longshot.. but adding to what the last guy said.. if its a heat problem, removing the O2 sensors might give you the illusion for a little while that it was fixed, as the engine will run cooler when it runs rich (with no o2 readings, the computer runs the engine rich)..

but im not sure why a cooling problem would make it missfire..

im really pulling at straws, and i'm not an expert on this stuff, so take this advice with a grain of salt.. im just thinking aloud hoping maybe something i say might lead to a good idea..

the only thing i can think of is that the computer might retard the timing if the engine starts to overheat.. but i wouldn't think that would make it miss.. you would lose power.. but it shouldn't miss.. i dunno.. good luck man.. i hope you don't have to sell the car over it.

 

u will start to miss if you get any bad combustion, and then the o2's will try to compensate by adjusting fuel/air ratio and after your running so lean ur gonna start missing, bogging down

try throwing some new wires on there, they might have got chewn up by the pullys, ive had 4 sets before i did ovc wires, each of the 4 sets was good for maybe 10 miles before it got ruined again... i didnt learn my lesson...

since it gets better at about 3500 rpm's its ur fuel/air ratio something is bad either w/ fuel or air lines, or your not getting a spark on a cylinder... and if your o2's are picking up lots of gunk that means your cat will soon follow... so find your problem before your cat gets clogged.

my bet is electric (not opti either before, or after opti) in combination w/ an old sensor which is starting to fail.

do you ever get hot? what does it run at?

 

im no expert, and may be way off, but maybe try the o2 sims, theyll provide a accurate cpu reading always

 

Have you checked any of your EVAP system yet? It's part of your emissions system (the evap canister and valve back by our gas tank and theres also a solenoid on the passenger side of the intake manifold). The function of that will change from cold to hot (cold the EVAP system really doesn't do anything but when hot, it starts working). It can actually cause driveability issues believe it or not. Something to keep in mind if you haven't looked into it. Even something as simple as your gas cap being bad can screw you. Sounds kinda stupid, but don't overlook it. My buddy had a Mecury Sable that would run great when he first started it up, but after driving around and after it sat, it either wouldn't start or run like garbage. He took it to a few mechanics and no help. I had him spend $5 on a gas cap at Autozone and the problem went away. Just some input for you. I would really suggest taking it to a good shop though if you don't get anywhere, cause throwing parts at it can really burn your wallet sometimes. Ask me how I know.

Ken R.