hey i just swapped a 87 motor into my 90 pickup andi just started it it pulses when it idles pretty bad but on the gas its normal ive replaed the throtle sensor and checked my vaccum lines and i cant figure it out please elp just throw some ideas at me

 

timing?

 

I just did the same swap in my 89 and had the same problem. Make sure you use the tps for your truck and set it up using an ohm meter to position it correctly. This is the info I used.

http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

My engine runs great now, but I do notice a little up and down idle when I come off the throttle with the clutch in. If I tap the gas a few times or let the clutch out a little, the idle falls to where it is suppose to be and idles smooth. I also noticed at a little over half throttle the engine feels weak.