95 1.3 no power

car runs good, does start a little hard when cold, when you leave a stop sign and accelerate, there is a terrible flat spot, the harder you step on the gas, it does nothing, it just very gradually gets up to speed, if it is warmed up, and you slow down to approx. 35mph or above, it is not nearly as bad. check engine light is on, and I get a 31 for a code, I have replaced the sensor in the air cleaner, that did not change anything
any IDeas would be much appreciated, Thanks
P.S. car has auto trans

is it an automatic? sounds like maybe its transmission is stuck in third or fourth gear.

Yes it is an automatic, but it is shifting through all the gears

have you ever had the automatic transmission fluid flushed and refilled? aside from that i dunno, i drive stick most of the time

No, I have not. I bought this car late last fall with a bad engine. It sat for 2 years. I bought a used engine for it and just got it on the road a few weeks ago.

get that done then, if you leave it go for too long you'll get a ruined transmission. check your junk mail for a coupon, a lot of times you can find an oil changing chain that'll do it for $50