My friend has a 90 Civic DX hatch, that had a LS motor in it when he got it. It ran alright for a while until he managed to mess it up, then the car would idle funny (like the TPS wasn't set right, there wasn't enought coolant, or there was something wrong with the IAC) but i checked everything and it all was fine. It also lagged really badly when you stabbed on it and I never figured out what was. It got really bad so while his car was in the body shop, he had these idiots change his head gasket. After that the motor smoked like i have never seen a motor smoke before. He talked the shop into buying a new motor for him since they messed his old one up and just yesterday after a couple months i was finally able to drop it in. The retards that orginally put the motor in did a really shitty wiring job so i decided to just rewire injectors 2 and 4 and the CYP, otherwise i didn't change any wiring. When we started the motor up it idled normal for awhile until it began to idle weird again. There is no CEL but the ECU still throws a code 14 for IAC. When his car had the old motor in it, it still did it but it has been disconnected to for 2 months and it still does it. The thing that gets me is is when i disconnect the IAC it still has a weird idle. The only thing that seems to fix the idle is if i pull off the TPS plug let it sit for a couple seconds then plug it back on. Then it is fine till you turn off the car then turn it back on. It can't be the coolant level because I have the fast idle thermo valve bypassed. I don't know but if anyone has any ideas i will definately look into them. Thanks in advance.

 

I saw a car with a weird idle. It would go up to 2 grand and back down, few seconds later, back up to 2 grand and down... and on and on.

The coolant/temperature sensor was bad, causing that weird idle.

Good luck