Help please
 

Background, I have a 99 LHS w/195k miles, 200k service was done just before it broke down, my wife was driving and it died on freeway, would crank good just would not start, I had it towed to chrysler, they moved a fuse from the hazard circut to one that was blown out (dont know which) they separated a couple wires on the air management valve where the oil from a slight leak ate the wore coatings, their diagnosis was the whole wiring harness was contaminated and needed replaced to the tune of $2300, for that they charged 100.00, I said no thanks and had it towed home.
a year and half later I patched up the wires going to the air valve, charged the battery and it cranked right up, I have run all the old gas out, put in new and some berrymans, The CEL was on, I had the codes read, I had a cam sensor code, bank 2 oxygen sensor code and one for EGR Valve, and IAT sensor.
It runs and idles good with 1 exception at 2800 rpms it falls off to about 2400 then runs back up to 2800 and falls off, it does it exactly the same both under load driving and under revs idling,

I'm just wanting to get it running right for to give to an in law who has no car, I'm not really wanting to keep pouring money into it

best chance of cause anyone?