Yes Fred. The IAPV is the Injection Actuation Pressure Valve and you have the operation correct. It has been a bit of a problem for many 3126B engine owners. I have replaced 4 on my unit in ~145,000 miles. When it fails, either the engine will be very hard to start or won't start at all or if the engine is running, it will go into engine protection mode and limit the speed to ~45 MPH. When this happens, it will typically set codes 15 and 39. Replacing the valve requires a 1 1/8 wrench and about 15 minutes of your time... and about $200 of your dollars if you use a CAT valve.
I will be testing my cleaned valve in a few days as I need to make a quick trip to Tucson but will have a bit of time to get back so I intend to install one of my cleaned valves while there and see how it performs on the way back. I'll report when I get bacx.
Steve
