997 idle hunting issue - not solved through diagnostics!
Discussion
Hello all - I have trawled through the forums here and found some issues closely related to the one I am having, but nothing which matches perfectly.
So...
The engine idle on my 2004 997.1 Carrera is doing some bizarre things: it sometimes sits at the usual c.1000rpm idle, but frequently dips to 3-500 as you slow to a stop, before jerking back up to c.1000rpm. Sometimes it sits at c.700 and idles roughly / feels like it’s about to stall. It has the check engine error light on permanently.
I have taken it to a specialist (not OEM) who replaced cam shaft sensor, plugs and coils on one bank based on the diagnostic showing misfire issues. After all of that the problem is not resolved (and yes given they gave it back to me suggesting it was resolved I am pretty furious with the specialist!)
Any ideas? Could this be MAF? If so wouldn’t the diagnostic just show a MAF issue? The most confusing part for me is that the diagnostic is showing misfires but (i) the main misfire fixes have not seemed to work and (ii) it just doesn’t ‘feel’ like a misfire issue - it’s an idling issue.
Go easy on me if I am being thick / this is covered elsewhere on the forums - it’s my first time posting and I have looked through a number of other threads to try and find the answer, I promise!
Thank you all
So...
The engine idle on my 2004 997.1 Carrera is doing some bizarre things: it sometimes sits at the usual c.1000rpm idle, but frequently dips to 3-500 as you slow to a stop, before jerking back up to c.1000rpm. Sometimes it sits at c.700 and idles roughly / feels like it’s about to stall. It has the check engine error light on permanently.
I have taken it to a specialist (not OEM) who replaced cam shaft sensor, plugs and coils on one bank based on the diagnostic showing misfire issues. After all of that the problem is not resolved (and yes given they gave it back to me suggesting it was resolved I am pretty furious with the specialist!)
Any ideas? Could this be MAF? If so wouldn’t the diagnostic just show a MAF issue? The most confusing part for me is that the diagnostic is showing misfires but (i) the main misfire fixes have not seemed to work and (ii) it just doesn’t ‘feel’ like a misfire issue - it’s an idling issue.
Go easy on me if I am being thick / this is covered elsewhere on the forums - it’s my first time posting and I have looked through a number of other threads to try and find the answer, I promise!
Thank you all
Start the car from cold; let it idle, does it sound OK?
If it is tappet related, generally from a cold start they sound fine and run smoothly - with the characteristic crackling from the exhaust....
After 120-200 seconds it should come off warm up; timing will shift with variocam and the tappets will switch to low lift (from a cold start they are set to high lift with late ignition timing to heat the cats quicker).
If a misfire is evident at the shift to low lift its likely the tappets are sticking - especially given the basics have been done - swapping the lift solenoid bank to bank (the misfires will switch to the other bank if its the solenoid) can be a quick check but, if the misfires stay on the originally affected bank again, tappets would likely be the cause.
If it is tappet related, generally from a cold start they sound fine and run smoothly - with the characteristic crackling from the exhaust....
After 120-200 seconds it should come off warm up; timing will shift with variocam and the tappets will switch to low lift (from a cold start they are set to high lift with late ignition timing to heat the cats quicker).
If a misfire is evident at the shift to low lift its likely the tappets are sticking - especially given the basics have been done - swapping the lift solenoid bank to bank (the misfires will switch to the other bank if its the solenoid) can be a quick check but, if the misfires stay on the originally affected bank again, tappets would likely be the cause.
Thanks Pope (and everyone else!)
It's as you describe - the idle is fine until the car drops off the warmup, when it hunts (i.e drops to 300prm, then jumps back to 900, back to 300, etc).
Perhaps I have misunderstood but when it idles like this it doesn't seem like a 'misfire' per se - i.e. you can't hear a cylinder missing in the tone of the engine note - it's just the revs dropping to almost stall levels, and then jumping back up.
Is that what you meant? If so it does indeed sound like the tappets...
It's as you describe - the idle is fine until the car drops off the warmup, when it hunts (i.e drops to 300prm, then jumps back to 900, back to 300, etc).
Perhaps I have misunderstood but when it idles like this it doesn't seem like a 'misfire' per se - i.e. you can't hear a cylinder missing in the tone of the engine note - it's just the revs dropping to almost stall levels, and then jumping back up.
Is that what you meant? If so it does indeed sound like the tappets...
