Hi, I am having a whole slew of problems with my 2000 Sunfire GT.

I will start by listing the problems

-no more indication for rpm, speed, fuel quantity or engine temp on the dash,
-sometimes the mileage is displayed, other times it just says 'error'
-Plenty or error codes when checked for OBD-II ie, P0107, P0108, P0122, P0300, P0302, P0440, P0480, P0502, P0507
-rough running when at idle, and some form of tweeting sound, indicating misfire in the engine
-radio will work when stopped with no headlights, wipers or heating; but as soon as any other electrical is turned on the radio turns on and of non-stop. Even braking (initiating the brake lights) can trigger the radio to restart.
-high rpm at idle when starting the engine, sometimes as high as 2500 Rpm. As the engine warms up the idle rpm decreases gradually until about 1100 rpm

So, I am led to believe there is something wrong with the computer, which I am thinking of replacing as a 1st step. A few months ago it fell from where its supposed to be and started grinding against the front wheel after I hit a speed bump. A garage welded it back in place, but since the electrical and gauge related issues started to surface.

There maybe a well be an issues with the engine timing or vacuum system, but from what ive read that is all regulated by the computer so maybe I should start by changing the computer altogether and see if the engine errors persist or are fixed by replacing the CPU.

Also most ECM's available online specify they need to be reprogrammed locally... which means I have to visit GM to have the work done?

Any advice to help me decide what to do would be appreciated!
Thanks

Look at your wiring harness before you replace the computer, you could have a bad ground coming from the pcm.