Transmission rebuilt, now misfires & a dead cluster?

[CamoYoshi]

Hello folks,

Got some weird things going on with my 2002 S80 T6 Executive (yes, it has a TV screen and mini-fridge in the back, instead of the middle seat).

Had the transmission rebuilt and when I went to pick up the car, I noticed that the gauge cluster, with the exception of the Check Engine and Seatbelt light don't come on. I drove the car home as I already prior to the transmission swap had issues with the text display in the lower left (completely blank) and a couple bulbs out. Was going to get that fixed but the transmission went out first. No weird behavior on the drive home, which was mostly highway driving.

A day later, I went to drive the car and when in drive at a stop it was idling kind of rough. The check engine light did not come on. The next day it was on and I checked and there were 4 pending codes for:
P0300
P0302
P0304
P0305

However the misfires only happened a couple of times since then but haven't happened since. My guess is perhaps stale fuel (The car sat for about 6 months before I could pony up $4000 for the trans rebuild, though I did add a full bottle of stabilizer to a almost full tank of 92). I haven't pulled the plugs yet to check on them but I will likely do that soon, I suspect the plugs are old and need to be replaced anyway.

However the cluster is still dead. No backlighting, no gauge movement, no turn signal indicator (signals work fine otherwise).

Based on the XeMODex flowchart for DIM troubleshooting they recommend sending the DIM in for a rebuild (based on the fact that the sunroof and windows roll up and down without issue). However I'm not 100% certain since both the misfires and the gauge cluster started at around the same time.

It's worth noting this transmission place forgot to reattach the charge pipe at the front of the engine when I went to pick it up so I suspect a rush job was done.

I've tried to look over engine grounds and the like but didn't find any that weren't attached. Someone else recommended a ECU reseat and to check for bent pins but I think I'd be having way more problems if that were the case.

Anyways, just looking for some guidance or suggestions on what else to look at before spending $500ish on a DIM rebuild and perhaps $200-$300 on plugs and coils, haha. Anyone else had these issues before or have any ideas about these symptoms on where to go next?

Still new to the Volvos from a mechanical perspective so apologies if I'm missing some things; very much still learning and hello from Seattle!

[oragex]

You may want to test the alternator and battery as a first step for the misfire. This video below gives you an understanding of the voltage value. Also try inspecting all power and ground connectors, you have one behind the engine bay fuse box, also a ground behind the top of the engine. Because the entire engine was removed for the job, many things could have been installed improperly

Yes, the DIM goes bad on a 2002 but you have cheaper places than Xemodex, look up on Ebay for electronic module repair services. A local TV shop can also fix these for even cheaper if you remove it (see youtube) and bring them the electronic board alone. The car battery must stay disconnected during the process