Asking advice for an ongoing issue with my 2005 Volvo S80 AWD 4dr 2.5T Turbo Sedan.
Engine: 2.5L I5

It's a used car, in good condition. The CARFAX is thorough.

I bought the car in February 2019 and in April 2019 the car started stalling and going into limp home mode.
The check engine light came on, bad acceleration, RPMs spiking, idle very bad, and engine stalling.
After doing some research on the symptoms, I guessed it was the throttle body.

• When I took it to the mechanic, they diagnosed the issue as the wiring harness, and they replaced that.
• In May 2019, the car started going into limp home mode again. This time the shop replaced the throttle body but they installed a used part. (They lied to me, because I specifically asked them to install a new part.)
• In October 2019, the car started going into limp home mode again. The mechanic use the warranty to replace the throttle body again. (They installed a used part again.)
• I drove the car out of the parking lot and drove for about a mile when it started going into limp mode again. Took it back, they replaced the throttle body and the cables for it.
• A week later in Nov 2019, same thing. They replaced the throttle body and it went into limp home mode again within about a week or so. They told me the battery was the issue.

(I got a refund from that place, thankfully!)

• I got the battery replaced at another shop.
• After leaving the shop, the dash/turn signals stopped working. A fuse blew, so I got it replaced and the dash/turn signals started working again.
• Took it to a mechanic that specializes in Volvos, his diagnostic identified the throttle body as the issue. Because the last shop was using refurbished parts, it was continuing to fail. He replaced the throttle body with a brand new part.
• In about two days, the car started going into limp home mode again (but the check engine light was not turning on). The mechanic ran another diagnostic and the computer confirmed it was not a throttle body issue. The mechanic is currently inspecting it and I'm waiting for an update.

Couple of other points:

• When I shut off the engine and start it up again, it will correct itself about 60% of the time.
• "Reduced engine performance" notification appears on my dash.
• When limp home mode starts, the idle is bad, acceleration is bad, the RPMs spikes and the engine will stall.

Total Miles: 186,731

• Spark plugs were replaced at 119,416.
• Air filter was replaced at 166,893.
• Fuel filter was replaced at 166,893.

Here are some ideas I have:

• Mass air flow sensor
• Spark plugs
• ECM failure
• Fuel filter
• Fuel pump?

Does anyone have any suggestions for what the issue may be?
Thanks in advance for any advice you can give.
I can also get the codes from the previous invoices for the repairs that were done, but the car isn't showing codes anymore.

 

No idea really but I's sure change those 70,000 mile plugs before I did anything else, that's close to the end for OEM plugs and you may not, or may, have those in it.
Coil packs should be refreshed too..

I think the first step is to get good spark, then look at fuel issues.

And Buy a few yards of various vacuum tubing sizes and start replacing them.It's time.