The solenoid (an electro-magnet) that goes around the IPR should ohm out between 10.2 and 10.6 ohms and hold steady. That's the range on some I have. Just loosen the nut, remove the spacer and pull it off the IPR. If it has any kind of intermittent short or open the needle valve inside the IPR will not move properly and/or default to open dumpimg the HPO into the front cover.

Here's a PDF for cleaning the IPR.