bad computer?

[johnnybate]

heres my problem, car info and mods are listed in my sig. car is auto with ~122k on the odometer.

the car flucuates RPM off-throttle, such as if im driving and let off the gas, you can hear, and feel the engine surge a little and the tach will show the RPM jumping from about 700 up to 1000 and back again. also if i shift into reverse, the RPM will drop below 800 and sometimes the car will stall.

i thought it was a alternator problem, but after some tinkering under the hood i realized if i disconnect the battery, when i reset it, the problem goes away for a couple days, and then gets progressively worse.

is it possible its an issue with the computer? if so, what are my options when it comes to replacing it?

i appreciate anyone taking the time to read this, and any help/insight to the problem would be great.

thanks in advance,
johnnyb