I have a 2003 Trailblazer LT with ~125,000 miles on it currently.
A few years ago, I started noticing a ticking sound in my engine
, a very high idle (sounded like a diesel engine) and occasionally, the Service Engine Soon light would come on. I had a mechanic read the error, and they told me the PCM needed to be reprogrammed, but could only be done by a dealership. So, after about 6 months, with the engine continuing to idle high enough for me to start getting worried, I took it to the dealership. At the time, I could only afford for them to re-program the PCM, but they also suggested replacing the fan clutch & relay.
A few months after that (in mid-February 2011), I had a mechanic replace the fan clutch (and also a new belt). The ticking sound and service light went away, but I still have very high idling and my AC only cools when I'm moving. (At stop lights or traffic jams, the cooling stops.) I've also noticed a decline in gas mileage performance, but I'm not sure if this is related.
I've researched this a bit on the web already, and the suggestions surround re-programming the PCM and replacing the fan clutch, which I've already done. I don't know where to go from here. Please help! Thanks ahead of time. :)