random engine misfire - P0300

[djirene4206]

Have a 1996 Buick century special 3.1L vin M. Car seems to do fine at hgiher speeds, or at least the misfire is less noticable then. At idle, if you listen to the exhaust, there is a steady spitting sound and it smells somewhat like gas. I have already done an injector coil test, havent done a balance test yet. Tested fuel pressure - it was within limits (40psi, engine off, 38 running, 50 with vacuum disconnected from regulator). Hooked up my Actron scanner, erased codes, and they come back after about 2 days driving. Tested injector drivers from PCM, they test fine. The Actron showed me on the data list that long term fuel trim was briefly around -16%, which is at its lowest maximum authority. Should I wait and see if it stores a fuel trim code? I guess i am at a loss. What could be causing this? Cam sensor or its reluctor ring? Hole in fuel tank / bad o ring seal on sender assembly? Or could it just be dirt on the fuel pump strainer? Finally, before my car stored this code, it seemed like it would surge at takeoff up to 20 mph, with little change in the gas pedal. Thanks in advance for any help.

[richtazz]

Try unplugging the MAF sensor. When they first start to act up, they will cause the symptoms you describe without tripping a code. I would also check to see if you're losing coolant, as your engine is known for intake leaks that will allow coolant to leak internally into the lifter galley, causing the oil to appear milky/cloudy and overfull.

[glewis]

I have a 96 Century also! Had a similar problem that drove me nuts for over a year. I tried almost everything everybody suggested. I finaly broke down and took it to a reliable mechanic.
He thought it was just a tune up, did that and it was still misfiring. He took a smoke machine from an old train set and started pouring smoke in different spots lookin for a vacuume leak. He found one. Now get this!! One of the O rings on the fuel injector was cracked and mangled. He replaced all the O rings on all the fuel injectors. ended up costing me over $400.00 for that visit, not to mention all the money I spent on new parts and sensors trying to cure that problem.
If you done have smoke, try spraying some brake cleaner and listen to engine changes as you spray different areas.