So...I've been having tons of fun with my 1999 S70 (96K miles, non turbo) these days. I really enjoy the car, but have as of late really not been having a good time. Let me give you the rundown, and if anyone has any suggestions, please let me know. My wife is the main driver of the car, but I drive it fairly frequently (just so the narrative makes sense).

Saturday, July 5th
Wife turns on car to go to work. Car shudders badly, ETS light comes on. We take car to dealership (car drives in "Limp home" mode). They replace the master relay, send us on our way. Car returned to us on Monday, July 7th.

Wednesday, July 9th
Wife turns on car in the evening (had been driving normally between Monday and Wednesday). Same stuff (car shudders, ETS light, limp home mode). Take back to dealer on Thursday morning. Dealer replaces ETM and some of the gaskets under ETS warranty. When installing new part, they tell me they are having difficulties getting the new ETM to initialize, but they manage to get it working. Car returned Friday, July 11th.

At this point I can tell the car is running smoother. Slight shudder that used to happen when returning to idle at stoplights is gone.

Friday, July 11th
Turn in car the next time after returning from dealership, bad shudder, ETS light. Turn on car again 10 minutes later, car runs normally, ETS light still lit. Drive around the block, light still lit, normal throttle response. Return car to dealer that same day. No limp home mode.

This time the dealer says that the communication between the ETM and ECM isn't working well, so I need to replace the ECM. ECM is on backorder, so they return the car to me (sans codes, since they erased them) on July 16th. I take it directly to my normal Volvo shop (Volvo Specialists...very experienced guys). They find no codes, no issues, do some tracing and find that dealership swapped the ETM and ECM relays, ETM relay bad (when swapped back, car won't start). Shop replaces ETM relay, puts ECM relay in right place. They test drive it, no issues. I get it home, start it several times (between last night and this morning), no issues.

I call dealership and they say that the two parts are equivalent, and that they knew the ETM relay was burnt. They had swapped them on purpose (for what purpose, I have no idea).

OK, so a few questions:

• Does this sound like the ECM is causing this? This car has about 96K miles on it, so I'm having a hard time believing that the ECM is going bad this quickly (not that it can't...just everyone says it's unlikely)
• Are the two relays truly equivalent? I know the plugs are the same, but are the internals the same? It bothers me that they released the car back to me in this config without telling me.
• Anything else you can think of? I've put close to $350 into this issue already (fortunately the ETM stuff was under warranty), and I'm not convinced the issue is gone.

Please help!

As an epilogue (I hope), I have had no issues with the car since replacing the relay. The car seems to be working fine again, and honestly, throttle is a lot better since they changed the ETM.