Cel question
 

ive noticed a pattern in my truck. i have an 0442 code that comes up everytime i clear it. not all that worried about it but what i have noticed is my truck runs like crap everytime i clear the code. as soon as it comes back on (sometimes a day sometimes a week) i have much better throttle response and my exhaust sounds way better. can anyone explain this? does it happen to any of you guys? thanks

It could take the PCM a while to relearn your truck. I know when I go to clear codes the scanner warns that the vehicle may run a bit crappy after clearing.

Why don't you try diagnosing the problem instead of just clearing it...?

lol valid point. ive tried to find the source of the problem a few times with no luck. but on that note when i do figure it out my truck is gonna run like crap once the light stays off. doesnt seem to matter how long the light is off it still doesnt run as good as when the light is on. when i reset a code is it reseting the entire pcm?

Yes.

Also, once certain codes set, the PCM goes to predetermined maps basically ignoring some sensor inputs.

P0442 - Evaporative Emission Control System Leak Detected (small leak)

its got to be the evap canister, ill crawl under and have a look tomorrow. someone once told me when cel is on the truck will ignore 02 sensors. is it possible i have a lazy 02? or does that not make sense

Run a search on P0442. There are a few different somewhat common causes for this code. #1 - the gas cap. #2 - the vent solenoid valve.

You could have another problem. Diagnosis is the key though. To determine whether the O2 sensors are working properly, they should be monitored with a capable scan tool.