Adjusting idle screw doesn't change idle at all

[gnozahs]

When I go to turn the screw to adjust the idle, the idle does not change at all. Currently it feels like it's turned all the way clockwise so I turned it a counterclockwise and the idle did not change at all. I warmed up the car, turned it off, disconnected the TPS, turned on the car, revved it to 2k for a while, adjusted the idle screw and nothing happened.

Idle currently sits at 1500RPM and when you rev it, it'll bounce from 1500-2000 a couple times and then stabilizes out at 1500RPM.

Motor is a KA24de 5 speed.

Also, it feels like the idle adjustment screw doesn't spin that much. It probably goes half to 3/4 turn in each direction and then stops. I didn't want to force it anymore and lead to breaking or stripping it. Is it supposed to have more adjustment than that? The screw looks like it sits in pretty deep already.

[pacotaco345]

Check your timing and check for vacuum leaks, if your car has a vac leak it doesn't matter how "closed" the iacv screw is, its still gonna leak too much air to ever idle correctly.

[TougeSR20Kid]

Check your timing and check for vacuum leaks, if your car has a vac leak it doesn't matter how "closed" the iacv screw is, its still gonna leak too much air to ever idle correctly.

+1 also may want to clean the throttle body as built up shiza can cause the throttle to not close properly. But mainly check for a vacuum leak as this will cause a high idle

[Def]

Sounds like a vacuum leak, but normally the screw doesn't adjust the idle. The ECU has a table in it which changes the target idle speed vs. coolant temperature. The idle screw is to adjust the response of the idle valve, or in rare cases trim the idle air out so the ECU can get the idle speed to the correct RPM.

The screw acts as a constant flow path, and the idle valve pulses to add additional flow. Each one cannot provide enough flow for the idle by itself, so they both work together.

[gnozahs]

Check your timing and check for vacuum leaks, if your car has a vac leak it doesn't matter how "closed" the iacv screw is, its still gonna leak too much air to ever idle correctly.

Alright so how do I go about checking for vacuum leaks? I can visually check all the tubing but I can't tell if it's good or leaking. Is there a write up on how to go about it?

[waxball88]

Pressurize the system or you can use smoke to see them

[gnozahs]

Okay so I tried spraying carb cleaner onto all the vacuum lines and vacuum connections that I could possibly see and the idle did not change at all.

[gnozahs]

Just checked the timing and it was at around 5 degrees. I rotated the distributor to the max and could only get it to 15 degrees. Idle of course went up and is at 2000 RPM now and bounces from 2300-2000 a couple times before evening out at 2000 when you rev it. I've also checked the distributor timing and it looked good. Rotor was in the 930 oclock range and cylinder 1 lined up to it with the crank pulley at TDC.

[gnozahs]

Update: So I found out my 5 speed swap still has the original automatic ECU in it. Would this be the problem for my idle to be so high?

[zerodameaon]

Did you pull the TPS connector when you timed your car? Also ECU has nothing to do with it. I still have my Auto ECU and I can adjust my idle up and down all I want.

Try these steps. The same steps as any other walk thru now with pictures!

http://zilvia.net/f/s-chassis/395413-idle-adjust-procedures-ka24de-240sx-pictures.html

Also clean your IAC and check your throttle as stated above. Somehow the guy who owned my car before me bent the throttle bar so it wouldn't open all the way(could also cause it to not close).

[ShadowMan]

Try removing the idle screw completely, and applying some oil to the O-ring. Spray carb/brake cleaner or starter fluid in the idle screw hole and clean that out with a q-tip or tooth brush or whatever. Re-insert the screw all the way in then adjust from there and it should twist in/out quite a bit smoother than before. I was about to post my idle problems, then tried that and its signifigantly better now. Maybe it'll work like it did for me. My idle is not completely fixed but it is very close to being spot on. I have an s13 blacktop, but I don't think that matters. An idle screw is n idle screw. let us know how that works out.