I Just finished my swap (b18a1 into ej8/97coupe). i used my old obd2 harness to wire the motor up and everything seems to be in place but i have a VERY jump idle it revs up to 2k then drops to like 700 and just keeps doing that. sometimes its stable but its still high 1300-1500. i thought i had a vaccuum leak so i check all the hoses and they seemed to be all there and in order. then i remembered my throttle body gasket was bad so i changed it but it was still happening. now my IAT sensor (i think thats what its called, the whitle plug on the intake manifold) is not hooked up could that do it? any suggestions would be greatly appreciated, thanks in advance.

 

could be the TPS or the IACV valve

 

you used an obd2 harness on and obd1 motor? problem solved.

 

Mine did that for along time before i changed it. I changed the Idle Air Control and that wasnt it, then i changed the Fast Idle Valve and that fixed it. Good Luck!

 

When does it do this, all the time, when it's warm, cold, hot outside, cold outside, curing a hot start, etc?? What ECU? Saying it idles funny doesn't say anything about when or why.

And yes, the IAT should be hooked up, it's a pretty important sensor. If you don't hook it up, the ECU will default to a preset air temp value which could be completely wrong obviously.

 

problem solved it was the fast idle valve