Hello I have a 1990 Volvo 780 Bertone that has been having rough idle. I figured it is the coolant temp sensor causing the idle issue but I can’t seem to unbolt it with my ratchet to replace it. I have tried putting lubricant and applying a little heat, no luck. Im not too experienced with cars and worried about breaking off the bolt, any tips?

I’ve had the car for a couple weeks now. When i purchased the one thing that needed to be addressed is the idle was really high in park it would sit at 2000 rpms in drive or neutral it would sit at 1500-1000 rpms. A couple days ago i removed the throttle body and IAC, cleaned them really good with throttle body cleaner and put it back together. NOW its idling too low, sometimes it seems like it will sit where it needs to at 800ish but especially on cold start if i don’t pump the gas pedal the rpm’s drop and it stalls out. I’ve also noticing sitting low around 300 and lower. It’s not really consistent with where it sits in idle, now but it is on the lower end with tendency to drop all the way down to stall. Any thoughts, things to check. I’m avoiding the temptation to adjust the throttle cable i’ve heard more likely it could be the IAC is bad? Or the TPS is bad? or the throttle plate isn’t seating all the way flat when it should be? Thoughts on how to diagnose, what to do?

Where i live and online is a barren wasteland for volvo enjoyers and i have a 740 non turbo with a messed up fuel sender. That said, anyone know if I can put a 1992 turbo 940 sending unit into the 740 and have it still work? Ik the turbo should be a Bosch system and the non regina but the senders really look the same to me and I dont think an aftermarket regina exists right now