1999 motor into 1991 XJ

As the title reads I put a 1999 4.0 into my 1991. I hydrolocked the old motor and got a good deal on the 1999. The only thing i took from the 1999 is the motor and exhaust manifold. We used the 1991 throttle body and the intake manifold. At first it ran rough at idle so I tried the tps because it got wet so i thought that would fix it. The idle problem was fixed but as sooon as I went to pull away it sputtered and the rpms dropped to around 500. I got it home and took the tb off and checked the tps out again. Now after its all installed again it wont run unless someone is pulling on the throttle cable. This has me and a ase tech stumped. Anyone on have any ideas?

MAKE SURE YOU DONT HAVE ANY VACUUM LEAKS AROUND INTAKE MANIFOLD OR HOSES,DID YOUR INTAKE MANIFOLD TO CYL.HEAD PORTS HAVE THE SAME SHAPE,SOMETIMES THE HEAD MAY HAVE SQUARE PORTS AND INTAKE ROUND.CHECK IDLE AIR CONTROL VALVE OR PORTS IN IDLE CIRCUIT IN THROTTLE BODY FOR OBSTRUCTIONS.

Check two things, The Idle Air Control Valve, and the oxygen sensor(s), if the oxy sensor gets wet at all then its done....are you using the 91 distributor and ignition parts, or the 99 distributorless system?

welll the 1999 isnt a distribulitorless system anyway that started in 2000. But yes i am using the distributyor from 1991

i replace the iac and the o2 sensor
do i have to disonnect the battery for the computer to reload?
i am really lost on this one now and it doesnt help its like 20 outside now.