I need advice on my car. It bucks going down the road on 2001 Ford Taurus

My car bucks going down the road. (Shuts off) but keeps on going. The rpms go up & down along with the speedometer. I've had the plugs & wires changed, new ignition coil, new injector. My mechanic has swapped other parts from another Taurus & nothing has changed. It ran good for a couple weeks & it started acting up again.
Any suggestions?

Asked by for the 2001 Ford Taurus
What codes are stored in the ECM? Without codes you're just throwing parts at it which seems to be the case.
I had auto zone read my check engine light & it came back trouble shooting p1309 & p0340