I've swapped a 87 305 tpi into a 85 z-28 because the original motor had a cracked block (leaking coolant into oil). The original 305 ran smooth and revved up good so I assumed all of the electronics were good. I had to use the lower intake from the 87 but everything else came off of the 85. Now with the 87 motor installed it revs out good but falls on its face when it drops below 1000 rpm. I've already ckd the tps and iac sensors, found a hard vacuum line cracked and fixed it, and it had a 34, 43, and 44 code active intermittently. Any ideas?