Well after more thought on this on my way to work this morning and i started leaning more towards the map sensor being my problem (not that i don't believe you guys don't know your trucks) so i picked one up will out running errands today and installed it. So far problem fixed. Let my truck sit for awhile then started it up and it idled like a kitten for about 20 mins never missing a bet.

 

Mine is doing the exact samethinmg right now. I hooked up a scan tool that reads live data and I could the pre cat O2 sensor only switching between 80 to 150 mv thus giving me a lean mixture. As soon as I break the rust and get the lil F*^Ker out I should be good LOL!! So I suggest checking yours too... Oooops should have read the last part of the thread LOL

 

Ya im gona go ahead and change my 02 sensor as well. Does yours sound like its sucking air around the air intake when it starts running bad? Mine only done it (sometimes) like when i first started it and let it idle for longer than a couple of minutes before driving, but if i drove as soon as i started for about 10 miles and then stopped it wouldn't ever do it. Other than that it ran fine all the time thats what lead me to the map sensor, it was kinda like my blower motor worked when it wanted to.

 

Symptoms seem similiar if not completely the same. When I first start the truck I got a rough idle then it would smooth out and run fine with a few hard revs. The air you hear comes from the IAC (Idle Air Control Valve) at the back of the Throttle body. Mine would do the rough idle on warm starts too. After driving awhile even if I shut off for a few minutes to run into the store. As soon as I started it again same thing would happen. From everything I've learned on here it seems like the pre cat O2 is going to fix it. It controls the fuel mixture and it needs to warm up to work properly. The hard revs cause the sensor to adjust the mixture and it smooths out until the sensor cools down again. Mine however got progressively worse but as soon as I get the sucker out we will know for sure. Right now its rusted in pretty good hopefully will have it changed this week...

 

Mine wouldn't do it immediatly it would start running bad after a couple of minutes sitting idle.

 

That's when the PCM switches over to closed loop mode after giving the oxygen sensor time to heat up. Hint hint.

 

LOL Yup yup that's mine and now if it ever comes out I'll be good...

 

CRC Freeze-Off is the, um, cold ticket for that. If you want it to really work, heat the part first, then soak it with a ten or fifteen second blast of Freeze-Off. Then give it a few minutes to penetrate and it ought to come right out. A bit grumbly-grindy, but it should come out.