The soleniod is held on by that sheet metal nut at the end of the IPR. That nut is likely not tightened down enough. Make sure it is good and snug but not over tight as its a thin sheet metal nut. If it comes off the engine will idle like crap, sputter on take off and die off and on near or at idle. If it keeps coming loose replace the nut and maybe add some purple loctite to the threads.
When you pull one while the HPOP is on the engine you take that nut off then the sleeve and solenoid side off. Then you can use a 29mm Deep sock to get the main body unscrewed from the HPOP. The top nut is 3/4" IIRC.