99 EX: CEL code P1509 (IACV)

99civicd16y8

New Member
hey guys got a 99 civic ex stock d16y8 automatic. i have a code with p1509 idle air circuit malfunction, i replaced the idle air control valve and no luck, replaced the spark plugs, wires, cap and rotor and still no luck it idles low when in gear especialy with the a/c on. tried adjusting the screw on the throttle body and no luck. the cel light will not erase if i erase it with a scan tool just pops back on. any ideas or anybody else have had this problem
 

RonJ

Banned
Unplug the IACV connector, turn the key to ON(II), and then measure voltage to body ground from the middle terminal of the 3P wire harness side connector. Do you measure battery voltage?
 


99civicd16y8

New Member
ok i checked it out yea i get battery voltage from the middle wire. i also decided to check my battery and alternator battery voltage is 12.64volts when the car is on 14.20volts when i turn the a/c on it drops too 13.07volts, bad altenator?
 


1993DX

New Member
Is a low idle the only issue.. Any loss of power or stumbling at part throttle?

Check your vacuum lines / hoses too.
 

99civicd16y8

New Member
it stumbles while accelerating, but i was playing around and when i disconnect the ect it runs alot better than with it connected lol. so ima replace it with a new one see how that goes
 

MotoRyan

New Member
HELP Same Problem

Yes did you figure it out? Would you post or email or PM me?

1999 Civic DX 1.8 SOHC Automatic
Car wash in the morning. Ten minutes later, CEL and low low idle. Car only runs with my foot on the gas the whole time. Down to Pep Boys to get the code read. Only code P1509
Take the TB off and disassemble the IACV and clean it. Check the connectors (no corrosion or any signs of loose wires). No luck same problems (rough idle, CEL).
Make the DIY mistake of dropping 180$ for a new IACV. Replaced and started car, same problems.

I originally suspected the wire harness from the IACV to the PCM. I DO NOT WANT TO ADMIT THAT IS A PROBLEM WITH THE WIRING. May be the case.

PLEASE anyone figure this problem out. ??!!
 
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