Sometimes an engine will seem to idle more smoothly when there is no load simply because the flywheel is carrying the cylinders across anything that is misfiring. Check the compression first. If all cylinders are within a couple PSI of each other you probably don't have any bad valves. If you haven't replaced the plugs, distributor, rotor and wires for a while, that seems like a good next place. If it still isn't cleared up checked the injectors for anything that might be partially plugged.
sounds like a bad head gasket
Added info to question: Vacuum also coincidently went from steady 20psi to 15psi/knock - small backfire/miss on acceleration from idle. Knock is steady at idle.
the fuse panel is clearly "WARNED" and "LABELED" in the engine compartment on the right hand side, really impossible to miss.
You are just starting it and putting in gear from an Idle? Rev it up does it miss? The dist is probly 180 degrees out, pull dist and make the rotor point in opposite direction
Proberly a miss fire in one of the cylinders.
Miss out? I am not sure what you mean. If you are saying that it wont go into gear, or its throwing it out of gear, the transmission is going (A gear has shattered). If it is "missing" or miss-firing, it could be your plugs and wires. Those are the most common solutions to this.
A exhaust manifold that is warped, cracked, or missing a gasket will make a sound like a engine miss. I usually look for soot near the suspected area to tell for sure.
Check your vacum lines. The rubber and plastic hoses under the hood. If one is loose and leaking, it will cause a miss. If it only does it at idle, it will probably be a small line or just loose. that's the first and cheapest thing to do.
On the bottom of the radiator usually on the passenger side. **Correction** Sorry! It's not necessarily on the passenger side, don't know why I said that. It's on the driver's side for my caravan so it really depends I guess. Just take a look at each side of the radiator at the bottom, you can't miss it.
Unlikely. A faulty IAC will give you poor, erratic idle speed.
miss alignment of tires
I blown head gasket can cause an engine miss which one cause a rough idle.