Idle Control System Failure [14-2 (P0505)]

[princxixor]

The check engine light has come on twice now on my '98. Same code both times; 14-2 (P0505). I had Foreign Affair (FA) pull the code for me and they say it refers to "Idle Control System Failure". The FAQ says it's a "IAC System Malfunction". However, FA isn't sure what may be the problem, though the throttle body was mentioned. They also think it is ok "as is" if the light doesn't come back. However, I'm concerned because the car does exhibit other symptoms with idle:

1) car idles pretty low at stop (approx. 500rpm) when warm.
2) tendency for revs to dip very low on clutch engagement to <500rpm and then jump back up to around 500.
3) car has actually stalled twice on clutch engagement, but not recently*.

* recently meaning since the check engine light problem started. The first stall happened at NSXPO 03. At the time, I asked Mark Basch and he (also) thought it was carbon buildup on the throttle body. It happened once more, maybe a month later, but then never again.

Now that it is back, I'd like to fix this. Car has ~65k on it now, the first time this happened was shortly after the 60k turnup I did at about 58k.

Anybody have a guess as to what might be causing this?

TIA!
~eric

 

[Briank]

The ECU uses the idle control valve to control the idle speed. If your idle speed is 500 then the EACV AKA (idle control valve) is not working or the passages in the throttle body for it are clogged.

 

[hlweyl]

Make sure you are reading the tach correctly. I made the same error before. Notice the lines on the tach, first line is 0, second line is 500 rpm, then 600, 700....

So if you are idling at 500 rpm, then your needle would be at the first line. If that is the case, then yes, that is way too low. The procedure for resetting the idle is in the procedure manual: http://www.nsxprime.com/FAQ/Referen...1991_svcman.htm

I had the same problem, here is my post from a while back. http://www.nsxprime.com/forums/showthread.php?t=34745 A half turn on the idle screw and reset the idle did it for me.

good luck

 

[D'Ecosse]

Might still be a good idea to clean the TB

 

[Larry Bastanza]

Might still be a good idea to clean the TB

What he said for sure.

Make sure you disconnect the four small hoses at the top of the throttle body assembly and quirt some gumout into each passage. This is more critical on ODBII cars since the idle system is different and is dependent on one of these passages.

HTH,
LarryB

 

[NSX-Racer]

The procedure for resetting the idle is in the procedure manual: http://www.nsxprime.com/FAQ/Referen...1991_svcman.htm

Attention: As you have a '98 model like mine you have to watch some different places of the screws. Procedure for TBW cars was described
here

 

[princxixor]

Ok, so I've double checked my numbers. I did state them a bit low as hlweyl suggested, but I don't think I'm way off. Also, I think some days are better than others. Today anyway, I'm getting:

* idle between 650 and 700.
* dips on clutch engagement usually to about 500 (but I have seen it go lower lower).

Thanks to all for their replies. I think I will try cleaning the TB first, and then if my baby still idles low, I'll try resetting the idle.

Cheers! :smile:

 

[suntaelee]

Ok, so I've double checked my numbers. I did state them a bit low as hlweyl suggested, but I don't think I'm way off. Also, I think some days are better than others. Today anyway, I'm getting:

* idle between 650 and 700.
* dips on clutch engagement usually to about 500 (but I have seen it go lower lower).

Thanks to all for their replies. I think I will try cleaning the TB first, and then if my baby still idles low, I'll try resetting the idle.

Cheers! :smile:

has anyone solved this problem? i have the exact same problem. do i need a new iac valve?