i just replaced all the hoses, thermostat and housing in my '08 XJ8. I took it for a twenty minute test drive, no problems, the next day, I went for another test drive, after about a mile, she started sputtering and the check engine and restricted performance light came on. The codes I got are P0300, 301, 302 & 304.

Is this a weird coincidence, and another problem just started, or should I look at my work and see if I missed something?

 

Most are 2-trip codes which is why it was your 2nd drive when they flagged.

It does tend to be the most recent work that's worth suspecting.

 

I haven't done any other work except the hoses and thermostat.

 

Found some write-up about these codes in JagRepair.com:
http://www.jagrepair.com/images/Auto...to%20P0308.pdf
So these codes means multiple cylinder misfiring, and misfiring specific to Cylinders #1, #2 and #4; enough clues for a more detailed investigation.

 

Did you spill any coolant on the wiring or ignition coils?

 

When the hose busted, it sprayed coolant everywhere, under the hood. That was the second hose to break on me in a year, so I decided to replace them all

 

I would spray and clean out all the wiring and connectors with electronics cleaner first. Cheap and easy might do the trick.

 

Thank you!