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Richard, Jaguar Technician
Category: Jaguar
Satisfied Customers: 15392
Experience:  12 years at a Ford/Lincoln Mercury and Jaguar dealer as technician and shop foreman.
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99 jaguar xk8: it going into fail safe mode/reduce performance/ etc

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99 jaguar xk8, I've had problems with it going into fail safe mode/reduce performance/ etc. I have taken it to the shop countless time and always I get a bill for nothing. Apparently the art of trouble shooting has gone with the invent of the computer. However the throttle body was replaced, but like every other time it seems fine for a couple of weeks then the same faults. At one time the car wouldn't start, it would crank over but seemed like it was almost locking up. I had it haul to a local master mechanic and he said he had to soak it with break fluid to get the compression back up. I had him change the plugs and service the transmission. He told me I just needed to drive the car more (I would if it wouldn't leave on the side of the road). Since then I drove every day for about 2 weeks then the same problem. So today I took the air intake cover off just to check the air filter and look for loose electrical connectors on the throttle body. I notice that with the air intake cover off and the mass air sensor unplugged the car was missing at 2800 RPM. If the mass air sensor unplugged does not cause this miss, other than a bad plug, plug wire, what should I look for that will cause the engine to miss? Also can you tell me where to get a maintenace manual for this vehicle looks like I'm going to need one.

v/r, Ron

Hello and welcome to


So right know the vehicle no longer has a starting problem but does have a missfire when driving? Did the restricted performance warning message come back on?

Customer: replied 6 years ago.

That is correct, it starts fine, and it's misses at exactly 2800 RPM both driving or in park. The restricted performance, with check engine light red or yellow is illuminated, depends on the mood of the car.


Ok you may have a problem with an ignition coil. Pinpointing which one will be difficult but since the engine light is on this may help. Since that warning came on there should be fault codes stored that the dealer should have been able to read with their scan tool. You can use an OBD II scan tool to retrieve the faults as well. Most parts stores like autozone or pepboys usually do this at no charge. See if you can get a four digit code from the system which may give us an idea of the problem.
Customer: replied 6 years ago.
Pinpointing which one, so each plug has it's own ignition coil and is that something I can replace in my garage? If this is the problem is it possible to pinpoint by removing individual plug wires and listen for a difference in the engine? I will try to make it to a autozone and get back to you with the code information.
Yes each spark plug has it's own coil. They can be replaced very easily. You can remove each one to see if there is a change in engine rpm but before doing that lets get the fault codes. We do not want to induce any codes just yet.
Customer: replied 6 years ago.
Okay I'm back from auto zone, they were able to pull the codes but did not have jaguar info. Here is what they pulled: P0111, P0112, P1229, P0102, P1111. One other issue is that I get a low coolant message, but the coolant reservoir is full.
The fault codes P0111, P0112 and P0102 were induced when you removed the mass air flow sensor. The code P1229 is for the throttle motor. This is usually either a faulty throttle motor or relay. Since you stated you had the throttle replaced this may be covered under a parts warranty if done at the dealer. You could have all those fault codes cleared then scan it again once the warnings come back on.
Customer: replied 6 years ago.

Does either the throttle motor or relay or disconnecting the mass air flow sensor have anything to do with the miss at 2800 RPM?

Not really but since the mass air flow sensor was disconnected it may have fouled the fueling adaptations. Clear all the fault codes and disconnect the negative battery terminal cable for 10 minutes which reset the fuel adaptions.

Customer: replied 6 years ago.
How do I clear the fault codes?
Go back to autozone and have them clear the fault codes.
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