Hi-I had the fuel pressure regulator, spark plugs and wires changed-my car from that point ran great until it got warm, then it shakes, when I press the accelerator it will go then nothing then go again-I have to feather the peddle to keep it going, It barely makes it up a small incline-i found out the cat was completely plugged and my husband decided to take the cat off and replace it with a straight pipe (emissions are no longer required in Washington state) but the problem is still there. It is throwing random misfires and the check engine light flashes once it gets warm. I am replacing the EGR valve today but I am at a loss because my car ran fine until i replaced the plugs and wires and FPR
Lets look at this from an outside perspective. Your car ran fine until you touched it. So instead of throwing parts at it, lets recheck our work. This may not sound like fun but is important in order to rule out the obvious.
Remove each spark plug and examine it carefully. Pay close attention to the spark plug gap to make certain it did not accidentally get closed. If just one spark plug was dropped and hit the floor, there is a chance that the gap is closed. Also inspect the plug wires to make sure the metal connector is all the way at the end allowing it to connect to the plug securely.
Spark Plug Gap
Spark plug gap adjustment: 0.060 inch.
Measure the gap, Fig. 1, between the center electrode (4) and the side electrode (3) terminals. An excessively wide electrode gap can prevent correct spark plug operation.
Spark Plug Wires
Since you also replaced the spark plug wires there is a good chance that you installed the wires on the wrong ignition coil. So lets double check that also. Using the diagram to correlate the coil number with the cylinder number. This would be the most common cause for the issue you are having. Simply put, the wires are crossed and connecting with the wrong cylinders. Double and triple check this. *Note: The provided image is for the 3.8L engine.
Spark Plug Wire Replacement