simple tune up turns into $1000 PCM??!!?

Need quick help! 2000 Jeep Cherokee Sport w/approx. 87,000 miles… check engine light has been on…. had a fuel system tune up done, light still on. Whent to auto parts store and they ran a diagnostic for no charge (a shop was going to charge me $90 to "run a diagnostic"). codes auto part store got were P0505 idle air control valve and P0303 misfire on cylinder 3. They recommended a tune up to start with. This morning left it with the Jeep dealer purchased from 2 yrs ago and asked about a tune up and check for check engine light reason, had also told them the codes from auto parts store. Got a call at work that Jeeps computer (PCM) needed replaced before they could go any further. They quoted me $551 just for the PCM. In addition there would be shipping and handling to have it shipped from the warehouse in Boston, Mass plus labor for a rough ball park estimate of $1000 just for the PCM part and installation. I asked about the tune up (new sparks/plugs, wires etc) and they said they couldn't do anything until they replaced the PCM. I started google searching and calling around getting quotes on PCM's. The feedback is very conflicting. As for new PCM's I've been quoted $492 - $565 from different dealers who all said they would have to order the PCM from the one and only warehouse in Boston Mass A few auto parts stores said they could sell me a used PCM and one said they could send the current PCM in for repair. I called back the dealer where the Jeep still sits and they said you cannot repair a PCM and you cannot buy a used one or if you do you will have more problems than before because it would be programmed for another Jeep. They then told me that the new $551 one they were recommending I purchase would have to be programmed. I guess I'm a little skeptical. This same Jeep dealership passed the Jeep inspection on 7/8/06 with the driver's side headlight not working! By the way, the 2 year warranty bought at purchase time expired 7/22/06. Now 8/1/06 I think we need a simple tune up but they're telling me we need a new computer (PCM) that ours is shot, it will cost about $994 and then it still may need the tune up and/or other work as well. Any help or advice on this, anyone? Thank you

Well you have nothing to lose by giving it a tune up, as for the PCM i would take it somewhere else and have them look at it even the jeep dealer could be wrong and they are just trying to sell you something you dont really need

Um, they passed you for inspection with a headlight out. I think that's a pretty good commentary in general about the dealer where your Jeep is.

I'd find another shop.

Get a good tune up on the vehicle and see how it runs.

Sometimes the check engine light will come on if your gas cap isn't sealing properly. Some shops will be able to test your gas cap, or you could just replace it yourself for under $20. Beats the hell out of paying some scheister dealership $1000. Don't let them con you!

After the plugs and gas cap, post back and let us know how it's going.

^ the gas cap problem can lead to getting ripped off.

Yeah, it can. Which is why it's worth it to go buy a new one at the local auto parts store and install it yourself!

Thanks everyone, we're going to try a new gas cap and tune up and go from there. I'll let you know how it goes. Thanks again!