1996 960 Error Code P0410 and a rough take-off

[ryguy]

My 960 gave me this code this morning on the way to work, and I'm pretty sure I know why. A little googling tells me that it has to do with the air pump--an emissions consideration. My code reader is generic OBD-II, so I don't have the Volvo-specific code.

Here's what I was thinking the problem is: I was tinkering under the hood, trying to familiarize myself when the engine compartment, when I noticed how easily the airbox lid came off. It appeared that the plastic piece left that was hanging onto a sensor was just about the same diameter as an elbow pipe I had.

Here's where the stupidity starts.

In about 15 minutes, I had fitted a cone filter I had lying around onto the other end of this elbow pipe and made a makeshift intake. I always liked the sound it had made on my previous car, and I didn't see that I had removed any sensors with the stock-size filter and lid, so I figured I'd try it out. I drove it around the neighborhood and enjoyed the growl it now made at WOT, so I decided to give it a trial run.

This morning, during my commute, while I was idling at a stop light, I noticed my CEL had come on. The car seemed to be still running fine, so I drove it gingerly the rest of the way to work and connected my scanner when I got there. I got code P0410. I looked under the hood to make sure my makeshift intake was still in place, and it was. Upon looking closer I noticed that the intake pipe that routes to the front of the car also lead back to a part of the car I couldn't see. I'm guessing this is where that air pump comes in.

Here's my question to the Volvo gurus: Would it be wisest to put the stock airbox back in place, clear the code, and see if it comes back after some more driving? Or, is the Volvo computer simply freaking out while it sorts out why exactly it's getting more, but hotter air through the intake? Basically, was it a dumb move to attempt this with my 960? Are there any options out there for getting a more agressive sound out of the engine? I know it's supposed to be a luxury car, but I'm a young guy, and I don't want my Swedish barge to blend in TOO well...

One more thing: I have been noticing that when I step off from a standstill quickly, the engine will sort of stumble or hesitate, run roughly for a split second, and then take off smoothly. When I take off less aggressively, the roughness is less pronounced or non-existent. I am using 93 octane, as recommended. Could this be a clog in the fuel system, or are my plugs/wires bad? My car has 76k miles.