Hi,

My 00 XJR was throwing P0174 ’system too lean bank 1’ error code. Followed the advice on the forum and got the leak issue sorted and the code has finally vanished. Now when I start up the vehicle it has really rough idle, and code P0300 pops up. If I reset it the vehicle drives normal without any issues, but if I turn off the ignition then the same story starts again.

Should I be looking into replacing the coils and spark plugs? Looking for some guidance on what should be sequential order of the investigation be.

In Feb 2015 the dealer performed the fuel injection cleaning, carbon build up treatment. Could this be the fuel pump? What would be the signs for something more serious like a head gasket issue?

As always, I appreciate the guidance.

 

What is the status of your tensioners? Could be a timing issue.

 

Thanks for your response. When I acquired the vehicle I had the dealership do the big job on the timing chain, tensioners etc. Will the dealers scanner or a more comprehensive scanner be more specific on the cause?

 

Yes, the dealer-level scanner can provide greater accuracy. But I still suspect you have one or two issues: one, you have not caught the air leak in the intake system; two, the secondary tensioners may not have been done correctly.

Recheck the air intake system from the air filter to the throttle body, carefully. Clean the MAF sensor, and then clean the throttle bore and plate, carefully. Make sure sensor connections to the MAF are clean (use electronic cleaner); renew the plugs, look for oil in the plug wells; carefully reseat the coils (they may need to be cleaned as well).

You need to check fuel pressure, even though this should have been done when the injectors were cleaned. Still, might have dirty injectors (run a can of SeaFoam through a tank of high quality gas).

Since you are getting P0300, a random misfire as opposed to a specific cylinder, it is very hard to troubleshoot, requiring a shotgun approach. Maybe one of the forum pros will provide tighter guidance.

In the short run, you may be better served by having the dealer check it out.

Let us know what you find.