Good Morning, (sorry for the long post)

I have a 1990 240. Every two years it fails the emission test, so I buy a new Cat (bosal), it passes, and I drive on for two years until the next test. In the last 6 years, I've put on 3 cats...

My next test is coming up in 8 weeks, so I'm considering installing some new parts to address a few issues and hopefully extend the life of the new cat I will have to install.

Here's my plan:

1. replace the fuel pressure regulator (car will sometimes stumble in the morning for 10 min then fine)

2. replace the idle air control valve (often idles surges after putting the car in park after a highway drive)

3. clean throttle body and replace gasket (check intake hose for any leaks)

4. clean/replace flame trap if needed

5. I am also considering a new AMM. This is a part I have replaced with used models in the past. I have always hesitated to shell out for the new one, but am willing to do if it will help address the cat and other idling issues.

My thoughts are that installing all of these parts in conjunction with a new cat will smooth out the ride and keep the cat going a bit longer.

The plugs, Cap and Rotor, Spark Plug Cords, and speed sensor have all been replaced within the last two years. I replaced the Fuel Pressure regulator about 6 years ago but have never replaced the idle air control valve. In-tank pump, fuel filter, used AMM, air filter, check valve, O2 Sensor and fuel pump have all been replaced before.

I guess my questions are:

- will this help extend the life of the cat and smooth out idle issues?
- Is there anything else I should consider?
- Is it worth it considering I may only keep the car for another 2 years if it
lasts?

I don't mind spending some money to make these improvements and keep my 240 in good health, but also don't want to throw too much money at a car that may only last a little while longer.

Any help, thoughts, comments are appreciated and again, sorry for the long post.