I've got a 2001 volvo 8.1gi (496) in a Cobalt 262. The engine has what I can only describe as an RPM flutter or fluctation from 3200-3700 RPMs. The engine fluctuates about 50 RPMs inside this RPM window. The engine idles flawless and once the RPM's are above 3700, the engine runs smooth as silk all the way to 4600. The engine also runs perfect up to 3200 RPM's. The problem doesn't seem to be throttle cable/lever related, and the flutter is always present between 3200-3700. You can actually feel the engine fluctuate as if you were moving the throttle lever slightly up and down. Any ideas what may be causing this (ECU and/or fuel injection problems?)?

Thanks, Jake

start with changing fuel filter,,,

The fuel filter has about 30 hours running time on it (it's a Volvo OEM). You think it could possibly be a bad/defective filter?

Plugs, wires, fuel filter. Especially if the plugs and wires are original.

Ditto. My Merc.was doing the same thing but noticable only at idle and it was a fouled plug. The ECM sometimes can't compinsate at all RPM ranges.

I changed the plugs last season, but I didn't change the wires. You guys got any certain vendor(s) that you prefer for ignition parts (plugs/wires)?

496-8.1L engine owners here on OSO, remember, we take brand new sets of plug wires off of new 496 engines we rework for our coil relocation kits and we sell these brand new sets of take-off wires sets for $85 per set of wires. You can't beat that price with a stick! so if you need new plug wire sets, let us know, Raylar has lots of sets in stock.
Just a money saving suggestion.

Best Regards,
Ray @ Raylar

I appreciate it Ray. BTW, does anyone think this problem could be from a bad Throttle Position Sensor (TPS) or possibly a failing fuel pump (fuel pressure fluctuating in problem RPM range)?