I have an '89 chevy with a big problem. I recently swapped the tired old 305 for a 350 small block that I had bought from a local shop. It was a newly rebuilt vortech small block from a '97 chevy. I put on pre '87 stock chevy heads and a holley pro-jection adapter manifold along with a stock 350 throttle body. All the sensors are hooked up and I just today checked the timing gears and everything is right on. I have no fancy scanners or anything but the computer is reading alright with no lights on. The motor idles rough and almost dies. With slight pressure on the gas pedal it seems to run fine but going down the road it will pop and cackle and fall on its face now and then. Any suggestions?? I tried jetchips but they were unable to help me with a chip nor could they suggest any solutions. Any advice will be appreciated thank you!

 

check timing.

 

i have checked it multiple times it jumps around and is different every time i check it. It jumps at an idle when the motor idles up and down but i can't tell if the jump is causing the motor to idle up and down or vice versa

 

so it's still throttle body injected? if so, i'd check the idle air control valve and egr. make sure they're clean and hooked up. the idle air is mounted to throttle body, egr should be back by distributor.
also, did you make sure the timing bypass wire is connected? should be a single tan wire, unless you have vacuum advance on distributor.

 

My egr wouldn't fit onto this intake so i slapped a block of plate on it because i was told that it should run fine without it by the shop i bought it from and I believe i have all the wires hooked up but i will double check that thank you