Two months ago I had cylinder two misfiring. I had spark plugs replaced, also ignition coil on cylinder 2. Engine purred like a cat. Today I suddenly get cylinders 1 and 2 misfire. After one minute pause and restart things go back to normal. Since the ignition coil on cylinder 2 is two months old, what else can have this effect?
Thanks!

Edit: 2005 S60 T5 w. 155k miles

 

what year is your car, what engine? What grade of gas do you buy? as to possible causes a few things come to mind - 1) fuel trim is off - air leak, dirty throttle body or MAF 2) fuel pressure is off - sensor, regulator, pump, relay etc 3) wire harness to the coils/connector issue 4) head gasket (any signs of coolant loss, oil consumption etc?).

 

Thanks for posting.
2005 S60 T5 w. 155k miles, regular fuel, added Fuel Injector Cleaner a week ago. Throttle body was cleaned three months ago, MAF 2 replaced (Bosch). I think two other sensors were replaced at the same time - have to look up which. Car was checked for air leaks too, smog test few weeks ago. Oil and coolant OK. No other error messages except P0300,301,302.
Almost sounded as if the car didn't have fuel for a minute. After that, ran smooth again. CEL came on during the trouble, went off again.

 

Start by running premium. T5s have a minimum octane rating of 91 - regular fuel is 87. See what happens when you fill up with 93 (that will mix with the regular to bring its octane up). I'd look into testing the fuel pressure next if it continues. relay, regulator, sensor, filter etc.

 

Thanks, will do. What relay, regulator are you referring to?

 

fuel pump relay and fuel pressure regulator. When fuel pumps start to fail, they can draw too much current for the relay which then overheats and opens leading to a loss of fuel pressure. fuel pressure regulators have a vacuum diaphram in them which can tear leading to a loss of fuel pressure at the fuel rail. Both can create misfires under certain driving conditions. Also, right about 2005 Volvo went to a variable speed fuel pump which uses a pressure sensor - not sure what your model's design is - but again its a component that would need to be tested. Testing may involve measuring fuel pressure during a driving cycle or during start up and idle.

 

Car drives normal again, no error codes. Filled in some Premium gasoline and drove around without any hiccups or errors. Seems most of the possible causes you mention would cause a more permanent misfire? I might have to wait till it shows again....