[ampegboy1]

Hi all,



Hope this is in the right place. I had an issue with the 968 tonight - the engine started bucking a bit when slowing down in traffic and trying hard to die when pulling away from a stop.



Whilst reading up on here and thinking back on the symptoms from a car park (how did we manage before smartphones?!), I realised that the dying was occurring when I came all the way off the throttle, e.g. rev the engine, release the throttle, the revs drop off and the engine dies instead of returning to idle, whereas if I held the throttle open somewhat it was ok. This behaviour was consistent and repeatable (and made manoeuvring in the petrol station on the way home 'interesting'!). From what I read, the most likely culprit would appear to be a faulty throttle position sensor. Since I bought the car in June the engine has, every now and then, 'bounced' up a few hundred revs after returning to idle and recently the idle immediately after switching on has sat at around 1,200rpm for a few seconds before settling at ≈850rpm (I had put this down to the cold weather). It appears to be fairly intermittent and the behaviour seems to me like a failing electrical/electronic component rather than a fuel/mechanical issue, especially since it runs alright otherwise. Any thoughts other than the <acronym title='throttle position sensor'>TPS</acronym>?



I'm planning to test the <acronym title='throttle position sensor'>TPS</acronym> at the weekend according to the info here and here, hopefully it will show up as faulty as then I'll have something that's obviously wrong! The info here says that it is adjustable - does anyone know a procedure for this, as it seems like the factory would have a quicker way than trial and error/feel. Is it just a case of move it, rev it, see if it dies and keep going until it's right? I don't want to replace it and end up with a new problem due to it being out of adjustment!



Thanks all,



Michael

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[ds968]

I would replace the DME relay ( or try cleaning the contacts of the relay first, and if that does not work replace it ). It's worth a $ 60 attempt, IMO. When one of my relays started to fail the engine was stumbling and had near-stalling symptoms when slowing down or lifting off the throttle.

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[ampegboy1]

Sorry Dan, the dangers of posting when tired - I must've cut the bit with the testing and forgotten to paste it back!



I swapped the DME relay with my spare but no change, and hunted round the engine bay for obvious loose/frayed connections but to no avail. The fuel was just past the last white mark on the gauge (56l on mine), but I don't think it was low enough to be sucking in dirt from the bottom of the tank.



Thanks,



Michael

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[fleetwood]

I'd check vacuum lines too -- I had one pop off once that caused similar engine behavior -- found it, put it back on, all was well

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[Cloud9...68]

I agree - sounds vacuum related to me.

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[fleetwood]

in my case -- it was the vacuum line under the fuel injector rail by the fuel pressure regulator

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[ampegboy1]

Thanks guys, I'll check those too.



Michael

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[polliviere]

Before spending any money I would remove and clean the idle control valve found under the throttle body. When this valve gets dirty or clogged your idle starts to hunt and you get throttle lift stalling.



Peter

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[DaveN]

Start poking around the ICV (Idle control valve) as well for electrical/vacuum problems. You can remove and clean it but it is a bit of a pain.

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[rl968]

Can the ICV be cleaned on our cars? I didn't think so, but could be wrong.



Does the car idle at all, such as when you start it?



I had similar issue, car would not idle, replaced ICV.

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[ampegboy1]

Thanks all, idle control valve added to the list <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />



rl968, apart from being high for a few seconds after starting she idles fine.



Michael

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[rxter]

+1 ICV

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[rl968]

[quote name='ampegboy1' timestamp='1386895474' post='153538']Thanks all, idle control valve added to the list <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />



rl968, apart from being high for a few seconds after starting she idles fine.



Michael[/quote]



I'd be leaning toward vacuum leak. A bad ICV means no idle and car will die, at least that was the case for me.

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[Cloud9...68]

Yeah, it seems like the idle control valve (along with the throttle position sensor) is often a suspect, but seldom seems to be the problem with issues like this. I bet it's a vacuum leak.

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[ampegboy1]

Hi all,



Just an update. I've not had a chance to spend any time looking for vacuum leaks so far, but I bought a Durametric in the meantime (I'd been looking for an excuse to get one anyway!) and checked for codes. I had a scare when it gave me a '41 - control unit faulty' error (which appears to refer to the ECU), but I think I've narrowed that one down to turning off the engine whilst the laptop is plugged in, as it went away when I cleared the codes and appears to be repeatable. Other than that one the fault memory seems to be staying clear, so the vacuum leak diagnosis is looking the most likely as, presumably, the <acronym title='throttle position sensor'>TPS</acronym> and ICV are ok if they aren't throwing up codes. Just to complicate things, I put her through 50 miles of town, country and motorway driving today and she ran beautifully!



Michael

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