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Hi, I've got a 2001 RAV4 with a 2.0L 1AZ-Fe engine.
Cyl 3 not firing at all speeds P0303 Error. Removing coil connector makes no difference in rpm all other cylinder drop rpm equally..
Have tried:
Swapping coils, spark plugs, remove plug attached coil and checked spark.
Swapping fuel injectors, check voltage to injector, matches others.
Checked for intake leaks.
Compression test, all cylinders around 150psi.
Removed top cover, check timing belt marks.
Replaced all 4 02 sensors. scanner says all the other sensor are working correctly Mass flow....etc....

Help !! I don't know what else to try.....

It sounds like you have eliminated nearly everything. But you could have a problem with the signal wire to either the injector or coil. I suggest that you take the vehicle to a good mechanic or auto-electrician - an oscilloscope test on the signal and feed wires, with the vehicle running, should normally pin-point the fault – if it’s related to these items.

If you haven't checked fuel pressure then I suggest you eliminate this as well before proceeding any further.