Hey guys I'm new here. And couldn't find a solution anywhere else and I'm hoping to find it here. I swapped a b16a2 into my 99 ek but after I let it warm up for a while the RPMs start going up and down rapidly and when I'm driving and I'm a a constant speed and I step on the gas a little it jerks foward when I let go of the gas a little it jerks again so pretty much there's a point where I can't keep the gas steady. I already changed my throttle body together with tps and map sensor also tried another ecu. And sometimes when it doesn't jerks the RPMs along go up and down fast my car idles around 2k and sometimes it just goes from 2k to 1k. It's weird any help. I was thinking replacing the iacv? Thanks

 

ANY ENGINE CODES!?
The idle speed going up and down could mean a vacuum leak.. I would check the Fast Idle Thermo Valve for leak/malfunction and also check your suggested iacv but I don't think that would cause issue at cruise...
If you can get ahold of an Obd2 scanner and check the conditions that occur at those intervals with the scanner you could possibly see if its leaning or riching and also watch the ignition for any thing unusual

tps could cause jerking hesitation