Hi Folks

1998 Accord, 4 cylinder, automatic trans. I've been living with a goofy idle for a couple years (I'm original owner, 375000 miles). The vehicle is well maintained and after a recent tune up I decided to replace the IAC, as the idle was still funny. Some days it'd be fine, others it would drop low etc. The only DTC code with this has been p0301. I purchased a Standard Motors unit from eBay. After installing the new unit and firing up car, idle was extremely rough and car threw code p1519 for first time.

Following the Honda trouble shooting, circuit showed battery voltage on middle terminal with ignition on, but no continuity between terminal one and ground. The book says to repair open between IAC and g101, located on driver's side on manifold. How is this done? Do I have to tear apart the harness, or could it be a problem at the connector? Any help is appreciated, I'm not very savvy with electrical issues! Thanks in advance.

 

I may have mistaken terminals 1 for 3...the pic shows an alignment tab I assumed was the top but the tab is on bottom of connector. Any who, I have continuity at terminal one (blk wire). I'm now trying to figure out which connector on pcm is 'B' 25p. Is this located below the radio etc??

 

The PCM is located under the center of the dash. Connector B is the Gray 25P connector (located between A and C). Pin 23 has the IAC Blk/Blu wire.

 

You should never replace a part without verifying the part is bad. I've seen where aftermarket parts can be bad out of the box.

Try reinstalling the original IAC to see if the CEL goes away.

To determine the original problem, I'd recommend a scanner that can read some basic live data. Look at sensor data to see if it looks normal, like coolant temperature, throttle position % open, etc. Also look at the fuel trims when the engine is idling. The long + short term fuel trim should be close to zero when you add them together.

 

Thanks Redbull-1, I was in the ballpark with that B connector but wasn't 100% certain. I tried replacing with original IAC and reset the DTC but the rough idle was still present and the code returned. I use a BlueDriver scanner and app on my phone, which has live scanning and data logging capabilities. I've never seen anything out of the ordinary in the data. The BlueDriver suggested replacement of the IAC after tune up items were replaced.(plugs, wires etc.) I'll continue trouble shooting tomorrow. I'm surprised how adding a part I thought would fix a rough idle has made it dramatically worse. The car is not drivable as is and readily stalls.

 

Testing indicates an open between IAC valve and B23 in the pcm. Now the fun begins.

EDIT: No open...I mixed terminal one for three again on IAC connector.

 

Okay, the last step of trouble shooting the IAC circuit, you reconnect the pigtail to IAC, turn ignition switch on and measure for battery voltage at 23B. I measured 11.58 volts, the battery was at 12.28. Is this considered battery voltage? Because if not you replace IAC with new unit. If this can be considered battery voltage it says to replace the ecm/pcm. I have a hunch I need a new computer since I already tried the new IAC which caused worse symptoms than before I began this repair.

 

I want to update this thread. I ordered a remand pcm but haven't received it so the car's been sitting for 10 days (eBay seller has provided tracking but hasn't shipped it!). I went to start it. It cranked for a while and only fired after putting the throttle to the floor. I had cleared the previous codes and it was idling remarkably well but with a distinct misfire. I let it warm up until it threw some codes. The car stumbles badly on tip in throttle, like you have to pump the throttle to get it to rev and will stall without some throttle manipulation. The prior p1519 didn't resurface, the current codes:
P1382 CMP sensor A no signal
P0301
P0302
P0300
All the troubleshooting for the P1382 checks out fine, except it wants me to try a known good pcm. I replaced the distributor with an oem one less than a year ago. I pulled the plugs, which by the way were very fouled, black and sooty, for a compression test:
1: 175
2: 210
3: 215
4: 215

The saga continues!! It sounds like I'll need the pcm synced to the car to work with the immobilizer...

 

So after getting a remand ecm flashed to my car with no success, I tried another IAC but this time opted for the oem Honda unit instead (Amazon $248!) and that solved this long drawn out saga. In retrospect, the original IAC must have been compromising my idle for a LONG time as the quality of it had been funky for a number of years. The irony being the car only ever through the p1519, iac code, after installing the Standard Motors Product iac from eBay! Any who, I hope this thread will help anyone who might experience the same thing and save them some time.