hardwater

Purchased this car from a private seller a two months ago. Recently the "Check Engine" light came on, but car still ran fine. Our mechanic checked the codes and reported, "Misfire on cylinders 3 and 4." He suspected the coil or dirty injectors, we elected to fix next paycheck so he reset the computer so the light went off.

One week later when I started the car the idle was high at 2k, reminded me of a stuck choke on older cars. Even after a short drive around the block the idle stayed at 2k. I turned off and let sit for a day. Next day start, idle still high at 2k. After 60 seconds idles slows to 1k and "Check Engine" light comes on. A short drive reveals very sluggish performance, like I was driving in 4th gear when I was only in 2nd gear. I parked the car until I can track down a repair manual or save $ for trip to mechanic.

Any ideas?