A friend of mine ( Andy ) was a service manager at a GM garage for many years.
Andy started out as a flat rate mechanic.
Andy now teaches Vo-Tech kids how to repair automobiles.
When a young person goes to work in a GM garage, more times then not, if the computer shows no codes, they are befuddled and they run back to the lead mechanic to ask for advice.
We all know that the piston has to go up and down and the valves has to go up and down in time with the pistons in order for the engine to run.
If we introduce spark at the prime moment and we introduce fuel at the prime moment, we will get the maximum amount of power out of the stroke of the engine. Basic knowledge tells us that we need compression, spark, ignition, intake and also a period where there is a dead cylinder - where it performs no work. If all of these events are in time when the compressor is turned off, then it stands to reason that there should be no difference in performance after the compressor is turned on, with the exception of the amount of power that the compressor robs from the engine.
Unfortunately with active fuel management, the events that takes place in the cylinder are not exactly the same for all engines and all situations.
Even things like power options on the vehicle causes the manufacturer to put a computer with a different tune into the vehicle - hence the computers are not interchangeable. 99% of the time, the computer is not a fault.
This leaves upstream and downstream oxygen sensors, crank and camshaft position sensors, knock sensors, throttle position sensors, MAP sensors and a host of other things that can fail, at least to the point of where they do not perform within factory specifications.
Yes, you can use a VOM meter on most, while they are in use - a warm engine, running at speed, but if you disconnect the sensor, it is going to throw a code and put the PCM into the limp mode.
Most good scan tools, even the Snap On analyzers, will do a road test where it will record a period of operation that a trained technician can use to diagnose your problem. If you do not wish to spend the money to have this problem diagnosed, then all you are doing is pizzing in the wind.
The Tech II tool GM uses gives the exact same information.
With the mileage stated, you are going to continue to have more problems, since most problems do not go away on their own.
Might I suggest that you upgrade to a newer model vehicle with no obvious problems.. Maybe the sticker shock of a newer vehicle will shock you back to reality.
