Started engine, normal idle, but when you try to accerate the engine falls flat...either in or out of gear. replaced fuel filter and checked TPS. Continuity is per specs, but voltaqge is backwards...5 v closed and 1v wot. Any ideas?

new spark plugs this decade. (a tune up?0
the filter is part of all 60k tuneups. letting it clog wrecks good pumps.
my wild guess, its lack of fuel flow, do to old filter.
or low fuel pressure.
car is identical to a Corolla. so is not unique or rare as some Geo cars are.
the cam belt not changes, invites valve kissing piston tops. BOOM
end of engine. (costs more to fix then worth of car)
the word is bogging, my engine bogs
if if bogs WOT (wide open throttle) and dont catch up < ITS NOT THE TPS. ever.
tps bad causes short bogs, called hesitations.
The map sensor , is what measure air flow and the ECU matches fuel to this air flow.
my guess, is it does that, but fuel pressure is like 15PSI, bad.

Is the check engine light on? you could have a bad ignition fail sensor, TPS sensor, or bad o2 sensor. it could also be a bad mass air flow sensor or a vacuum leak. without a code to help pin point the problem I'd start by checking those things first. Maybe try unplugging the mass airflow sensor and start it up and see if anything changes.

Have you checked the fuel pressure with a gauge, and is the check engine light on ? TPS check out with a meter ok ?

You could pay a garage to diagnose the problem cheaper than throwing more parts at it.
The problems may be connected or they may be different issues.
Yes I would change the oil and filter, but first I would make sure the fuel system is not dumping too much fuel into the cylinders.
The O2 sensor helps the computer decide on how much fuel the engine needs, along with the other sensors. And you said you have already replaced the O2 sensor.
A mechanic would take a scanner and "read" the sensors and look for something out of normal range.
The fuel pump and fuel filter are off the list as far as causing a rich mixture goes.
I would start with the rich mixture and then see if fixing that issue takes care of the no start when hot issue.
Change the oil and filter first, and see if the injector is on too much.
You can watch the spray and tell - at idle it should be very light.
Also look at the engine temp - is it warming up to normal 195 degrees? Can you tell if the fuel pressure regulator is blown and pouring fuel into the throttle body ?
Without a scanner its going to be more difficult, but not impossible to diagnose.
Let me know what you find out.

TPS wears in spots and can cause intermittent problems like you described. Try turning off the car and unpluging the TPS. Start the car and see if smooths out the idle/reving problem while the TPS is unplugged. If yes replace the TPS.

Sounds like you may need to replace the TPS (throttle position sensor), that will cause the idle not to fall in between shifts.

Try this----there should be two or three coils in the distributor. Check these coils with your ohm meter. The car will run with one bad coil in a "limp mode". However, if a second coil goes bad, it will not run or start. These coils can be intermittantly bad so you have to check them when you have a no start condition. If you check when car is running well then you may not find the problem coil. What are the code numbers?

Replace the Intake Air Temperature Sensor.
Depending on your size Engine (2.4L, 3.0L or 3.3L) It should be located where the Air Filter is. When you take the cover off, it wil be mounted into the cover. It has the only wires going to the cover.
This sends information to the Computer which adjust the air/fuel mixture - causing surges.
The 2nd recommednation: to remove, clean and check is the Idle Air Control (IAC) Valve and replace if necessary.

Let me know if this helped....

KEEP IT SIMPLE,CHECK THINGS,LIKE,CABLES,ACCERATOR,UMMMMM,EVEN,WATCH THE TRUCK ON A SCANNER,LOOK AT AIR TEMP,AND IAC,AND TPS.GOOD LUCK

PO229 indicates tps circut inttermitent.
Po300 303 and 304 indicate missfires on cyl 3 and 4.. Was the fuel filter primed before starting the engine? If not ,remove and reinstall filter. Then prime filter with pump that is on fuel filter adapter. Once this is done restart and verify o/k