My jag is having "random misfires" when warming up. i get a restricted performance for a bit then it goes away. i checked all the plugs. they are all good. i replaced them 20k ago. both valve covers had the plug oil seals replaced 5k miles ago when i did the tensioner update.

any one have any idea were to look next?

 

Might consider cleaning the MAFS, TB and part load breather. All easy and certainly due on a 10 year old car.

 

I can tell you I had a random misfires and it was the coolant temperature sensor. I was luck to fine it because the pipe was leaking. I order a new one and the sensor came with it. After changing the pipe the misfires was gone. You can try this unplug that senor when the car is cold and you will see the car runs like crap. And the pipe with the sensor was about $40.00. This is only a FYI.

 

Testpoint, MAFS, TB and part load breather have already been cleaned. Thank you for the suggestion.

Two jags, I will check that in a little white with my scanner and see if the sensor output matches the other sensors.

Thanks

P.S for clarification, it only happens when its starting from dead cold.