I have a 91 PA with 136,000 miles. It has been sitting 95% of the time for the past year (Grandma's car). Drove fine for the first 2 to 3 weeks, but now the Service Engine Soon light comes on and goes off, comes on and goes off. It has knocked off on me twice, but cranked right back up. I think it has something to do with sitting for so long. What can I do?

You need to download the fault codes that is causing the "check engine soon" light to come on. That will pinpoint the failing sensor or circuit.

Instructions can be found at this link: All that's needed is a jumper wire.

http://www.geocities.com/dann8785/serviceenginesoon.html

Could be a bad or dirty Oxygen sensor. They tend to get slow or flaky when they are left sitting for a while. If the car hasn't been tuned up in a while, defineltly start there. check all the fluids etc.