View Full Version : Intermittent Idle problem Audi A3 1.6
A3 puzzler
19-05-2009, 11:00 AM
My Audi A3 1.6 (1999) has an intermittent idle problem. When it plays up, the revs hunt from between 1000-1300rpm and this can be felt as a surging when driving slowly or gearing down. When I feel the cable pulley at the throttle body I can feel it pulling at the throttle cable up and down like a boy racer at the lights.
The diagnostics computer has not reported any faults except for a throttle sensor fault which no longer shows.
So far, I have replaced the throttle body, replaced the timing belt, taken it in for a full service, done a default reset and each time, the problem has gone away only to return weeks later.
There is no correlation with the temperature of the engine but what I have noticed is that if it is OK and then switched off for over 10minutes before being restarted, the problem comes back. The engine runs with a good even power output over the rev range and is otherwise perfect.
Another clue is that if I rev the engine up to 5000rpm for a couple of seconds, the engine will settle down, and rev evenly at a very steady 800rpm for anything between 10 minutes and a day.
Could this be the Mass airflow sensor...any ideas please?
Look for an air leak, sounds like unmetered air is getting to the
engine.
Look for split pipes or tiny holes.
A3 puzzler
21-05-2009, 02:19 PM
Thanks for the suggestion, I will take another look - I have just replaced pipes handling air to the throttle body and everything else that looks a bit 'past it'.
Do you really think that this is consistent with a fault that can present itself hot or cold stay for days and then disappear for days? I would expect an intermittent air leak to occur either at a particular temperature ( as parts expand) or with mechanical disturbance. I have tried rocking components around to see if it makes any difference ( it does not) and as I have said, the fault can occur hot or cold.
What do you think of my other suspects: idle stabiliser, temperature sensor, O2 sensor, Ground to the ECU- or other ECU fault that would not show up on diagnostic computer?
It could be the MAF, but how long are you going to throw parts at it !!
A3 puzzler
22-05-2009, 09:45 AM
I don't know how much longer I am going to try to sort this out. I have a 41 year old Austin that is quite capable of ticking over reliably without a hint of a computer!
I really like this Audi but the whole experience is ruined by this problem ...and it does not even show up on the diagnostics computer.
I was hoping that someone with some expertise would be able to diagnose from the information that I have given the most likely cause...I do not have much practical experience, I just understand some of the principles.
...So, if the MAF is faulty could that cause the revs to rise and fall as described?
What does the fact that I can feel this rise and fall of revs even when I am gearing down mean?...is the idle management designed to carry on working in the background all the time or is there a switch?
Frustratingly, I have not been able to find anyone with a sufficiently analytical mind to be able to work this out for me.
Just seen your in London.
Try sending a PM to adamss24, he's a member on and I think he has a garage...
A3 puzzler
26-05-2009, 05:53 PM
Thanks...I got my A3 scanned again this weekend and this time instead of no faults it came up with too many! The MAF, the temperature sensor,the throttle body ( I think it was the idle stabilisation)...they all came up. I have got the faults cleared as I do not believe it can be all of these things at the same time and plan to drive around for a few days before getting it scanned again to see if just one fault comes up. - I am going to presume that the one that comes up is the culprit.
Crasher
26-05-2009, 06:00 PM
You have done the right thing having it cleared and trying it again after a few days driving. Ohh and about the Austin, I agree with what you say but the Audi could probably run on the unburnt hydrocarbons coming out of the Austin’s tailpipe.
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