ive searched this problem before posting this and nothen helped. i recently replaced my upper o2 becuase the heater part was inop, and that fixed it, but as soon as after i cleared the code, p0505 came up, idle is super low, @ around 200 rpms, iac is working fine and i have no vac leaks, i took negative off and let sit, after a 1/2 an hour, retryed it, and was fine untill i reved the **** out of it, at that same time the thermostat kicked open.

i shut the car off and restarted, now with cel still on without touching the throttle, my tps was at 9.5 % and map was at 22 kpa @ 1100 rpms..... if this helps.

ive asked my fellow honda mechanic buddy and has never heard of this problem with a properly working iac and o2.

thanks
matt

 

also, the car has been sitting for 2 months. with my otc scantool, when i checked all the monitors for the evap and catalysts read INC. was also told that i may need to drive it to set the map, as like on early 90 year fords.?

 

what year is your car?

 

Here is some info from that i pulled off alldata at my shop. It has the description of the DTC and I also have posted a trouble tree to help the diagnostic. Hope this helps. The info is for a 97 civic ex 4 door, but the engine and trouble codes are the same.

[P0505] The scan tool indicates Diagnostic Trouble Code (DTC) P0505: Idle control system malfunction.
NOTE: If DTC P1508 or P1509 is stored at the same time as DTC P0505, troubleshoot DTC P1508 or P1509 first, then recheck for DTC P0505.

Possible Cause

IAC valve mechanical malfunction
Throttle body clogged port, improper adjustment
Intake manifold gasket leakage
Intake air hose loose leakage
Vacuum leak
ECT sensor incorrect output

Here is the trouble tree.

 

thanks for the trouble tree, will deff try her out. was hopeing someone would post one. will let ya know what the problem is tomarrow.

thnaks
matt

 

will say though that the p0505 code says *pending* donot know if that means anything

 

pending just means that it the code has not matured to the point of turning on the MIL (Check engine light) yet. The computer is looking for it to fail again before it throws the MIL on. Seeing as your car is a 98 I believe, it is OBDII so it is working on basic logic. example: I am going to send a message to this component this drive cycle and if it doesn't respond in time or is with parameters, I will ping it again. If it fails the second time I will turn on the MIL for a open/short or emissions reason over 1.5% the FTP standards. (Federal Test Procedure)." OBDI only worked on opens and shorts.
~David

 

but your thinkin it is the iac. what are the chances being cts, makes sence but the temp is ok. and what about the evap purge, that runs on vac too.

 

if temp is okay then cts is fine. evap purge only works at freeway speeds.

 

Even though the IACV is electronically functioning, have you verified it's nice and clean? It may not be moving like it should be and that would cause your low idle problem.

 

A pending code would show up on an OBDII scan but would not cause the CEL to remain on. So I don't understand why P0505 is pending when the CEL is on steady. Can you clarify?

When the IACV is unplugged, does the idle speed increase?

Are you sure the IACV port from throttle body to the IM is not clogged?

Did you troubleshoot the ECT sensor and its wires?