1988 Beretta NEEDS HELP!

1988 Chevy Beretta 2.8L with 150,000 mi.
No power to accelerate and poor fuel consumption.
I have removed the catalytic.
I have changed the coil packs, plug wires, plugs, TPS, IAC, MAF, Fuel filter, Ignition Module.
I ran codes and got a 33 and 34 and 42.
I put a new MAP in and still having same issues and wont rev over 4000 rpm.
Still getting code 42 (EST circuit). What is this? Where is this? And how can I check it and correct it?
Please help! I need this car.
When I put it in gear it wants to stall and won't accelerate. It sputters and backfires intermittently. Eats lots of gas and wont go above 30 mph or 4000 rpm.