I purchased a pristine 04 in December 12 (64K miles, one owner), but it had a #4 cylinder misfire to be fixed before purchase. Sequentially changed plug, HV wire, coil and finally entire head before finally (supposedly) correcting the problem. Now 7 months and 5K miles later the problem is back (code 0304). Nobody can verify that the above mentioned parts were the ONLY parts changed, but my guess at this point is that #4 injector (or some foreign particle) is at fault. Anybody have other thoughts?

Rod

 

Never guess with a Rover or you will go broke buying parts not needed or called for by any fault codes.
How mechanical are you, can you follow directions, if so get back to me with your number and I'll call and walk you thru what to do.

 

They changed the head at their expense? That was significant.

Injector, wiring to same, and wirng to knock sensor or knock sensor mounting might also be issues. Injectors get plus battery volts all at the same time, and the ECU grounds them individually to squirt. Injectors have a spec for resitance, so you can check them with a meter, just compare several with the suspect one. Could be a skinned wire touching. Shake the harness. Also, go out tionight in the total dark and look under hood at idle for any arcing around coils, wires, boots.