High idle (yes, I've searched & read plenty)

[coldblooded]

So I recently swapped in a fresh KA24DE (~40k miles, spotless motor) and swapped from auto->5spd in my 93 SE. From the first time I started it up, it's been idling in the ballpark of 2k RPM. Sometimes it sits at 2-2.5k, other times it bounces up & down (varying rates) from 1.5k-2k. When it's really warmed up & sits at a light for a minute sometimes it will settle into a 1.5k fast idle.

1. ****ed w/ TPS...looks like auto vs manual is different. Yanked throttle body, made sure butterfly was closing good, and put auto TPS on there (it has an extra plug for closed/open throttle). This, of course, made no difference. Adjusting it up or down changes characteristics of bobbling and increases RPM, but never drops below 2k.2. Visually inspected for vacuum leaks. Noticed a solenoid on the back of the drivers side was broken, hose bib broke off probably when dropping engine in. Replaced solenoid (from old engine), replaced hose. No difference, of course.3. Tried adjusting IAC valve. Upon disconnecting TPS, idle shoots to 3.5-4k, IAC adjustment makes no difference whatsoever (screwed all the way in or about to fall out). Removed IAC adjuster screw, sprayed screw & hole w/ carb cleaner. 4. Tried checking air regulator (put channel loks between intake runners & pinched hose that goes into it). No difference, to my surprise.

Any ideas? Seems to me like either the air regulator is fuct, or the butterfly is somehow not sealing well enough to actuate the idle air control. I can't find many more ideas from the FSM.I have an AIV/PAIR removed (vacuum lines capped at throttle body), Injen intake (AIV extras & everything capped/sealed appropriately). ECU is still from the Auto, clutch circuit is shorted for ignition. All else is stock besides the lower heat shield being removed. No CELs or other problems. All electrical connections were checked relatively well when swapping. Engine pulls like crazy & runs amazingly in all other situations.

[djhpr]

http://www.nissanperformancema...arah/

That might help a little (ECU issue)

[coldblooded]

Interesting. That would make sense...I've been hard pressed to believe that a known good running motor would have defective valves/sensors, etc.Looks like I'll pick up an ECU this week...pretty cheap attempt for fixing it.

[Dattebayo]

You forgot one step in checking sensors and its easy. Check the O2 sensor. That can cause a high idle too. You really have to remove your iac/aac valve to check it to see if it is stuck open. Any engine that sits around for any period of time can have electrical/sensor problems even if it was known to be a working engine.

[coldblooded]

Good point on the O2. I didn't realize it could affect the idle that drastically, but I guess it's worth swapping to see. Usually the CEL will come on if the O2 is that far out.

I've got my fingers crossed that the ECU will straighten this out, although I'm not betting on it.

I may swap the AAC assembly since that's relatively easy until I get the ECU (probably get it off ebay, local JY prices are stupid).

If none of this works out, I'll be pulling the air regulator to check them/swap it out. I'm putting that one off, since I have to pull the intake off to get it out.

Sure is nice that I saved the old engine for a while...nice to have some of the small parts to test things out.