high idle, trying to pass nazi ca smog
 

The title says it all, I've been trying to clean the iscv with carb cleaner, checked the air valve, used magic diagnostic mode, trying to set the idle but can't get it to go under 1000rpm with the idle screw all the way in, which ca dislikes and prevents me from passing smog. Figured I'd ask on here if for other suggestions before I replace the iscv. This is on a 92 project I just picked up, only other thing I can think of is the neutral wires on top of the trans could be shorted, but they appear to be connected. The idle is pretty smooth otherwise, searched for vacuum leaks and haven't found any so far. kinda think it's the iscv, but please let me know if I'm missing anything else. just want to smog it, sell it, and get a supermoto :drool:

Replace the throttle body...
http://www.miata.net/garage/isc.html

Not sure if thats available on the older miatas, but have you tried setting the idle with the screw on top of the TB?

If that is open too much, the ISCV is not going to help...

Yup, have the screw all the way in with the car in diagnostic mode and the screw functions as it should (idle progressively goes up when it's backed out), but the idle does not drop below 1000rpm at the bottom of the threads.

I've been using the miata.net link above, trying to isolate the problem but the only thing i can think of is the iscv as everything else seems ok. Guess I'll start looking around for a good used one...

I had pretty much the same problem on a car I was working on. I tried a few things in an attempt to save it but ended up just replacing it. post an ad in the f/s section. I have also had good luck with www.car-part.com, it searches local junkyards.

occasionally they sell cheap throttle bodies with the IAC still attached on ebay.

thanks for the tip, I'll check the forums first then prowl ebay

Well I replaced the ISCV and now it idles at 2000rpm.. Still can't get it to go down in diagnostic mode using the adjustment screw. Any other suggestions? Could it be a problem with the ECU? Would a small rip in the throttle body gasket cause this? Same goes for the tb to iscv gasket.

The old iscv was nasty inside and looked really clogged, but maybe that was keeping the idle at 1k instead of 2k with the clean iscv? I'm running out of ideas and really need to sell the car.

yes you have a leak

Go oldschool. Get a can of carb cleaner and start spraying the joints where the gaskets are. Start directly after the MAF and work your way to the engine. Shoot the ISCV, throttle body, around the injectors, manifold to head connection... basically anywhere it might leak. If the sound or RPM of the motor changes, and its repeatable, you found your vacuum leak.



Don't be stupid and flood your electronics or engine bay with cleaner, that would be a bad. Short controlled bursts directed at the joints will tell you what you need to know.

Thanks for the tip, I'll give the oldschool method a shot

Hmm, no luck so far spraying around for leaks. I'm starting to think this is still an electrical issue. I unplugged the tps and iscv while the car was running then plugged them back in and the idle dropped back to a steady 1k, then went back up to 2k when I touched the throttle. Guess tps is the next thing to try replacing, that and more gaskets. Are there any other electrical components I could be overlooking?

edit:

now it's really looking like the TPS sensor. I tested resistances and saw continuity between the top two terminals at WOT as I should, but didn't read continuity between the middle and bottom terminals, regardless or throttle position the resistance didn't change.

Also found a small vaccum leak at this 3 way valve that goes to the evap canister. I'm tempted to just ditch that little 3 way valve and plug the vac lines together going to the evap so the car still passes visual smog check.

Well, it was worth a shot. What happens when you pinch off the evac line?

the idle drops like 50rpm lol I just looped the vac lines on the front of the intake manifold together to rule out the leak for my idle problems. I'm almost positive it's an electrical issue since the idle is stable at 2k or 1k, but has that crazy range of fluctuation depending on what is plugged in or not.

I should have just replaced the TPS, ISCV, and TB together at once...

Most annoying part, the car is running better than ever except the high idle.