Fluctuating RPMs and code P0505

WESLOSNIPES1995

MEMBER
1999 HONDA CIVIC
1.6L
4 CYL
2WD
MANUAL
186,000 MILES

Rebuilt the d16y8 motor and replaced the IAC motor and I threw it away. I'm getting pumped code p0505 and having a idle issue where after it warms up it will fluctuate between 1,500 and 2,000 RPM's. I have 0 resistance between the PCM or whatever Honda calls it, and to the IAC. I have unplugged the IAC sensor adjusted the ignition timing to spec and adjusted the idle air valve on the throttle body so it sits at 620 RPM's at idle I plug the IAC back in and the motor going right back to fluctuating idle, performed a smoke test and no vacuum leaks found and have the Honda jumper wire they ask for to do the adjustment. I'm looking to see if I'm doing the adjustment wrong or missing a step or if or if new IAC sensor is bad right from the box.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

It does sound like you have a faulty valve after that but I attached some info on it and how to adjust the idle speed. Let's make sure that is correct since you mentioned it and then check for vacuum leaks using the method shown in this guide:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Basically use brake fluid around the engine while it is running as it is a little more effective then smoke. The smoke works well on the intake and some attached lines but when the engine is running we may have some larger leaks that don't show up with the smoke.

Worst case, let's swap the IAC for a new one and see what happens. Let us know what you find. Thanks

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