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Matt
Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 21995
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Matt. 2002 S type 3.0 litre. Has developed a slight misfire under light throttle. I

Resolved Question:

Hello Matt. 2002 S type 3.0 litre. Has developed a slight misfire under light throttle. I can accelerate through it & starting is fine. Been going on for a couple of months & petrol has dropped a couple of MPG. Seems worse as it gets hot on a run. Idling fine & no lights up. Needs an ABS sensor, so this warning may be hiding another fault light? I may check one of the plugs I can get at. It had two ignition coil pencils & 6 plugs at 123k miles. Now 140k miles.
Thanks, ***** *****
Submitted: 1 year ago.
Category: Jaguar
Expert:  Matt replied 1 year ago.
hello if the ABS sensor is running / firing when it should not then its possible that the traction control is also being activated when it shouldn't this can create a ' misfire' type fault as power is cut by the ECU to cure wheelspin that isn't presentso I'd replace the faulty wheel speed sensor as the next stepand if thats Ok then this could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements. It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine
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