LH 2.4 can be a finicky system to diagnose since it's adaptive and the ECU doesn't get ALL of the data it needs for a diagnosis (like fuel pressure at the at the fuel rail). The injector failure code is common when there is a serious mixture problem. However, the injectors are likely fine.

Sounds like you're running rich, so a vacuum leak is likely not the immediate culprit.

Replacing the FPR is probably a good idea since (even if it's not the problem) it's cheap is probably ready for replacement in the next few years, and it's a pain in the arse when it goes.

Have you reset the computer by removing the main LH fuse (or disconnecting the battery) for a couple minutes? Have you done the classic AMM test? Disconnect the AMM (with the car off!). If the car runs better, you likely have a bad AMM.

Good luck!
-Ryan

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Athens, Ohio
1990 245 DL 130k M47, E-codes
1991 745 GL 280k (Girlfriend-mobile)
Buckeye Volvo Club