Restricted Performance

[lncandr]

I have a 2000 XJ8 and recently the CHECK ENGINE and RESTRICTED PERFORMANCE warning lights have appeared on the dash.The engine is very lumpy and uneven on tickover and it won't rev above 3000 rpm.I read somewhere that it could be an ignition coil failure but I would be most grateful for any further advice from more knowledgeable people than myself.

[J44EAG]

Wasn`t there a recall on the throttle body on the XJ8? Main Dealers would fix the problem FOC as it was a safety issue. I believe the engine would just cut out.

Coils that are defective will cause misfires as will worn plugs that if allowed to continue to misfire, will eventually damage the coils. Duff coils can cause the management light to illuminate and the car to run as fail safe.

The throttle actuation is by accelerator cable rather than fly by wire as on S-type, X350 etc.
At least you can rule out a duff accelerator potentiometer. The feed back pot on the throttle can break down as indeed car the TAC module .(Throttle Actuator Control)

Best advice would be to have the car scanned to save time, money and guess work. Some form of fail safe or limp home scenario seems to have occurred.

Perhaps someone else here could add a few pearls of wisdom.

Mike

[SV8Predator]

Nothing to do with the throttle body I'm afraid, and they don't get replaced FOC any more, so don't get your hopes up!

And no pearls of wisdom either, as no one here has the slightest idea of what the problem could be.

The only way to proceed is to put a code reader on and see if any fault codes are present.

As the car has gone into 'restricted performance' mode, this is normally caused by an emissions-related fault. Thus an ordinary OBD II / EOBD fault reader should suffice (as opposed to the OEM device which reads a different part of the ECU.)

As an example, the code reader may show a P0354 (ignition coil 'D' - primary / secondary circuit). Now as this is an emissions-affecting fault, it will put the car into 'restricted performance' mode (to protect the cat). It may be an intermittent fault and the car may return to normal a few minutes (or seconds) later. But will probably get worse over time and as the engine warms up.

So put a new coil unit onto cylinder 'D' and you should be back to normal. A bad connection at this coil would throw up the same fault code.

But these are just examples. No one can advise any further until you get a fault code. And that will point you in the direction to follow for your subsequent fault finding.

[Evna]

I had spate of the restricted performance message which I believed was due to a problem with Cruise Control as it only seemed to occur when I was using it or it was switched on... took it and had it checked on two occasions for fault codes... none present!! continued on for another month and I also noticed that when the cruise wasn't switched on I occasionally got the Bulb fail warning... checked bulbs and rear light units all working fine. Decided to change the Brake light switch but it continue to throw up a bulb warning or restricted performance message (when cruise was switched on) every couple of days... so I finally changed both brake light bulbs... and in the last 4 months there has been no recurrance... assumption probable faulty bulb... causing technology to go t*ts up!!