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I have a 1999 Honda Civic LX with D16Y7 engine. I threw a P1505 a few weeks ago, cleaned the IACV and it went away for a few days, then came back. So I replaced the IACV and the code went away. But days later I get a P1509. I've tried my hand and some electrical test, I found a tested ECU and tried it, but nothing. I'm getting voltage at the center pin on my three pin connector for the IACV. I've been trying some of the test out of the service manual to check for a wire problem, but I'm having a hard time understanding the steps when it comes to what wire to probe on the ECU connectors p25 and p32 according to the service manual, but my connectors do not look like the one in the book. Therefore I'm not sure which wires to probe there for the test. I've also cleaned three ground wires uber the hood. I'll attach photos that may help explain some things.

Service Manual for testing P1509 on a D16Y7


Photo of what my p25 connector looks like, seems different that the diagram in the book for a p25

 
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Did more research and tested everything by the service manual I've linked in the post. I reset the code and it comes back immediately without the car running. I did not pick up any voltage between B2 and B10 to body ground.

B6 and B15 have battery voltage

New IACV resistance falls between 16 - 28 ohms

With the ignition switch on I get batter voltage at the number 2 connector on my 3 pin IACV connector

I tested continuity from IACV 3 pin connector to where they connect on the ECU. Everything checked out.

I found no continuity from body ground to B6 and B15

Absolutely stumped here. Like I said in the post the IACV and ECU have been replaced. Any help would be MUCH appreciated. I've never had to take a car to the shop, so I'm dying inside a little currently. Lol

 
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Several years later than OP but may be helpful to others.
I have a 1997 Civic mt D16Y7. I had it for several years without any problems. Last summer it began to stall when idling -- like at red lights. Replaced the battery. Continued to stall. I replaced the ECU with a used one. Ran good for a while. The problem returned. I got a code scanner and threw P0420 -- catalytic converter. I found a couple of broken wires (one to the VSS; the other to the tachometer in the ecu) and reconnected them. No CEL. The problem resumed. I followed the tip from "conspiracy90" at "https://www.civicforums.com/forums/36-mechanical-problems-vehicle-issues-fix-forum/23983-new-findings-stalling-problem-3.html#post678225" and, apparently, it resets the ecu.
Works like a charm. Didn't do this when I replaced the last ECU.