Hi All, I have read a lot about the dreaded engine fault light and poor performance in the last week. My 1997 xk8 starts fine runs well and is lively. After about 15minutes when i back off the throttle the engine fault amber light comes on and goes off when i accelerate. It doesnt appear to trow a dcm code. If I drive for a while the red poor performance comes on and sometimes the car surges slightly. In this state I pulled codes P1226 once and P1227 once. A hard reset clears them. If I leave it for a few hours hey presto as if by magic all gone, then after 15 minutes or so of driving back it comes.

Throttle body or ECM? also at standstill i sometimes get stability control fail whilst i am not moving.

Thanks for any advice

kev

 

Start with checking the battery and alternator output. The battery should read in the 12.5v area or higher after sitting overnight. Even better if you can have it load tested. A lot of strange codes and warnings are the result of a weak battery.
If it checks out okay go through all the v+ and ground connections to be sure they are clean and tight.

 

OK got 12.35 volts and 14.35 with the motor running. Will go through +ve and ground connections next,..

 

I had a 97 for a bit. It has all the various fault codes come and go, would not run right, lost of power. various faults on ABS and other things. 97 was known for EMC issues so I sent mine out to be checked, rebuilt and when I put it in all the issues went away and 4 or so years down the line the current owner has had no issues.
Provided you have a good battery which I see can cause issue if it is about dead, and you start seeing all kinds of various fault codes that logically should not all start happening around the same time I would look hard at a ECU rebuild. I think this was an issue for 97 and 98 models???

 

P1226 & P1227 pertain to the Mechanical Guard which is used on the AJ26 Throttle Body. It's part of the Mechanical Connection between the Throttle Cable and the Throttle Body. The Cruise Control Vacuum Servo is Connected to part of it.