Our son was driving his 87 744T when it started running very poorly. It runs like there is a bad leak in the intake system. It will run at 2500 rpm and above, but not well below that. The engine stalls easily. The engine also seems to backfire a little bit-the fitting at the brake booster was broken. I have checked the intake hoses and intercooler, replaced the AMM with a spare, replaced the fuel pressure regulator with a spare, and checked the timing. The fuel injection relay was previously re-soldered, and I just replaced the radio suppression relay with a spare. I have not yet tried the fuel injection CPU from my car, or tried the temperature sending unit for the fuel injection and ignition. Before I do this, what suggestions do I get from the brickboard? Yes, it is the original engine wiring harness, and it is rotten and needs upgading. We have three 740 turbos in the fleet, one 86 and two 87s. The problem occured instantly, although this car has had less torque at low rpm than either of the other two.