1993 bonneville obd problem

Hey all...Got a good one...I'm the proud owner of a 93 bonneville with 185k miles. Just got done replacing the engine with a 60k engine from a 94
lesabre...Here's the problem...The car is nearly undrivable when it's cold... idles well, bogs and coughs severely when accelerated ...Once it warms up the car performs well accept for a slight hesitation from a dead stop. The "service engine soon " light is on and off intermittantly, it comes on mainly in traffic/stop start driving. I had a friend (professional tech, 20+years) scan it with his Snap_On scanner and the only thing that's showing is "fault in esc module circuit" and ignition timing seems to have 0 advance till around 2500rpm under a no load rev. This car has been sitting for nearly a year with old gas...we drained as much as possible and drove approx 200 miles with fresh 93 fuel....no change... thought that possibly the engine computer could have problems...replaced it... no change...Once again during highway driving the car performs as well as it ever has??? The technician checking this out is one of the best in the area and this things got us both baffled....HELP!!! Thanx in advance, Gonzo -----P.S., fuel pressure checks OK, low end of the range but in specs
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