Originally Posted by Shadow1198

I know this has been addressed many times here before but I wanted to make a new post that addressed all of these problems as a result of a single part rather then many different malfunctioning parts. All of these problems can be caused by lots of different things BUT, there is one thing in particular that can cause all of these problems by itself. The part is the Idle Air Control Valve (IACV).

Basically, over time carbon deposits can build up on the valve and cause it to stick. If it sticks, it can cause the TPS sensor to not work properly which can cause the snowball effect to begin (leading to more and more problems). Here are the following problems I had and my diagnosis of them (you'll begin to see the "snowball" effect this little b@stard valve can cause!):

-Lopy idle (a result of misfiring)
-Running extremely rich in low-end and at idle (real-time diag on ECU)
-Running lean in the top-end and throughout most of the rpm band (real-time diag on ECU)
-Misfiring (a result of running so rich at idle/low-rpm)
-Missing/bogging low-end (running too rich will bogg the engine down)
-Missing/bogging high-end (running lean can have the same effect as running too rich)

I've been having ALL of the afformentioned problems. Basically, my whole entire power band seemed to be lacking. It all boiled down to the IACV. My IACV was clogged with carbon deposits, which in turn caused the valve to stick. Because the valve was stuck, this can cause air to be entering through it when it is not supposed to. A direct result of this is that the TPS sensor will not function properly, and replacing/adjusting the TPS will have no effect. With the valve stuck, a direct result is also to cause the engine to run rich with the throttle closed and low-rpm, as well as running lean through most of the powerband. Running so rich and lean at the same time can also cause your Maxima to misfire a lot and have a lopy idle. With the TPS not functioning properly the throttle doesn't quite act right in that it takes awhile for the rpm to fall. This can be seen in engine braking, revving with the clutch pedal in or in neutral, etc. Basically, after 2yrs of diagnosing these d@mn ECCS gremlins I found out MY problem. All I did to fix all of my problems was remove the IACV and spray carb cleaner through it to clean all of the deposits off. After 2yrs of replacing parts and dealing with this crap, I solved my problem in 5min (the parts I replaced helped of course)! One thing I should state is that out of all the parts I replaced, none of them really had much of any effect on the problems I was having. Cleaning the IACV is the only thing that has drastically changed/eliminated these problems. So far, everything is working great but I haven't put any serious mileage on my car since fixing this. I'm going to fill up with gas today and see how my mileage will be affected. I'll respond later next week to let people know if cleaning the IACV really has helped me that much with performance, gas mileage, etc. I replaced the following trying to fix all this crap:

-spark plugs
-wires
-dist cap
-rotor
-air filter
-fuel filter
-pcv valve
-ignition coil
-MAF
-cat
-o2 sensor
-tps sensor


Now, this IACV valve is really tricky because I have seen lots of other posts where people with similar problems have replaced the TPS, EGR, FPR, etc and it doesn't help plus the problems continue. Let me tell you this, CHECK THE IACV!!! I never thought that simple little valve could cause all the problems I was having but the fact is, it was pretty much the single reason I was having ALL of those problems! There are, of course, many other things that can cause these problems. So, cleaning the IACV might not work for everyone but, it is definitely something you should at least try.