I have 04 monte carlo 3.8 non supercharged. Since I have had it (6 months now) it has been stuttering while accelerating in 55 to 60 mph range. 90% of the time it happens I have a passenger but other times not. The past week or two when I start it periodically it will act like starting but die immediately. When this happens I try starting again and it starts as normal. It does not throw check engine light. I have changed plugs and wires. Took gas line off and made sure had pressure when turned key on but didn't have gauge to check how much though it shot a stream over my back. Took off all coil packs and they looked ok but unsure how to test those. Any suggestions would be appreciated. It is automatic and has around 169000 miles. Also have sprayed vacuum lines with ether to see if leaks and seems fine. Also air filter is clean.

 

I would be suspicious of a dirty or worn out MAF sensor first. I suggest pulling it off and cleaning it with MAF sensor cleaner to start, but it may need to be replaced. I would also clean the throttle body screen and replace the fuel filter if that's never been done. Just because it doesn't throw a CEL doesn't mean there is not a code stored. It's worth checking. The big chain auto part stores will do it for free. Don't think the passengers should have anything to do with it.

 

transmission may not catching when switching gears, if the stuttering is you not accelerating vs engine losing power

 

Possible clogged cat, if it is still the original. How is your gas mileage? Maybe a leaky fuel pressure regulator which will make the car run very rich.

 

Thanks for all the replies I will start with maf sensor and go from there. Question about the cat convertor I had one clogged before on different vehicle and it would get red. The question is does it always or was that just an extreme case? I get 22-24 mpg not sure what this car is rated for