I've been getting the same issue on our 1998 XK8 for months. Performance is not degraded, but the message is annoying. Hadn't though of the MAF (I'll try that). Symptoms were the restricted performance light would come on when the car was hot, usually after hitting a rough bit in the road. I'm guessing it is the accelerator pedal (APP) sensor. By shooting a bit of electrical contact cleaner in the connection for the vacuum line on top of the APP, the problem would be gone for a few drives. Don't think the car is overheating, at least no obvious symptoms. Now that the weather is cooler, it isn't happened. Sadly, no longer have a big garage space and the extensive tools that once were there.... (sigh). However, the local Jag club has suggested a shop that knows these cars and as soon as it's time to take the car off the road, it'll go for a visit.

 

Buy a new mass flow sensor. Got a new one and it solved similar problems. Old one did not send codes . Best money I spent...

 

I've got the engine light on permanently, when I drive the car it's fine up to about 50 or 60 m.p.h. then restricted performance comes on which lasts between fifteen seconds and two or three minutes, then it turns itself off and is fine for the rest of the journey. No drop in performance that I can notice. I've changed the MAF, the o2 sense, fuel filter and throttle body. The only reading I get is P0171, running lean. Any ideas what could be causing this? Thanks.

 

Replace the MAF sensor connector!

 

Check fuel trims - lots of threads to read