1997 volvo 850 with back pressure problem

my mechanic states that my volvo has a back pressure problem. The car stalled after starting in cold weather, was driven 1/2 mile stopped and let to idle and then stalled. It would not restart. It started again an hour later,let me drive to work and back. It sat over the week end, started no problem, warmed up then stalled at the end of the driveway. Towed to mechanic, started a day later but diagnosed with weak battery and “back pressure” problem my mechanic is trying to figure out why…any suggestions? please, and thank you.

A faulty cat can do this. Fine cold, but highly restrictive when hot. I haven’t heard of it occurring in decades, though.

If your engine is equipped with an EGR valve, I’d check that too. The time line of issue would follow the same contour. If it’s vacuum actuated, applying vacuum to the EGR valve while cold and at idle should disrupt the idle.

Exhaust back pressure can be detected by a vacuum gauge. Vacuum will be pretty much the same under no load for a decent amount into the rpm range. The engine is just spinning out the air:fuel mixture in work. If there’s an exhaust restriction, that reading will drop …hit a progressive brick wall and won’t recover at a stable throttle position.