Weird s13 auto trans problem

[sviellvoicae]

Ok so my brother recently picked up this s13 with a bad trans(auto) it wouldnt do anything other than 1st gear and reverse. So we swapped it out with a trans that came from a perfectly running 240. While driving the vehicle will downshift every time your take your foot off the gass pedal. Even if you take it off 75% but are still giving it a little it will downsift. It does this in every gear. I should note that its a trans froma 94 vert and its on an 89 coupe. So dohc to sohc. thanks

[Infinitiguy19]

Check the Throttle Position Sensor.

See the Service Manual for more help: Nicoclub.com/FSM