I’m the original owner of a 2005 Mariner (3.0L V-6, 114K miles). We live in Central TX, so we are just starting to experience cooler weather (40’s - 50’s at night, 60’s - 70’s daytime). At this time of year and through the winter, this Mariner develops an annoying rough idle. It is more like a strong vibration when in Drive or Reverse, not really a miss in the engine. Increasing the idle speed with the accelerator pedal helps, and it does get somewhat better as the engine gets to normal operating temp, however if the day is cold (30’s or 40’s) it doesn’t get better.
I’ve changed the plugs, changed the IAC valve, and cleaned the MAF sensor a couple of times, with no improvement. We almost exclusively use Exxon or Chevron gas, which should have good fuel-injector cleaning additives, so I sort of doubt the injectors are at fault. I’ve had a local mechanic check to see if any codes exist, but nothing shows up. This has gone on for 2 or 3 years, but it was not like this when the car was newer.
Any suggestions as to where to turn next?