Hello,

I have a volvo S60 3.0 Turbo T6 with 230,000 k's on it.
Just replaced the cat as it was throwing error codes constantly and motor was cutting out. The new cat has fixed all this but i now experience a slight but sudden surging when accelerating normally from pull away.
Idle is also sometimes unstable when engine is first started and won't rev when you push the accelerator.

Any comments on where to start on diagnosing this would be greatly appreciated.

 

That sounds mostly like a mass air flow (MAF) sensor issue, but I can't imagine why tinkering with the exhaust system would interfere with that.

How long since you did the work? Did you disconnect the battery when you did it? If so, the engine controller has a bit of a learning curve to reset itself, but that shouldn't take long.

 

Thanks for your comments.
It's a week and a half since it replaced the Cat.
Yes I disconnected the positive lead off the battery while doing the work.
It has once since then actually cut out when I was driving very slowly through a Carpark just after starting.
Problem is that the issue is intermittent, worst kind of problem in a way!
Otherwise the car is running well most of the time.

I guess the most noticeable and consistent problem is it's uneven acceleration (surging) when pulling away.

Glad of anyone's comments.

 

check for intake air leaks and exhaust leaks (which can throw off the lamba control from the front O2 sensor)

 

I will check as you say.
Thank you.

 

I found the PCV valve was broken, (there was excessive suction at the tiny hole in the PCV valve cap) Upon opening the round PCV valve enclosure on the oil trap i found the rubber valve torn.

I replaced this part. (the whole Oil Trap and PCV Valve)

Car is no longer surging on acceleration.

However it is still stalling at idle and when driving or reversing at very slow speeds.

Sometimes i can feel the engine falter when cruising at speed too.

It seems to be worse when the car is cold.

If anyone has any comments that could point me in the right direction to diagnose this problem it would be much appreciated.

 

Just curious how your Volvo was reacting before you replaced the cat. I have a 2012 S60 T5 that is constantly throwing the inefficient cat code (P0420) and I've been wondering if the odd surging (or power cutting out issues) that I have when accelerating hard may be related to a bad cat. An expert at a muffler show says that a bad cat wouldn't cause that but I'm not sure.

 

I'm not sure, i am not really qualified to answer with confidence.
I do know that is rare for a cat to actually get clogged and block the flow of the exhaust gasses.
But if a cat is faulty it won't be as effective in stripping the polution out of the exhaust gas and then this will trigger the error code.

I would suggest looking elsewhere for a problem first because i changed the CAT and found no fix to the surging/cutting out issues i have.