Bought a proj truck for stepson. Buddy who sold it to me replaced a bunch of parts before finding the timing chain bad, once running good had rod knock. Truck came with a 97 S-10 I4 motor and trans. Stripped both motors and swapped all parts from the GMC to the S-10 long block including the intake (complete) and exh manifold(different flange...), all sensors except the crank sensor-there is a sensor on the S-10 that is not used (not present) on the GMC and is in the way to use the 90 degree GMC crank pos sensor so left the straight S-10 sensor. Truck started right up! Runs good and drives great but has a high idle. Am well versed in Mustang EFI but wanted some guidance on the GM stuff. Throttle plate is completly closed at idle and is sucking air through the hole in the top of the throttle body. It shuts off oddly-for lack of a better word-violently. In the last second when it is shut off, I can hear it sucking air violently and the motor shudders to a stop, but starts up fine. No CEL, but no GM scanner either! and no platesyet so can't take it to aparts store yet. Hand every vacuum line and checked for cracked and dryrotted hoses. We have not reinstalled te A/C, but I did mount the S-10 compressor so I could get the serpentine belt on, the GMC compressor has two electrical conectors as well at the clutch connector, not sure if the computer is seeing/not seeing a signal due these two conectors that go in the back of te compressof not being hooked up. Would appreciate any help possible.