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Hello. Do you know which cylinder is misfiring?
P0174 is a bank 2 lean code. P0301 is a misfire in cylinder 1 which is in bank 1, so they shouldn't be related. I assume that the injector and coil that you had replaced were both on cylinder 1? Have you tried a compression test to make sure that the misfire isn't the result of poor compression in that cylinder?
You changed the injector in cylinder 1?
did the condition get worse after replacing the intake gaskets?
Ok. You cleared codes I assume, and the cylinder 1 misfire was all that returned?
the fact that it idles better indicates that you probably had a vacuum leak which was probably repaired when you replaced the intake gaskets
Ok, then you have a code on it's way very shortly. I am sure it'll be another cylinder 1 miss. I would check compression in that cylinder right away to rule low compression out. You have already addressed the other causes of a misfire.
Please let me know how the compression looks.
Sounds good to me. If your compression is good, and your spark plug and coil are good, and your fuel injector is good, then have you verified that your fuel injector is getting power?
I would check that. alternatively, If you have a mechanics stethoscope then you can listen to the injector to see if it's ticking. We are running out of options here.
still a lean bank 2 code. No misfire code anymore? What is your bank 2 fuel trim?
It runs bad at idle and at the higher rpm as well? or clears up at higher rpm?
Ok. You have more codes on their way. If your only misfire codes from before are cylinder 1, I would suggest checking for injector pulse. You could also do a power balance test where you unplug fuel injectors one at a time while the engine is running to see which one or ones make no difference in the way it's running. Those would be the misfiring cylinders.
Also, if you let it sit for a while, does it run fine when you first start the engine, then get worse as time goes on, or does it run horrible right from the start even after sitting for a bit?