84 Urvan. Totally loses power. Very little response on accelarati

need make model year engine type or you will not get answers
post again and ask a question with all that information included

timing may be off, the belt for the engine may be lose and need replaced, or you have a vacuum leak.

you mean not firing no spark on 1,2 cly.or no change on rpm when you pull 1,2 if you have spark on it ,means no gas or your plug totally worn out

run fault codes and look for MAP/MAF sensor and accelerator position sensor problems

Since you changed the sensor we will assume it is working. When you disconnect it you put the computer in limp mode which stops it from using sensor values. If code 300 is the only code we will assume the coolant temp sensor and others are ok.
I would check fuel pressure with a gauge next.

could be the bad catalytic converter.

Hi.it sound a lot like a ignition coil coils tend to do that if its got a crack it Swell when the temperature rises

Even tho the ignition seems ok, I'd check the ignition cables to the plugs. Sometimes these break down over time... it will idle and drive ok, but when you need power for a hill, or acceration, that's when the wires faults start to show up.
A quick test is to put the car in drive with your left foot on the brake FIRMLY while you press the accerator... if the miss and lack of power shows up, it's usually the ignition cables to the plugs.
k

What have you done so far? Does your van have electronic ignition or points? If the latter i'd check/replace points, capacitor & white, low tension wire inside distributor. Also check the spark plugs (all four should have the same grey/brown colour) & H.T. lead resistance, especially if the fault occurs under load/acceleration.