So basically I was out for a short ride in the city in my 08 XC90 3.2 2008 AWD when I stopped at a red light, when the light turned green I started to accelerate when I immediately felt something went wrong in the engine, loss of power and engine vibration while driving and at idle. And if I would press the throttle pedal a bit more for a faster acceleration then would the "Slow down or shift up" message appear with the orange triangle of warning.

I drove off the road and stopped to try to figure out what had happened, I couldn't decide what happened directly but a similar situation experience which had happened almost 7 months before I could think of worn Ignition Coils or worn sparkplugs. Although the sparkplugs have been replaced before 40.000 Km at the dealership, and by that time I had one coil worn which caused a misfire and it was also replaced by the dealer service center.

So what do you people think of this? could it be an ignition coil again? if yes why would ignition coils fail frequently? is it normal?

I would also highlight that I have had a check engine light on for 4 months and when I asked the dealer to diagnose it and read the codes, they told me that it was one O2 sensor not working well, but they didn't advise me to replace it as it could be an expensive repair so they just erased the code, but after 2 days it showed up again of course. I would also mention that after I faced the misfire yesterday I noticed a bad gas smell coming out of the car so is it a normal symptom of a worn ignition coil? or could it be a worn Oxygen sensor that doesn't work totally anymore? and could the oxygen sensor cause the engine to misfire by itself?

thanks in advance for any comments and opinions below.

 

Your first step would be to scan the car with a compatible scanner. With that info you might/should be able to formulate a reasonable, rational diagnostic path. Anything else would be a guess at this point.

 

not sure about a dealer who says to ignore an O2 sensor code. There are multiple codes related to O2 sensors and sometimes they are triggered by things other than a bad sensor but as hoonk said, start by getting the codes scanned again. Not sure where you are located but its pretty easy to scan your own codes (if you are near an auto parts chain store, they likely will lend you a scanner or you can buy one for as little as $30 (Harbor Freight sells them) which are good for CEL / emissions type codes. Its as simple as plugging the reader into the port (usually under the driver's side of the dash), turn the key to position 2 (engine off, dash lights on) and follow the menu on the scanner. You can then google possible causes for the codes.