My 89 240 (240K miles) is my backup car, so it doesn't get driven all that often. A few weeks ago, I started it after it sat for two months (after getting a new battery). It ran really poorly, surging and then losing power so I could barely accelerate. I stopped at a gas station, checked under the hood (everything seemed fine) and filled up from half a tank. Restarted it to drive home, and it ran fine. Today, identical scenario after it sat for a week. My boyfriend was driving it inbetween, and said it occasionally ran poorly, but would run fine the next time without him doing anything in between.

Now, this car hasn't really idled properly in years (and it still doesn't), but an AMM and cleaning the IAC have helped a bit, and its livable (shakes at idle, stalls on occasion). However, its really undrivable when it does the surging/lose power thing. Any ideas here?