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2009 Toyota Yaris 148,000 miles

On my mother's name I swear my first fill up, this little monstar gave me 70 mpg. Now barely 20mpg.

.....

Sparkplugs new and looking good. No wetness, nor electric burns.

New coils function properly and looking good.

Compression proper and consistent across all four.

Not losing coolant. Not losing oil. So there are zero signs of head gasket failure.

MAF sensor and throttle house clean.

Dealership said fuel injector 1 was switched with 2 and the problem followed from cylinder #1 to #2 (this move was already checked and for me the code didn't follow the switch, nevertheless...) and so they did not move the fuel injectors back to place of origin and assured me that replacing the #2 fuel injector  would suffice.

However,  once I pulled in to my mechanic's parking lot (within the hour of dealership diagnosis), curious, I ran a scan before handing over the key and it still read P0301. My mechanic replaced both injectors #1 and #2 for good measure.

Negative terminal removed for 2 hours to reset the computer.

I picked the car up after hours, and the problem persisted and threw code P0301 STILL!!!

Besides screaming F it and rigging up some C4 between the manifold and the firewall, what would any of y'all suggest?

PLEASE HELP (*****),

C.