I have for more than a year had intermittent problems starting my '97 850. It started when I bump started it on a hill leaving a filling station April 2004. The engine light when on and the car tachometer would surge to 2000 rpm, then drop to a very low idle, then up, then down. The car would cough and buck. Long story short, after trying everything, I found that if I left the car off for 20 minutes or so, it would sometimes start and run fine. I later found that by disconnecting the battery for a few minutes, I could get the car to start without problems. This continued for some time, then suddenly, stopped happening for 8 mos. or so. It has now begun happening again, first every week or so, then every other day, now it happens everytime I run the car, shut it off and attempt to restart it. It doesn't start at first, but then will start and buck and surge and will have no power, backfiring (sound like a lean miss). I now find that even with disconnecting the battery, it doesn't always cure the problem on the first disconnect, but takes now a few (3-5) tries. I am totally frustrated.

Please advise. Should I buy a code reader? IF so, what reader should I buy and is there a least expensive reader that will work on a volvo 850. Experts, can you help me out with this problem? Thanks.