vermena

Need some advice. Im working on my 97 Tahoe and I am getting a code P300 and 420 Miss firing of cylinders and catalyst. I did a tune up about 3 weeks ago changing the spark plugs, wires, rotor and distributor cap and the check engine light went off. It has recently turned on.
When I did my tune up I looked at the spark plug and it had carbon suet on it. I checked the sparks plugs this weekend and the carbon is building up again so I believe the engine is running lean which is causing the spark plugs to build up carbon causing the code P300 miss fire.
The 420 code is catalyst but I weary of replacing the cat right now. I don’t feel like paying 500 dollars right now. I have a bad cat because I can hear some stuff rattle when I rev my engine in the tail pipes but my concern is fixing the code 300.Ivechecked some sites about a p300and it says a cat could be the problem. But before I change the cat I believe the issue is the car is running lean and I don’t think a Cat causes that issue.
I am thinking to change the O2 sensors or to do a fuel injection cleaning. I know my air filter is good. What I was going to do before I got the error codes was change the ignition coil, egr valve and to a induction cleaning. I didn’t get to that when I did my tune up. Any Advice would be helpful.

golfer

Your problem with the P0300 misfire is likely due to your problem with the cat.

Your O2 sensors are likely signaling the ECU to lean out the fuel because of the faulty cat.

You may have to bite the bullet and change the faulty cat .