Alright Gents,

I have searched these forums for the past two weeks and couldn't locate a fix so far. I'm having an issue sorting out a high (1750 rpm) idle, as well as a rich condition. Here's what I've done so far- removed/cleaned IACV, removed/cleaned FITV and tightened plastic collar inside FITV, cannot find any vacuum leaks (hooking up to vacuum gauge later this week to verify), bled coolant system.

The car is a 91 DX hatch with:
Hmotors B16A - OBD1
PR3-J01 ECU (factory, came with Hmotors B16)
Monotech USA built, plug and play harness
A/C and P/S deleted, Skunk2 IM, Skunk2 Header, AEM intake, Skunk2 Radiator, Mishimoto slim fan etc..various other bolt ons.

I lost fuel when diagnosing a week ago due to my fuel pump going out. It has been replaced and I've got fuel back. Should be running factory fuel PSI/specs. No fuel rail, FPR upgrades.
I pulled my (new) NGK plugs last week when figuring out my no-start and they are extremely sooty. My header just dumps through a turn down at the header outlet and there is a fair bit of soot on the garage floor as well as a rich smell when running. I do not have a wideband to monitor AFRs.

I unplugged my IACV while running, but not at operating temp, and my rpm did drop to 11-1200 rpm, but thats still on the higher side. Tightening the collar in the FITV dropped me from 2k to the 1750rpm it's at now. The motor *shouldn't* have had the idle screw played with so I haven't played with it yet. When I first fired the car after the swap I threw a CEL for TPS. A new TPS has been installed and calibrated. I currently have no CEL codes. Purrs like a kitten, just higher than normal.

If anymore information would help, I'll get it to you. I just cant figure this out no matter where I dig in the forums. I promise I've been trying to not make this post.

Thanks for any help/info in advance.

 

It should be much lower with the FITV off, around 5-600 I believe. With the FITV off, can you bring the idle down with the idle set screw?

Is the throttle closing fully? Is there enough slack in the throttle cable?

 

I adjusted the throttle cable, which was initially a tad tight. That dropped me from 2200 or so to 2000 rpm, it is now good to go. When I tightened the collar down inside the FITV it dropped from 2k to 1750, where it is now. I haven't adjusted the idle screw yet. The only reason being with the high idle and the rich condition, I figured both issues were being caused by one source problem. My concern is that I'll get the idle down with the screw but that wont be my root issue and that'd be more of a band-aid. Does that make sense?

 

Disclaimer: I'm speaking from experience w/ idle issues on my car with Hondata S300; I think the same should apply but not 100% sure.

If you unplugged the FITV and it dropped to around 1000, adjusting the idle screw should lower it. If it doesn't, you may still have a vacuum leak somewhere.

Also try clamping down the vacuum lines and observing the idle. You may have a bad PCV or leaking brake booster.

If you can get the idle around 500 with the FITV unplugged you are good with leaks / idle settings.

If its plugged in and warmed up and still idling high, maybe there is an issue with a coolant sensor. On cold start the ECU idles higher and runs richer to aid with warm-up. Once it reaches operating temperature the FITV should adjust the idle down to around 900.

 

I unplugged the IACV. That caused my rpm to drop, same when I just cover the IACV port inside the throttle body. The FITV only caused a 200 rpm drop once I tightened the plastic collar inside.

When I swapped the motor I went through and replaced all vacuum lines with new line. Lines going to the brake booster are old still but I cant source a leak in them. I'll try and get this hooked up to a vac gauge towards the end of the week and see what I've got there.

I'm not trying to nay-say your help BTW. I appreciate the feedback.

 

Ah sorry, neither of my engines had a FITV... I thought you were talking about the IACV. I know what they are now.

The booster or PCV could still be leaking, you want to test those by isolating them from the engine by clamping the lines.

The FITV is a mechanical valve that adjusts idle when cold... if you are still having an issue after ruling out vacuum leaks I would suspect it and maybe try finding a replacement. I'd say remove it or swap in a newer throttle w/out it, but cold starts wouldn't behave the same as normal.

Best of luck.

 

Appreciate it man. I'll give it a shot.

 

*Update* I'm showing about 17in vacuum at a 1750 idle. From what I read in other posts, 18-22in is alright at normal idle.

 

The vacuum looks good so long as its stable.

I'm still suspect of the FITV; When you cleaned it, were you able to confirm that coolant can flow through it? The FITV won't close and bring the idle down if it can't get warm enough. There may also be air in the system.

At this point I would fashion up a block off plate and take the FITV out of the equation entirely. If it helps, great; But if not at least you've ruled out one possibility.

 

Fair enough, might as well give it a shot. Thanks.