Super weird high idle issue ka24de

[rv_zenki]

So I've been fighting a high idle issue for a while now. The car is a 96 s14 with a ka. When I first start the car it will idle around 2k for a couple seconds, drop down to around 1100 for a few seconds, then climb back to 2k and hold steady. Once the car warms up the idle will drop down to around 900 then immediately surge back to 2k.

I have a brand new iacv and smoke tested the car. I also replaced the pcv valve. The tps ohms are where they should be. I unplugged the maf while the car was running and it started idling like crap. I have a Bluetooth obd scanner and it shows the coolant and air temp sensors are fine.

I tried adjusting timing however when I unplug the tps the idle goes to about 2.8k-2.9k. I am worried this is messing with the timing.

I'm really running out of ideas here so any help would be greatly appreciated.

[NukeKS14]

Have you adjusted the idle screw in at all on the new iacv? Yeah you need to warm it up and pull tps to set the idle but you could screw it in to lower the idle enough to get control of it so you can get it properly set.

Another common issues on the ka's is people get the dizzy a tooth off. Set your motor to tdc and restab the distributor. Get a timing light and aet your base timing. I had some issues with mine due to the dizzy being off a tooth when i bought mine.

When did the idle issue begin? Did you change anything around that time?

[rv_zenki]

Yes I've tried to mess with the idle screw. Nothing happened. And I doubt its the dizzy being off considering the car was running just fine before this. I didn't change anything.

[TheRealSy90]

With the IACV screw fully closed the engine shouldn't get enough air to stay running.

Sounds like your throttle plate isn't fully closed at idle. Make sure someone didn't mess with the throttle stop screw preventing it from closing all the way. It shouldn't be touching the screw at all really.

[rv_zenki]

I'll try that when I get home from work. Thanks for the replies

[rv_zenki]

So I loosening the screw. The cable bracket isn't even touching the screw now. Still idling high. Is the cable bracket supposed to be able the go down all the way? Also if I pinch the iacv hose the idle goes down. Can get it down to the point where it will stall. I still don't think this is the issue though considering I can unplug it and nothing happens

[NukeKS14]

Sounds like an iacv issue then. The iacv plug goes through a mini harness that runs across the intake manifold then plugs in at the dual gray plugs above your TB. Id grab an FSM and validate what wires they are then do a continuity check with a digital multimeter set to resistance. Make sure the wires arent broken or shorted to ground on the mini harness. Check your connector on the engine harness side and make sure it isnt all crapped up.

No change when plugged in or unplugged but change when you restrict air in to iacv tells me either the iacv is stuck, or the computer is not able to change the valve position. Ill be stuck at home all weekend after i pick my car up tomorrow so ill dig through the fsm and see if there is a fuse or anything else that might have failed.


https://www.nicoclub.com/service-manual?fsm_download=240sx/1996/ec.pdf

Ec-222 and 223 have your harness and miniharness pinouts

10A fuse #23 on the left column of your fuse box by your left foot

[rv_zenki]

Yea I have the fsm. It has power and continuity. I guess the ecu could be sending the wrong signal/ not sending a signal at all. I'll try back probing it and check the pulse width. Thanks for the help

[NukeKS14]

Have you tried to pull codes on the ECU? curious if anything shows there. Disregard your OBD scanner, use the screw on the ECU and the LED lightbulb to read the codes.

There is an AC idle-up function on the IACV/AAC too... wondering if maybe that is stuck open?

https://zilvia.net/f/showthread.php?t=376432

older thread, same issue. Could you have gotten a bad IACV somehow?

last weird thing to look into, IACV regulator.

https://i.ibb.co/gD8wDLT/20180716-141508.jpg (https://ibb.co/gD8wDLT)
https://i.ibb.co/hRVR8Qs/20180716-163826.jpg (https://ibb.co/hRVR8Qs)

guessing you replaced the one on the left (in the top photo) but the other on the right is for cold starts. it could be leaking by too? which plug are you unplugging when you're testing that? the purple one? try that thing too, or even easier, unplug the 2 mini harness plugs above your throttle body and see if that affects your idle.

[rv_zenki]

Yea I've pulled the codes. Nothing pertaining to this. And I know about the AC function. The IACV I pulled off was in fine condition and I assume the new one I put on is too. I have a spare ecu I'm gonna put in and see if that changed anything.

[NukeKS14]

I guess I did my last edit after your post. Check the other valve too. it feeds off of the same throttle bypass hose at your intake.

https://parts.nissanusa.com/p/Nissan_1995_/Iacv-Air-Regulator/89571482/22660-53F00.html

That's the part

[rv_zenki]

I've thought about that being the problem as well. I think if it was stuck open though it would just make the car idle a little above 1000 all the time like its supposed to when its cold, not 2000

[OnTheChip]

You might check the EGR tube for leaks.

[TheRealSy90]

Remove the throttle cable from the adjustment bracket when you're trying to make sure the throttle is fully closed.

Then verify the throttle plate screw isn't keeping the throttle from fully closing.

Then reinstall the cable to the cable bracket, and adjust it so that the cable is not pulling on the throttle, should be just a very slight amount of slack.

In this photo it's the small set screw and jam nut, just to the left of the inner cable pulley. This shouldn't be touching that throttle mechanism tab at idle/off throttle, the part below the screw in the photo. Otherwise it's not fully closing.
https://cdn.shopify.com/s/files/1/0366/9149/products/IMG_2568_29f32c18-717b-4639-a12f-d70a0bc40f54.JPG?v=1571439159

[rv_zenki]

Well I figured it out. Turned out to be the idle air valve under the mani. Not the one on the back. Theres a tiny spring, and I mean TINY, that keeps the valve in the right place and it broke. I drilled a hole in the it and ran a screw and nut through the keep the valve closed. I know its not the "right" way to fix it but that valve is only for cold starts and I don't really care about that. Thanks to all that gave suggestions.

[NukeKS14]

https://i.ibb.co/cN9tNSF/20180716-141508.jpg

The black one from that pic (on the right)? Glad you got it fixed, thanks for updating with the solution.

[rv_zenki]

Correct. I've never read or head about this issue before. Glad I figured it out.

[NukeKS14]

Correct. I've never read or head about this issue before. Glad I figured it out.

it happens. If you ever get an inclination to replace it, I posted a link on post 11 of this thread to the part #. It's just over $110 at courtesy Nissan.

[rv_zenki]

Yeah I saw that. Thanks. I don't think I'll replace it though. The ka isn't staying for much longer.