Volvo V70 intermittent loss of power/speedo not working

[Heavyhorse]

Our 2000 v70 auto estate with 185k on the clock has never missed a beat. Today the exhaust started to blow at the beginning of a 40 mile journey. car was normal besides the slightly noisy exhaust when we stopped. When we started the return journey, the car felt like it was in winter mode with slow acceleration and gear shifts, there was a clunk ( like going over a pothole minus the pothole) and the speedo needle dropped to zero. A few times it came back up and then clicked and went off again. After 20 miles I was approaching traffic lights and had a loss of power, car was running but no acceleration at all and I limped it through the lights, speedo came back on and it picked up momentarily and then started running really rough like a cylinder wasn’t firing properly. Stopped the car and debated whether to phone breakdown. Started it up again and it was fine , just the exhaust a blowing , and drove it the last 20 miles with no issues at al, and speedo stayed working. I’m wondering if anyone had any ideas or if the exhaust could have affected a sensor ? I really thought the car was knackered when it was running so rough but the fact that it went back to normal after wards is confusing. It started up no problem every time I stopped and restarted it. Any thoughts appreciated. Don’t want to get the exhaust replaced if the engine/gearbox is going to pack up!

[volvo again]

The speedo gets its signal from the abs module so not sure why this stopped working unless it's a loose connection at the module, although I would have thought this would trigger the abs warning light.
Exhaust blow might have triggered an O2 sensor and put it in limp mode, but depends where the leak is.
Any eml light showing?

[Heavyhorse]

Yes it has a faulty abs sensor on the rear passenger side wheel , it has been like that for a few years and hasn’t caused any problems so far. I know it should have been fixed before now ...

[Heavyhorse]

Meant to add I’ve been ignoring the abs light as the garage told me it was a faulty sensor which wasnt causing problems. The car did change its abs message a couple of times today from abs service required , to brake failure service urgent and back again, but this is also not unusual.

[volvo again]

Interested to know how it passed MOT with abs light on...

[Luxobarge]

Front passenger side ABS sensor is where the speedo gets its signal from. This will also provide the ECU with a vehicle speed signal, so it's possible the ECU is also complaining about lack of this signal. First port of call is to change/fix that sensor - I can't believe you've a) got through any MoTs with the ABS light on and b) are prepared to drive with inoperative ABS. Get it fixed!