This is the riddle. Your 1986 na 300zx 5 speed when purchased contained factory air intake system. You also suspect that there is an exhaust leak or something along those lines, but you don't notice a lack of power. You replace the factory air intake system with a K&N aircharger cone 9". The car then has idling problems. It also has cold start problems. It does start when it's cold, and doesn't actually die when it's warm and idling. It just has problems in the two areas. You put the original factory air intake system back in place after a month, removing the K&N cone. The car no longer has idling problems. It does however have a SLIGHT missing/choking sound, but does not effect power of acceleration to a startling noticable point. SO.....here's my opinion, the K&N gives the intake more air than it can handle due to the "problem". What is the "problem?"
Ok, sorry for the riddle structured question, but this definitly has me confused, master mind 300zx owners out there, this is the true test!

 

you didn't disturb the plumbing from the airflow meter/mass air sensor to the manifold putting on the K&N, and then tightened it up when you went back did you?

 

I would have to say no. This is the 2nd time I've changed it back. Think of it this way. When you put on a K&N cone it let's the intake take in more air right? Well what happens when you hav a leak? The intake takes in more air. I think that there is a limit on how much air the intake can take in before it starts having idling problems. Surely there are others out there besides myself that have had troubles with the K&N air cone.

 

Most idle problems are related to a faulty or mal-adjusted throttle position sensor or more air getting into the engine than is supposed to happen.

Since your AFM is measuring the amount of air coming into the engine at all times, and since the stock air box is somewhat restrictive, the AFM doesn't see as much air. And the ECU doesn't have to try to compensate for it.

Since the K&N allows more air, and since something isn't aligned properly, more air is getting in.

First: check to make sure TPS is adjusted properly. See the attached image.

Second: check the throttle body itself to make sure it's closing all the way.

Third: check the start looking into the auxilary air devices around the intake plenum. aac, egr, idle-up, air regulator, etc. one or more of them could be bad.

It never hurts to run codes on the ECU ya know.

 

ok, heres the deal. Codes are as followed, 2 red 3 green then its 3 red 1 green. Thats all the codes I can get it to give. I know that for some reason my defrost doesn't work, acually none of the functions that have to do with the blower motor fan works. I have absolutely no air movement in my car. If I replace the fuse then it works but will just melt the fuse or burn it out after a few uses.

 

how do you adjust the idle switch?

 

nevermind the throttle adjustment question, I didn't think my haynes manual had the adjustment procedures in it. It does though.

 

Look, I have had the same problem as you.
I tested my computer and got the same result. I then tested the T.V.S.(throttle valve switch) and the M.A.F.(air meter).
Upon testing I discovered both parts were good, this meant only one thing; MY COMPUTER WENT BAD!!!!!!
I hope you do not encounter the same problem, but if your
M.A.F. & T.V.S. tested good you will need to replace the E.C.C.M.

GOOD LUCK!!