etc ..

If it comes back stable it may not be the sensour.

[ap0gee1978]

I don't know where the sensor is on the 1.4 16v, but the part number is 06A919501A. I did a guide here, which should help, even if the exact position of the sensor isn't on it.

Before trying that, though, see if it settles down with the air con on. I don't know why, but both of our cars (1.4 8v and 1.9 PD130) are a bit rough at idle if it's off. Both cars have new-ish CTSs and no recent fault codes, by the way...

[justatic]

If a coolant sensor is at fault, I assume the temperature reading on the dashboard will give incorrect readings. Mine seems to give a true reading even when the fault occurs.

[Rob.]

Not the case I'm afraid, Mine was always fine. Think the dash temp gauge is oil temp, faulty sensor in question is coolant so doesn't show in dash.. (I think, not sure, but that's what I believe anyway)

[ap0gee1978]

The gauge on the dash shows COOLANT temperature. Disconnect it if you don't believe me!

However, I have seen an incipient CTS fault that has presented as a faulty gauge, and I have seen one that had no effect whatsoever beyond a rogue CEL. It depends on the failure mode of the sensor, and also whether it trips 'limp mode'. Basically, the gauge on the dash is very, very approximate (which is why when everything's working OK, it will rise smartly to straight-up-and-down and stay fixed there no matter how fast you drive and how hard you push the engine. However, if it's giving spurious readings that aren't too far off the mark, then it may be enough to cause the ECU to do funny things even though the gauge is working OK...

[Rob.]

That's what mine did... when it wouldn't start I'd get the EPC.. but after a few drives and non-problematic starts it'd clear..

My needle never moved, but going by what the VAG-COM said, the fluctuations were very sporadic. Perhaps yours (the OP) is behaving the same way?

[justatic]

I've taken your initial advice and removed and cleaned the throttle body with carb. cleaner. The condition has improved greatly. The idling is much steadier-with no fault condition showing on the dash (as yet). A slight hunting on idle is still apparent every now and again (maybe 50-100rpm). One thing I have noticed is that on initial start up the revs seem momentarily high then settle down to normal levels (without the accelerator being touched). Is this a sign that the throttle body needs calibrating? Can I reset the ECU's saved values and allow it to 're-learn' by disconnecting from battery?

Many thanks from a much happier Skoda driver!

[Rob.]

Think that's normal tbh mate