High Idle Problem

[dhkemp91]

Ever since i got the Z it has idled high. Its a '94 NA Manual transmission. Im beginning to slowly replace all the corroded connector harness all throught the engine. I just removed and cleaned the IACV. I removed the Air regulater and it looked good. I scraped all the connectors clean and I also bought and put on new harnesses for the 2 IACV connectors and the harness for the air regulator. I reinstalled everything and started with the adjustment screw all the way out. started the car and it was around 1500 after warming up. i started to screw in the adjustment screw and i got it down to about 900-1000 with the screw fully in. then, today i unplugged the negative battery for 30 minutes to let it reset the ecu. Hooked the battery back up and then I checked and adjusted the tps. It was around .425V fully closed and with throttle fully open it was like .37V which is low i think. The connector coming out of the bottom has all clean pins and clean connector, but the connector on the front of the tps has all corroded pins and the conecctor is even missing one of the metal inserts. (im wondering if this is my problem). I unscrewed the adjsuter screw again. I started the car and it went up to just under 2500 rpms at idle. So i unplugged the AAC connector on the AICV and it dropped to about 1500. i Screwed the adjuster screw in all the way and that got it down to about 700-750. but the second i plugged the AAC connector back in it shot up to around 1900. Before i started messing with anything it was around 1000-1100. Any ideas on what the problem is? Bad tps? Bad tps connector?? please Help!

This morning the idle is now at or Above 2000. When I turned the air on it went up to about 2250 which means the iacv solenoids are working right I think. Any suggestions would be very helpful! I'm running out of things to try. Thanks!

[MrVetis]

I have same ordeal with my Z . I to have checked for air leaks an bad connectors. I can turn screw completely in & it seams as if the computer just keeps it running where it was after a few seconds. But I have a timing issue I need to fine tune also tho..

[scsuh]

also having similar issue. Just had three injectors, pcv hoses, and bad connector replaced. car is now idling at 1500-1800rpm. gonna take it to an independent nissan shop to have it looked at but was wondering what I should have the mechanic look at in particular. thanks much.

[dhkemp91]

I would say have him look at the Idle Air Control Valve and connectors, and also at your Throttle Position Switch.

[thezman86]

A vacuum leak can cause this probably you can spray the manifold with something nonflamable while the motor is running and see of it changes

[dhkemp91]

Well I think I got the high idle fixed. I adjusted it at the throttle. The stopper screws on both sides. I got the idle down and still have some adjustment room in the IACV screw. Do you know what it should idle at when at temp with the heat or a/c on? Having the air on causes a pretty big increase in the idle. I just ordered a boost leak tester so Ill be able to find out for sure if I have any leaks.

[DarkstarNovermber]

I'm having the same problem. I also notice when driving the RPMs will hang just under 2K when decelerating or pushing in the clutch.

When I turn on the AC the idle rises slightly then quickly returns to its previous position.

Here's a write up to help.
http://www.mdsmarthome.com/z/Z%20Tech/Z ... 20Idle.pdf

[datdude407]

TPS sensor. get a multimeter and check it out. Happened to me when i pulled my plenum the 2nd time

[jschrauwen]

Improperly set (read sync'd) throttlebodies can give you poor idle conditions. I've done a How-To on sync'ing them on 3ZC and tt.net.

[es.biggs]

Vacuum leaks can cause it and they are really common - the best way to find them is to smoke test it. Unfortunately that requires special tools...spraying TB cleaner on the manifold and vacuum lines etc can help you find one but it's not really accurate. Worth a shot though.

[dhkemp91]

I actually got a boost leak tester and pressurized the system to around 4 psi and I have a couple leaks. One is behind the engine basically in the middle im leaning towards the egr. Another area is very faint not sounds like its around the passenger side intake pipe at the front. I am planning on doing a plenum pull and complete injector replacement as well as egr delete. Think that would solve most of my problem?

[es.biggs]

If you replace all of your vacuum hoses it probably would do the trick

[vg1134]

Engine temp sensor gives you high idle also. Check the FSM manual it will give you the values it should be at on certain temperatures.