Vectra Uneven running

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Wed 26 Feb 2003 21:04
Vectra Uneven running - superannuated rocker
Can anyone please help me with a problem with an elderly Vectra. The car is a 96P 2.0SRi. The problem is uneven running at small throttle openings or on the over run when the vehicle is warm. The car idles perfectly well and runs quite smoothly from cold and when warm runs fine given a reasonably large amount of throttle. The problem feels like a hesitation and lumpiness as though there is uneveness in fuel supply or an intermittent inlet manifold leak. Reading my Vectra and fuel injection manuals, I suspect either the fuel tank breather system (FSCV) or Exhaust Gas Recirc (EGR)systems both of which apparently only operate when the engine is warm. Last weekend I disconnected the FSCV solenoid with no effect. I assumed the solenoid was energise to open, however, I am not sure whether it may be the other way round. Can someone please advise. Also I would like to render the EGR valve inoperable to see if it is the culprit. I understand is vacuum operated. can someone tell me which sense it operates in and whether I can disable it by pulling off one of the vacuum hoses. Alternatively am I barking up the wrong tree altogether and is there a well known Vectra fault with the symptoms I have described? My car also occasionally exhibits the Vectra cutting out syndrome at idle but this is quite infrequent and typically happens every six months or so.
Any Ideas gratefully received - many thanks
Superannuated Rocker
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Wed 26 Feb 2003 21:18
Vectra Uneven running - Andrew Moorey (Tune-Up)
Unfortunately, if you disable the EGR valve the ECU will know and throw the system into LOS and put the MIL light up. Sounds like either the O2 sensor could be lazy or the throttle position sensor on its way out. The problem is that these awful engines suffer with many problems it is difficult to know what to suggest. I think the best bet would be to get the fault codes extracted by your local GM dealer or a reliable independent. Faults with the tank vent system are rare and EGR problems tend to be more drastic and will usually trigger the MIL light as will the other problems such as Cam and Crankshaft sensors and parasitic voltage spikes from the alternator etc.
Andrew



Happiness is a T70 at full chat!
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Thu 27 Feb 2003 00:14
Vectra Uneven running - superannuated rocker
Thanks very much for the reply. I\'ve tended to discount the throttle position sensor as the problem does not exist when the engine is cold. I know the mixture will presumably be richer then which may mask the problem but there is no obvious point on the throttle position where the difficulty occurs. Also the problem is obvious on a closed throttle on the over run yet the engine idles ok with the same throttle position. The only fault codes I have are from the weekend when I disconnected the CFSV solenoid. I note your point about the O2 sensor but at present it is not illuminating the MIL light. I wonder if my plugs suggest a weak mixture, I\'ll look at the weekend.
Thank You again
SR
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