P0300 & P0430 codes.

[Scott Martin]

Hey cool dudes.
My 99 Yukon with 280,000 miles has the P0300 and P0430 codes, it runs a little rough at idle but nothing bad, it has normal power and still gets pretty good gas mileage. When I park it there's a strong odor of gas but no obvious leaks, when I get on the highway it will sometimes start misfiring at around 50-60 mph and I know it's misfiring because I can smell exhaust or burnt carbon or something. I put a full tune-up on it 2 years ago along with bank 2 upper o2 sensor... I know the P0430 code is bank 2 catalyst so should I go straight to the downstream 02 sensor first or should I check the timing and what not?

 

[df2x4]

My guess would be that the catalytic converter on bank 2 is clogged up and causing both codes due to an exhaust restriction. The P0300 could be lots of other stuff too, but the P0430 is almost always clogged cats in my experience and I could see how they might cause a P0300 misfire and rough idle if they were clogged up enough.

 

[Scott Martin]

My guess would be that the catalytic converter on bank 2 is clogged up and causing both codes due to an exhaust restriction. The P0300 could be lots of other stuff too, but the P0430 is almost always clogged cats in my experience and I could see how they might cause a P0300 misfire and rough idle if they were clogged up enough.

Well I swapped out the distributor cap and rotor because I've had lots of issues with it in the past and that took care of the codes. But my main issue is the shutter on the highway at around 50-60mph, it only seems to do it when I start going up any kind of incline. It will only last 5-10 seconds and then its like it clears itself up and goes back to running fine until the next time. Some days it will do it 10+ times and some days it will do it once. I'm at a loss for words!