Buick LeSabre, 2002, 279k, 3800V6, virtually all highway miles, runs good otherwise, brief stumble and code P0300 with flashing Service Vehicle Soon light when letting off the power at highway speed. None when back under power, or at any time around town at lower speeds or idle. Higher rpm at idle too, +10 degrees F. Thoughts?
20 year old car, may be the coil packs are going out. This is a random misfire code that sounds electronic. Replaced the spark plugs lately?
As @doc suggested, it’s time for a full tune up.
While you’re at it, change the fuel filter & pressure test the fuel pump too.
check the misfire topic in our FAQ
So the coil packs on this car sit above the exhaust manifold, and they break down over time due to the heat. When you open the hood, theyre on the left side toward the front, labeled 14, 25, 36. Cheap and easy part to replace, they set right on top. I actually put zzp higher voltage ones in mine for alittle over $100 (OEM is completely fine though) when mine went bad. Its probably the coilpack, this isnt uncommon on the 3.8 (ive owned 2).
PS - The reason i got higher voltage ones is bc i intend on doing more mods in the future. The car is no longer my daily.
No. I have been lulled into inaction by smooth running and top fuel economy, until now.