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Thread: Unknown Engine Fault

  1. #1
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    Unknown Engine Fault

    Before the Christmas holiday break, having just washed my 2007 4.2 litre XK, I took it for a quick blast up the road to dry it off and spin-dry the wheels. About 2 miles from home I swept it round a roundabout in a U-turn and floored the throttle in order to roar away with an impressive squeal of tyres and a bark of V8 exhaust.

    And the engine cut. Well, it didn't cut, but suddenly it wouldn't rev. No warning lights, but the car wouldn't go more than about 20 mph. Luckily I was just a couple of miles from home, so I limped back with my hazard lights on, continually waving other vehicles past. Very humiliating.

    I didn't have any time to investigate - I was going away for Christmas - so I simply connected my CTEK (of course!), locked the car, put its cover back over over it and left it.

    I've now had a chance to re-examine it. The engine started and there were no warning lights, but rather alarmingly (with my foot completely off the throttle) the revs kept surging repeatedly between 500 and 1100 rpm, at a frequency of approximately 20 times a minute.

    My little iCarsoft i930 scanner showed the following DTC codes:

    P0101 Mass or volume air flow - circuit range / performance mass or volume air flow/range / performance problem
    P0507 idle air control system RPM higher than expected
    P0441 Evaporative emission system incorrect purge flow
    P016A Internal control module toque performance

    (No, I don't know what these mean either!)

    When the engine appeared to have warmed up I switched it off, left it a few minutes and re-started it. The rev-surging had stopped, it ticked over at a normal steady speed but the iCarsoft showed the same fault codes.

    I didn't risk trying to drive it (I didn't want to break down and be stranded!), but I shall try tomorrow and if it's driveable I presume the smart thing to do might be to take it to my local indie, about 5 miles away, and seek their advice.

    I suspect some engine / air flow sensor is playing up or stopped working or has become disconnected, but I also cringe at the feared sound of a cash-register's 'Ker-Ching!' somewhere in the distance!

    Has anyone had a similar problem or know what the likely cause (and cure!) is, please?
    Jaguar 2007 4.2 litre XK (X150) convertible
    Maxzda 2007 MX-5 2.0 litre (non - 'Sport') roadster-coupe
    Skoda 2007 Octavia 2.0TDI 4WD (not a Scout) estate
    Reliant 1975 Scimitar GTE SE5a (off the road after 243,000 from new)

  2. #2
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    Could a clue be in the fact that you had just washed the car when this happened? Water in any air intakes? Long shot but it is a very unusual problem.
    2 rejected F Paces for a 2018 XF 2.0D AWD Sportbrake. caesium blue with goodies. 2006 4.2 XK Convertible Frost Blue & Ivory for wonderful summer use.

  3. #3
    Senior Member simpo3's Avatar
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    An exhibition-quality piece of straw-clutching Mr Jaws Let's hope you're right, and next time he dries the wheels with a cloth...

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  5. #4
    Senior Member MarkyM's Avatar
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    It takes some real effort for water to enter the air intake or electricals, even with a 180bar pressure washer with the bonnet closed.

    My bit of straw clutching would be some some of the plastic bits leading to or from the air sensor, and AFM (if it has one) have become brittle with age....and the car is 12yrs old.

    Water under the bonnet should be pretty easy to see in daylight.

    Hope it all works out Titus....keep us posted.
    2014 XK Dynamic R Coupe (no backbox, supercharger pulley upgrade and K&N's)
    Audi A6/C6 quattro - going soon
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    Peugeot 2008 EAT6 with pan roof and heated seats - new addition

  6. #5
    Junior Member Myron's Avatar
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    Sounds like the car went into "limp home" mode for some reason. My prediction is that your mechanic will determine the cause is unrelated to the immediately-preceding wash...

    I hope you find the cause quickly and relatively painlessly!

  7. #6
    Senior Member Beefbeefbeef's Avatar
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    As you say, the symptoms sound as though there is a problem with the engine not reading the amount of air coming flowing in.
    I've had problems with air flow in two previous Jags, one was sorted by replacing the air flow sensor and the other was a "sticky" butterfly valve on the air intake which needed to be cleaned - both relatively inexpensive.

    Would be interested to hear the conclusion to your story.
    2009 XK 5.0 Portfolio

  8. #7
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    Quote Originally Posted by Myron View Post
    Sounds like the car went into "limp home" mode for some reason. My prediction is that your mechanic will determine the cause is unrelated to the immediately-preceding wash...

    I hope you find the cause quickly and relatively painlessly!
    Thanks! I had heard of 'limp home' mode but never experienced it - if that's what it was. Slightly surprised that I don't recall any warning lights showing. I doubt that the car-washing had anything to do with it. No pressure washer used, just my usual routine: a gentle sprinkle with a garden hose to loosen the grime, a wash down with a bucket of warm water and car shampoo using a wash-mitt, then another sprinkle to rinse off, and finally a quick wipe down with an absorbent towel.

    I'd be interested to hear the views of an experienced member like 8bit.

    And yes, if/when I get the problem sorted I will of course report back. (I actually favour the death penalty for posters who report a problem but then never report back with the eventual outcome. Grrr.)
    Jaguar 2007 4.2 litre XK (X150) convertible
    Maxzda 2007 MX-5 2.0 litre (non - 'Sport') roadster-coupe
    Skoda 2007 Octavia 2.0TDI 4WD (not a Scout) estate
    Reliant 1975 Scimitar GTE SE5a (off the road after 243,000 from new)

  9. #8
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    The fact that it happened when you floored it makes me wonder whether an air hose or electrical connector has popped off. The oscillating idle when cold may point to an air bleed somewhere.
    Current Jag: 2010 5.0 XKR (XKR-S X-Pipe, smaller S/C pulley and Tune ~650bhp - 11.567@123.19, max v=126.04!)

    Previous Jags: 2007 4.2 XKR | 2004 4.2 XJ8 | 1998 4.0 XJR | 1996 6.0 XJ12 | 1989 5.3 XJ-S | 1983 5.3 XJ-S | 1980 5.3 XJ-S

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  11. #9
    Senior Member 8bit's Avatar
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    Quote Originally Posted by Titus View Post
    When the engine appeared to have warmed up I switched it off, left it a few minutes and re-started it. The rev-surging had stopped, it ticked over at a normal steady speed but the iCarsoft showed the same fault codes.
    May be a fault in the SAI system, if the problem appears to go away once the engine is warmed up.
    Current: 2009 XKR 5.0
    Previous: 2008 XKR 4.2

    I take photos of cars! Find me on Facebook, Instagram and Flickr.

  12. #10
    Senior Member Peterv's Avatar
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    Quote Originally Posted by Titus View Post
    When the engine appeared to have warmed up I switched it off, left it a few minutes and re-started it. The rev-surging had stopped, it ticked over at a normal steady speed but the iCarsoft showed the same fault codes.
    Did you erase the codes the first time you connected the Icarsoft?
    There is no substitute for cubic inches!

    Jaguar XK 4.2 2006

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