Hi,the performance restriction light comes on at intervals whilst driving, i have changed the spark plugs and fitted a new upstream oxy sensor,please could you advise any solutions to this problem? many thanks, Howard

SOURCE: upstream oxy. sensor signal wire, what color is it?

In my 1990-1995 manual it is Black/Dark Green.

Dark green/orange is 12 V supply, Black is ground, Black/Light Blue also comes from the powertrain control module but is common to many other sensors.

SOURCE: restricted performance under load

I had the same problem on my 1998 XJ8. My dealer told me it was the Mass Airflow Meter, which needed replacing to the tune of around $500. After a second opinion at my local Jag mechanic, it turned out to be a hose that was broken on the lower part of the front of the engine. Check the vacuum hoses for breaks or loose fittings.

SOURCE: check engine light is on,display says restricted performance

Anything can cause the check engine light to go on from a loose gas cap, to a transmission issue. When the onboard computer detects an issue, it will restrict performance so as to not damage the engine any further. An Oil change won't affect this light. The only way to determine the cause of the light is to have the computer scanned with an OBD-II tool (Autozone does this for free) to determine the codes and cause for the light. You can also clear the light with the OBD-II tool, but if the problem is still there, the light will just come back on

SOURCE: When driving my X type 2.1 (2002) it jolts and

try ur air duct sensor

SOURCE: cylinder 8 misfire, restricted performance is also coming on

you may have to replace the cowl pack itself that sit on top of the spark plug and sometimes you can get by just changing the boot wish you the best of luck Michigan Man.