The car miss firing the first valve sometimes.

If your 96 E250 300ci was running perfectly and then started missing and the code is indicating a miss fire in cylinders 1 and 2, there could be a few potential causes. Here are a few steps you can try to troubleshoot and resolve the issue:

1. Check the ignition system: Make sure that the ignition system is functioning properly. Check the distributor cap, rotor, spark plug wires, and ignition coil for any signs of wear or damage.
2. Check the fuel system: Make sure that the fuel system is functioning properly. Check the fuel filter, fuel pressure, and fuel injectors for any signs of wear or damage.
3. Check the compression: A compression test can help to determine if the engine is getting enough compression to run properly. Low compression in cylinders 1 and 2 can cause the engine to miss fire.
4. Check the vacuum lines: Make sure that the vacuum lines are properly connected and not leaking. Any vacuum leaks can cause the engine to run poorly and miss fire.
5. Check the PCV valve: The PCV (positive crankcase ventilation) valve can become clogged or malfunctioning and cause the engine to run poorly and miss fire.
6. Check the EGR valve: The EGR (exhaust gas recirculation) valve can become clogged or malfunctioning and cause the engine to run poorly and miss fire.
7. Check the Engine Control Module: The Engine Control Module (ECM) controls the ignition and fuel systems and if it's malfunctioning it can cause the engine to miss fire.

It's important to note that some of these steps may require special tools and knowledge of the vehicle's engine system, so it's best to take it to a professional mechanic to avoid causing more damage.

Very possible the valve cover gasket is leaking or the valve cover itself cracked. Ford OEM Motorcraft parts and vanity license plates

Sometimes plugs break. If money is an issue, swap the plug to another cylinder to see if the problem follows it. Otherwise, you may have a stuck intake (or possibly exhaust) valve.

plug wire , plug or a valve. usually plug wire will cause a miss a valve if on intake side will cause it to misfire sometime back into the intake. the plug can sometimes fire and sometimes not so simple replacement would fix. compression check would tell if it is valve issue.

Of course it could be a defective plug or a failing coil for that one cylinder. A steady miss fire should set a trouble code.
You might take another look at the plugs and the connector between the plug and the coil. It could also be a fuel problem such as a fuel filter or O2 sensor.
You may need to hook a scanner to the computer and watch the sensors when the engine is cold compared to warmed up.

possibly wiring harness fault,sesor wheel installed backwards or an even fire/odd fire engine mismatched components

check your mass air flow and see if the screan if blocked with carbon buil up

Are your injectors all firing and are your plugs firing on all cylinders?
If you have a miss, is it being picked up by the computer as a miss on a certain cylinder?

check timing belt thats it lined up ok ,change the plugs and leads and if no better ,remove the head and grind the valves in ,checking the valve springs

check your fuel rail because it could be putting out only so many psi of fuel so do fuel pressure test check. also what kind of fuel are you using? sometimes could be firing order or timing sequence. better check that too because eventually if this turns out to be electrically related it would be best to perform a diagnostic scan on it to be safe.
good luck!!!