Cadillac Repair: 91 Cadillac Eldorado Barritz 4.9L, cadillac eldorado, vacuum lines

Question
I'm having a problem with my car.  I am not getting power when I step on the gas and it is backfiring. I cleared the computer and the the only thing that comes up is E099 History.  I took my car to the Cadillac dealer and they told me I needed a new exhaust, (converter to the back) and to change my spark plugs and wires. I did that, but the car is still running rough.

Answer
Re-enter diagnostics via simultaneously pushing and holding for 3 seconds the OFF and WARMER buttons and the release them.

When you see ECM?

Press and release the HI (^) (fan up) button and you will see ECM DATA?

Keep pressing and releasing the LO button until you see ECM CLEAR CODES?

Push and release the HI button and you will see ECM CODES CLEAR. Wait 3 seconds and turn OFF the ignition. Drive the car and see if the code returns.

Look for any vacuum lines that may have gotten knocked loose in the engine compartment.