Engine runs rough lack of power, disconnect sparkplug wires #2, and #3 runs the same

Do a compression test. Maybe that motor needs major repair.

the code is for random misfire, multiple cylinders, as you've replaced the plugs and leads then I would check the coils and the fuel injection

• Check Engine Lightflashing
• Rough running, hesitation, and/or jerking when accelerating
• In most cases, there are no adverse conditions noticed by the driver
• In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power (especially during acceleration), and a decrease in fuel economy

OBD diagnostic tool

First, have codes read to narrow possible causes. clean Idle air control valve or replace. TPS failure or "dead spots" send wrong signals to ECM. A blocked cat., low fuel or pressure, O2 sensor bad, sparkplug and wires faulty are some of many reasons.

code 66 is the a/c pressure switch. which will not make car run rough and stall unless its back feeding power. run engine with ac off and unhook connector to high pressure switch. the most common reason for running rough could be a bad sparkplug or sparkplug wire, check the wires and plugs also check dist cap and rotor for arcing. and last is how old is the o2 sensor, a bad o2 sensor can also cause this problem.

Oxygen sensor only report the condition of the engine the rough running condition can range from a worn sparkplug wires to worn sparkplugs to valve problems to injector problems. with the cadillac deville a tune up should be the first attempt to smooth the rough idle with the inspection of the cap and rotor cap and rotor do have a tendancy to arc internally and create misfire so does sparkplug wire that can leak spark voltage to ground and create misfire. the spark plug wire especially if they are brittle and hard can create issues

IF OIL LEAK RED IN COLOR.TRANSAXLE AXLE OIL SEAL LEAKING.HOW MUCH OIL PUTTING IN THE ENGINE TOO MUCH OIL FOUL OUT SPARK PLUGS.YOUR CAR USE 4 QUARTS OF OIL PLUS NEW FILTER.

The error code p2146 says fuel injector group A supply voltage circuit/open problem.The p2146 error code is related to the wiring in the valve cover that going to the injectors.It is part of the gasket and comes as an assembly.The wiring/gasket assembly for the valve cover is the most common cause for this problem but you disconnect the injectors and check ,if the code comes up again then injectors are also faulty. you will need to remove and install valve cover to test each injector. For this one at a time, disconnect both wires from each injector and insulate the terminal ends so the circuit will not short to ground connections. ---------------------- And for the error code P0202 the code says :-- Injector Circuit Malfunction - Cylinder 2. Its #2 injector circuit malfuction.Looks like either bad injector cylinder #2 or maybe an injector wire disconnected or shorted out.
---------- Check and possibly clean the connector on the injector and the connector itself.
It might just be loose.And that is causing this errors. ------- Keep updated with any more query.Thanks.

oxygen sensor

1991-1994 2.9L and 3.0L Engines Firing Order 1-4-2-5-3-6 1995 And Later 3.0L V-6 With DIS Ignition System Firing Order 1-4-2-5-3-6
4.0L Engines Firing Order: 1-4-2-5-3-6 DIS Ignition System