S14 KA24DE super high idle? (4k+ RPMs)

[Own]

Hello everyone,

Was wondering if anyone has had any experience with a really high idle KA24DE. When I turn on my S14, the RPMs shoot up all the way to the 4K RPM mark and then sometimes either completely idles there or still begins to shoot up even higher.

I've replaced my MAF and IACV Valve (w/ new gasket) but no change.

Have also sprayed the manifold with non-flammable brake cleaner to see if I could find any vac leaks but have not noticed anything abnormal there.

Any other ideas? :bowdown:

(have checked older posts but they seem to not lead anywhere or point to MAF/IACV valve)

[Silv1401]

Vac leak. When I got my s14 it had like 3 or 4 vac leaks, and idled at about 4-5k. Mine was turbod by previous owner and then garaged for a decade. They disconnected EGR (but left everything in) and the vacuum tree between the firewall and intake manifold was completely open to atmosphere, there were also two vac ports on the side of the plenum that were completely exposed. I would also check along the intake, and maybe the brake booster line. Fwiw I tried using carb cleaner to find my leaks, and it never worked.

Sent from my SM-G950U using Tapatalk

[NukeKS14]

second the vacuum leak. I have better luck finding leaks by pressurizing the intake manifold with the engine off and using soapy water.

https://www.nicoclub.com/archives/use-nicoclub-coms-factory-service-manual-database.html

the FSM for your car has an exploded view of where all the vacuum lines from the IM go.

Here's a view of what you're working with under there (minus the PCV branch);

https://i.ibb.co/1MPL3g8/under-IM.jpg (https://ibb.co/MftsbvM)

Do you have an EGR delete? A lot of the time, when someone does the EGR blockoff plate they don't take the time to get all of the old gasket material off of there and the blockoff plate barely seals. Could be a culprit.

[DiscountPirate]

Typically a vac leak would cause a high and irregular idle so possibly a huge vac leak. I assume you cleaned the aicv and adjusted that and confirmed it's working? Only other random thing I can think of is maybe if TB flap has too much tension and is slightly open all the time.

[K4RR]

Inside the iac regulator there is a spring and sometimes it can come unhooked or break and cause a high idle like you describe. You can take it apart by removing the screws and look. https://www.efisolutions.com.au/assets/full/204-086.jpg?20181219115849

[kyral]

doesn't a vacuum leak usually lead to a crappy idle?
I would think thered need to be an extra fuel problem in conjunction with the vacuum leak to create a high idle.

have you tried adjusting the iacv? not just rplacing it.

[NukeKS14]

doesn't a vacuum leak usually lead to a crappy idle?
I would think thered need to be an extra fuel problem in conjunction with the vacuum leak to create a high idle.

have you tried adjusting the iacv? not just rplacing it.

Disconnect the vacuum line at your brake booster while your engine is at idle and see how it responds. It's a good theory-to-practice test as you can connect it right back up once you've confirmed what we're saying. This creates a large vacuum leak so you'll see engine speed raise quite a lot.

FYI the ECM uses a 2D table utilizing load% and RPM as axis. It measures your load by airflow through the MAF (density compensated by temperature) and RPM off of the CAS. You will cause RPM to go up and load to stay the same(because the air leak you're creating bypasses the MAF) but, yes, it will add more fuel based on the new VE table conditions it is now seeing. It would be lean-ish but that's beside the point; the motor will rev up.

A quick dummy-check on whether you've got a vacuum leak or not is to pinch off the line feeding your IACV/AACV (the 5/8" line going from the intake to below where the upper radiator hose connects.) Under normal conditions (without a vacuum leak) the engine will stall out and die. If there IS a vacuum leak from something other than the IACV/AACV, then the engine speed will lower but it'll still be able to idle.

Back to the main topic, assuming OP has solved the problem as this is over 2 months old with no follow-up from them.