Outer Limits 4x4 Board

After a run out yesterday my 40 no longer idles? As soon as you take your foot off the gas it stalls. If you give it a bit of gas all is well and it drives no problem as long as you don't put the clutch in with no gas. A bit of hand throttle means it can be driven. I did some research which led me to test the vacuum lines which are all 14" at very fast idle - using hand throttle. This seemed OK so I next checked the PCV. Didn't really know how to test that but I took it off and blew through it and it seemed OK. I gave it a good spraying with carby cleaner just in case. Next I looked at the the idle solenoid. I took it out and and placed the body of the valve against the rocker cover to earth it with the key in the on position and it makes a nice reassuring click. I couldn't see anything happening so I disconnected it and ran it across the batery so I could take a closer look and if you look very closely through the brass holes something seems to move but it's hard to tell what. I was expecting a plunger to retract or something that would be conclusive. What is it supposed to do? If it was working properly would there be an obvious movement or something? There's definately nothing obvious moving dispite the nice click sound.

I suspect it might be the solenoid despite the reassuring click but I'm not sure if you're not supposed to be able to see the plunger retract?

If the solenoid is OK what is everyone's next guess?

The truck is a 1984 FJ40 with 2f. It runs on dual fuel and it's running sweet on LPG. It's running perfect on petrol apart from there being no idle. It's not almost idling either, when you take your foot off the gas it's as if you've turned the key off. It doesn't take a second or two it just dies. It's weird because it was fine yesterday morning. Some of tracks I did were pretty bumpy so that could have shaken something maybe?

Any advice will be very gratefully received. BTW I'm not much of a mechanic so please keep it simple:)

Thanks, Phil