Camry :: 2005 LE - Misfire When Idling And Trying To Accelerate Hard / P0304 Code

We recently bought a used 2005 Camry LE 4cyl 2.4L. When we test drove it there were hardly any symptoms and no CEL. After driving it for a week we start feeling a stuttering every once in a while, no CEL still so I thought it might just need a tune up.

Replaced the plugs (which were in bad shape, were Iridiums, friend mentioned it seemed like they were burnt, white blistering like high RPM burn) with new NGK Platinums and replaced the air filter (was also in bad shape, was K&N that was badly clogged up and black).

Drove it around, let it idle, turn on AC, no problem not a hiccup. Next day arrives and the car is misfiring worse than before. CEL comes on too. We get the codes and its the P0304 I mention in the title.

We check the coils and the plugs and they fire, we switch coil 4 and 1 and clear the CEL, then later the CEL comes back on and it's still P0304 so we rule out the coils. The plugs come pre-gapped also.

The misfires are at their worst when idling and trying to accelerate hard, I can hold it at 2000-3000 RPMs with no hiccups or very few ones. Misfires worse with AC on.

Only thing left to do is check compression, try to clean the injector with fuel additive and premium gasoline, or replace the injector, at least that's what I think.

It has 86000 miles.