98 Civic, replaced motor and now idle fluctuates up and down
 

I bought a 98 Civic EX with a blown motor, so I found a 98 HX (also vtec) and replaced it, and now Im getting a fluctuating idle 1200-2200 rpm's. I didnt find any vacuum leaks, and now the check engine light is on, anyone have any ideas what could be causing this? I did tap the isc on the tbody and it didnt seem to change anything. Im a DSM guy and I dont know jack about hondas. Thanks

iac? i think thats what its called. The sensor for idle air control or something. My neighbor has the same issue with his early 90's prelude. it annoys the hell out of me. Every time he starts his car i gotta listen to it with his loud ass exhaust

I don't know much about hondas either but thats what I would check

well, did you swap the PCM too? they should be different. what code is it throwing?

I kept the original ecu because the only thing changed was the block and head. I used the original manifold and whatnot. Plus the manifold off the new engine had a bunch of emission crap on it, that my car was not wired for. As for the code, I have to scan it.

I believe the IAC motor will stall a car out if it isn't working properly or clogged. It will start and run for about a second then stall. I am betting on a small Vac leak or emmision failure. Get a gauge and an adapter and see how much vac it is pulling at idle.

its ur TPS Sensor, take it off unplug it and put it back on. should fix it right up common problem, or it could possible be broken and need a replacement. Or make it real easy and check ur check engine light. heres a link to help u do that http://www.honda-tech.com/zerothread/1901557:banana::banana::banana:

i've had distributors go bad and do some crazy **** like that. i have one laying around if that ends up being it.

Thanks guys. Im gonna do a leak down this weekend to see if I can find a vaccum leak.

It's probably not your distributor, iac, or tps. My money is on the FITV (fast idle thermo valve) IF it's not a vacuum leak. You said you swapped intake manifolds right? Take a can of brakekleen or soapy water water and start spraying around spots that could have a leak. If the surging stops for a second or two, you've found your vacuum leak. If that's not it, pull the fitv, it's under the throttlebody, pop off the end with the two screws and screw the plastic plunger back in all the way tight. These can come loose over time and cause the surging.

Did you get all the air out of your coolant system? If you have air pockets in that it will cause your iacv to act up.

I used the original intake manifold off the car, not the donor intake.

dude if u have a check engine light CHECK IT!!!! it would make this soo easy:screwy::screwy::screwy:

exactly. where are you from? ill scan it.

I would say start by cleaning your IACV (idle air control valve) its on the back of the manifold. Or if you have the old one try that. But if you have a check engine light you should probably start there. Stick a paper clip in the blue plug above the ecu and watch your check engine light blink and let us know how many times. Good luck!

I linked you up early in the post here it is AGAIN http://www.honda-tech.com/zerothread/1901557

Im gonna scan it this weekend. I will let you know what happens.

Dude, lol.

EX and HX, although both VTEC, are not nearly the same. EX is standard VTEC, high cam low cam. HX is VTEC-e, COMPLETELY different. You're going to want the ECU for the HX, that's why you're throwing the code and that's why the idle sucks so bad.

****, if you need a D16Y8 (the EX engine), I've got 2. :P

I did get the HX ecu, Im gonna check the code, worse comes to worse I will swap out ecu's.

wow ummmm.....explain what the diff are plz!!