Volvo Forums - Volvo Enthusiasts Forum - 2001 V70 T5 - Rough idle, engine dying, coolant leaking

I have a 2001 V70 T5 with 160K miles in TX and have had problems recently with the car dying when at idle, low RPM and even when coasting at low speeds. Please keep in mind I have very little mechanical knowledge or experience, but I know from past work I have had done that taking it to be a dealer/shop would be a total cash-i-ectamy on my wallet.
Local Mechanic told me to replace vacum lines which had hardened and cracked. I replaced all the lines that looked bad visually. Still have problem.
Q1. Is there a link or instructions anywhere on how to check the system more thoroughly for vacum leaks?? (I think I should start here)
I took it to dealer and after agreeing to a $120 diagnostic fee. They will NEVER work on my car. Sounding somewhat amused they said “You have a lot wrong with this car, we can NOT diagnose it until you replace the PCV valve. It will be $1,100, would you like us to replace it?" I might as well have gone in pulled my pants down and bent over , that’s the feeling I got because I replaced the PCV valve myself which took me 4 hours and cost me around $130 in parts..(Dealer gave me wrong PCV valve which was bolted on the engine before I realized it was for the wrong car, so + 1-2 hrs scratching head and 2hr round trip back to dealer) Car still dying..
Looked online to see if I could find any solutions and suspected the MAF or ETM.
Auto Zone gave me these codes free of charge:
P0121 - Throttle pedal position
P0102 - Mass air flow sensor
I disconnected the Mass air flow sensor and found that my car was idling very rough still, with RMP fluctuating from 800-1200 but NOT dying with the MAF sensor disconnected.
Replaced Mass air flow sensor ($125 + 1hr labor), spark plugs($35), and wireless electrodes ($55) (spark plug boot' but not coils packs) Car was still idling very rough and was back to dying again.
Luckily, I thought to replace the fuel filter ($25 + .5 hrs) as well and found the old one clogged up, and barely dripping out dark brown fuel when flipped over.
I started the engine up and it was purring... The rough idle seemed to be gone, and the engine was not shaking and struggling as before. Although engine was running more smoothly the RPMs were still fluctuating from 800-1000 rpm. Took it on the road and found that check engine light, service light, and engine system service required message had disappeared. Then they reappeared about 10 miles later and the car is back to running very rough in low RPM and coasting at very low speeds. It now feels like the car is jerking/surging forward when approaching a stop in sync with the fluctuating RPMs. The engine is dying less than before, but still has a very hard time idling and it seems like the timing belt is struggling to turn and is barely moving. When at idle the exhaust seems very weak then very strong in sync with the RPMs. It feels like it is building up pressure then releasing it every time the RPMs increase.
To compound my problems I have a coolant leak which has gotten worse lately. I have looked at the hoses and under the car and have not found the leak. I have read it can leak in many spots. It seems to leak when I am driving and not when parked. It has progressed to adding coolant every other day.
Q2. What coolant components are prone to leaking? Where all should I check for these leaks? Do my other symptoms along with this leak point to head gasket problems?
Q3. I am not sure what to do next. I have looked at cleaning the ETM and will probably try this next. I am not eligible for free replacement from Volvo for this 2001 model. If cleaning does nothing how much should I expect to pay for the replacement part/programming?
Could it be a bad Catalytic converter? Should I try cleaning this? Does a gallon a lacquer thinner in the gas tank work for this? Soaking it in soapy water do the trick? Anybody have any aftermarket cut and clamp recommendations?
Any advice is greatly appreciated. Many thanks!