The check engine light has been on for over a year now and my mechanic, the dealership mechanic and even another Volvo mechanic are all scratching their heads. The car is an 850 glt and now has 130,000 miles.

Originally, a year or so ago, the car was hesitating/bucking on the highway and the light first came on and the adventure began. I assume it went into limp home mode shortly thereafter. One of the mechanics reported trouble codes relating to a throttle sensor and he played with it and supposedly swapped it out to no avail. After clearing the light, it came back on before I left the dealership.

The other techs have not been able to find any trouble codes nor have they been able to permanently reset the CE light. The car seems to run fine with an occassional (every other month) occurrence of rough idling and in town driving (buck/skip). I'm sick of looking at the light and I've given up on the mechanics. I've decided to follow and troubleshoot the problem myself. I've checked all the service bulletins and, in the absence of a stored code, have tried to address what seems obvious (clean injectors, fuel, general tune-up, check vacuum hoses, etc.). My questions at this point...

1) My model appears to have both an OBDII connector in the cab and the Volvo diagnostic sockets under the hood - will both locations report trouble codes if I use the appropriate procedure (ie. button sequence for one and OBDII scanner for the other)?

2) The diagnositc socket reports 1-1-1 - although the engine light remains lit. Any suggestions for other diagnostics to undertake besides using the underhood diagnostic socket/led code reader - ie. any recommendation for OBD scanners or software for real time monitoring without spending the equivalent of a downpayment on a new car?

3) Any other suggestions/tips of what to check or do next would be greatly appreciated?