NF Mod/Nissan Master Tech
Joined: Jan 2006
Location: Prospect, VA
The IACV-AAC valve controls the fast idle and maintains base idle by compensating for loads placed on the engine, ie P/S, A/C, etc. It is commanded by the ECM. For it to work properly, base idle setting must be correct. This is usually done by warming up the engine to normal operating temperature (run engine at 2000RPM for 2 mins) and shutting it off. Unplug the TPS and restart. The IACV-AAC valve and TPS are now in a "fixed" position and the idle speed is now the base idle. Adjust the screw on the IACV-AACV until the engine will idle (if necessary...lower, if too high) and adjust the ignition timing to spec (rev the engine 2000-3000RPM a few times with all loads and accessories off before doing this). Timing spec is 8 degrees BTDC +/- 2 degrees. Adjust the idle.
AT: 725 +/-50 RPM
MT: 625 +/-50 RPM
Turn off engine and reconnect TPS.
If you still have idle problems and you've done your basic checks (confirmed no vacuum leaks, ignition system OK, etc.), you could have a faulty IACV-AAC valve and/or a bad diode. Refer Nissan technical service bulletin NTB97-008.