Hugo-15802 said:
Thanks Pope (and everyone else!)
It's as you describe - the idle is fine until the car drops off the warmup, when it hunts (i.e drops to 300prm, then jumps back to 900, back to 300, etc).
Perhaps I have misunderstood but when it idles like this it doesn't seem like a 'misfire' per se - i.e. you can't hear a cylinder missing in the tone of the engine note - it's just the revs dropping to almost stall levels, and then jumping back up.
Is that what you meant? If so it does indeed sound like the tappets...
When the tappets stick it's not an electrical misfire - the intake valves are still opening to 11mm (high lift), whereas the fuelling is for the lower 3mm lift setting; the result is a weak mixture misfire. It's as you describe - the idle is fine until the car drops off the warmup, when it hunts (i.e drops to 300prm, then jumps back to 900, back to 300, etc).
Perhaps I have misunderstood but when it idles like this it doesn't seem like a 'misfire' per se - i.e. you can't hear a cylinder missing in the tone of the engine note - it's just the revs dropping to almost stall levels, and then jumping back up.
Is that what you meant? If so it does indeed sound like the tappets...
The Variocam adjusters can stick - resulting in erratic or plain incorrect valve timing.
It does sound like your symptoms - but some more diagnosis would pin it down. The valve lift Drive Link using the PIWIS tester can be used to check the switching function, as can the Variocam test which runs the variator sprockets though their actual range of motion against expected setpoints.
Various cases have been resolved in different ways; I have seen an engine flush and 2 or 3 consecutive hot oil changes cure both problems but particularly obstinate ones have had to have the tappets or Variocam adjusters replaced.
Edited by Pope on Monday 4th January 23:10
My 997 is sat for weeks sometimes at this time of year without a run, is it better to sit there with the trickle charge on or would it be better to sit ticking over for 15 minutes a couple of times a week? Also when first started after 4 weeks there seems to be a lot of white smoke/fumes, is this likely to be condensation/moisture or something else? Thanks.... stay safe. 
spice92 said:
This might sound overly simple, but is the oil cap on properly? (Or is there an air leak that means the engine won't hold it's internal vacuum? Check aos hoses etc)
Good shout - My oil filler neck developed a tear - caused some issues. All fixed now, but the difference was astonishing 
If you intend to leave a car in storage/unused over the winter, I understand the considered thinking is not to start it up & not drive it - it apparently doesn’t do it any favours as it creates unnecessary moisture in the exhaust and the engine only sits at idle speed etc. & it is much better to just leave it untouched on a battery conditioner until it gets a proper run of say 30 minutes plus at varying road speeds. There a plenty of guides on how to prepare a car for long term storage including over inflating the tyres to stop flat spots or using a wheel saver/cradle/cushion arrangement.
MrC986 said:
If you intend to leave a car in storage/unused over the winter, I understand the considered thinking is not to start it up & not drive it - it apparently doesn’t do it any favours as it creates unnecessary moisture in the exhaust and the engine only sits at idle speed etc. & it is much better to just leave it untouched on a battery conditioner until it gets a proper run of say 30 minutes plus at varying road speeds. There a plenty of guides on how to prepare a car for long term storage including over inflating the tyres to stop flat spots or using a wheel saver/cradle/cushion arrangement.
Cheers. 
This might also sound overly simple, but how often do you use it, and for how long a journey?
If there are no nasty metallic noises, an Italian tune-up would be my first diagnostic, though you may struggle with that if by some one in a million chance you were pulled over.
Well officer, some voice on the internet told me to go out for a long drive.....
If there are no nasty metallic noises, an Italian tune-up would be my first diagnostic, though you may struggle with that if by some one in a million chance you were pulled over.
Well officer, some voice on the internet told me to go out for a long drive.....
Orangecurry said:
This might also sound overly simple, but how often do you use it, and for how long a journey?
If there are no nasty metallic noises, an Italian tune-up would be my first diagnostic, though you may struggle with that if by some one in a million chance you were pulled over.
Well officer, some voice on the internet told me to go out for a long drive.....
This time of year, maybe once a fortnight & probably 30 miles ish of driving. Drives & sounds great. Just a lot of smoke after being sat for a couple of weeks. This was today.If there are no nasty metallic noises, an Italian tune-up would be my first diagnostic, though you may struggle with that if by some one in a million chance you were pulled over.
Well officer, some voice on the internet told me to go out for a long drive.....
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