Okay, another issue with the cold - not like we don't see enough of those posts this time of year. My '89 745T had an engine transplant early this year (60,000 miles on the donor engine - 160,000 on the body) because of problems with the head and other issues. Anyway, the car ran well until it got booger-freezin'-cold here in Chicago. When it's been below say 20F it starts and may die immediately but then will restart and run fine. The last couple days we've had these 8F - 0 F with -20 windchill. Cold as the proverbial witch's you-know-what. Anyway the latest symptom is it will start and run if given light gas immediately after turning over but if left without giving gas the idle will surge up and down and it will usually die. Once it warms up it's fine. This morning I get the surging idle but it eventually evens out and I get to work no problem. This afternoon I'm driving out of the parking lot and the car starts bogging severely with a backfire if you give it too much gas. It will allow you to slowly work your way up through the gears until you get it to around 45-50mph where it seems to run okay but any application of throttle sends the boost gauge up into the yellow and the bogging down reappears. An issue I neglected to address before it got too cold to work on the car (apartment dweller - no garage/no heat) was replacing the fuel pumps and filter. The intank pump is Bosch but the previous owner used some el-cheapo Brand X piece o' junk main pump. One of my mechanic/volvo guru buddies said he thinks the car has been running somewhat lean because of the junky main pump. So, it looks like I'm taking the bus to work tomorrow. Any ideas of where to start looking? Newish repairs: new cat, plugs, timing belt, most of the electrics (ie. coil, wires, cap and rotor, etc.)

Thanks,
Matt