rwj, you need a new shop. I have never heard of a PCM going bad. They are just being lazy and trying to diagnose with the shotgun approach.
Simple question. What is your temperature gauge read while driving? Is it straight up, is the needle a tick to the left, or is the needle a tick to the right?
EXT, you are using the shotgun approach to fixing problems (as exhibited by rwj's mechanic above.) There are tried and true methods to diagnose this code and you don't need to randomly replace parts that are working correctly.
The first suspect is the thermostat or coolant temp sensor. I ask the same question of anyone who is indicating their engine is running rich: is your temp gauge straight up, a tick to the left or a tick to the right? If it is a tick or two to the left as you say, has it been like that for long, and does it wander up and down at highway speeds or is it rock solid to the left?
If rock-solid, it is likely the thermostat. If it wanders, it is likely the coolant temp sensor. (The reality is that they are side-by-side, so you might as well just replace both anyway.)
Also, cleaning the throttle body is good advice, but you only need to change the fuel filter if you suspect bad gas or according to the maintenance schedule. In all my years of working on cars, I have come to realize two rules about fuel filters: #1 - It is never the fuel filter, and #2 - Fuel filters are the most needlessly replaced part oversold by mechanics in America next to nitrogen for tires.
Spark plugs should be changed as they near 100,000 miles and also replace the front O2 sensor at the same time. If you suspect your front O2 sensor has failed prematurely (usually when AC Delco is replaced by Bosch) then get a scan tool with a live readout and find out for SURE. Reading a scan tool will show you not only the state of your front and rear O2 sensors, but also the state of your cat converter.
The rear O2 sensor is rarely replaced because it does not control the engine in any way, and cannot possibly lead to a rich mixture. It is there only to check the performance of your cat.
As for the cat, it will indicate replacement is due long before you get a check engine light. it will start with deteriorating acceleration, especially at highway speeds and less ability to climb hills.
Basically, our rule of thumb in here is to DIAGNOSE FIRST, then start with the easiest, cheapest and most common problem first before spending a lot of money on unnecessary parts.
Good luck and let us know what happens!
:tiphat
