Engine idle for this model car is supposed to be 700 rpm plus or minus 50 rpm. When I first purchased this car, I noticed the engine idle speed was too high. It was idling around 1400 rpm. I made some adjustments, replaced the Air Regulator, and had a new gasket put in for the Idle Air Control Valve (IACV).

The most I have been able to reduce the idle speed is down to 1000-1100 rpm. I haven't been able to get it to normal idle speed. I have made every adjustment and performed every diagnostic procedure according to the FSM. When that failed, I tried swapping the ECU. That didn't work. Then I tried swapping the IACV from a car with a known working IACV. That didn't work either.

I have exhausted all of my options from the FSM and from what I know about working on these cars? I would appreciate any further advice or information from someone who has a lot of experience with engine performance on these cars.

Installing a new OEM IACV should solve the problem. Stay away from aftermarket IACVs--they are notorious for causing idle problems. Clean the passages while you are at it.

Thanks TX, but the M/T IACV is NLA. :( The 300ZX is a dying breed. Searched high and low; can't locate one from any auto parts supplier i.e. ROCK AUTO, NAPA or CARQUEST. Sometimes I see them on eBay, but I'm cautious about buying a used one from eBay or the junkyard. The only one that may be available is for the A/T and I'm not sure that would work. I'll try cleaning the passages tomorrow since I have it off the intake manifold.

One thing I noticed is the IACV from the 84 had a spring inside it, and the one I swapped off the 85 did not. Obviously it didn't make a difference though since the idle speed didn't change.

Update

I cleaned and lubricated the throttle plate stop and IACV. There was a lot of tar, grease and oil deposits in there. Reinstalled IACV components and ran engine long enough for ECU to relearn the idle.

It worked perfectly! The engine is now running between 750-800 rpm. I don't need a new IACV after all. Thanks Tx, you really are a hero!

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