A couple of weeks ago, my 2000 Limited (AW4, 4.0, NP242, red, bumper stickers, geeky licence plate, etc.) developed a cold running problem that hasn't entirely been solved. At this point I'm trying to narrow down the culprit, but wanted to get some suggestions before I go drop a bunch of cash I don't have on new sensors.
Symptoms: during the warm-up phase, there's a stumble (no stall) at idle accompanied by audible pre-detonation and bogging down when in motion. This happens when the temperature gauge is between the first and third mark above the bottom line, and disappears completely (except for the odd pre-detonation when moving) once warm. Note that it does not happen when the vehicle is completely cold, and I can force it to behave 'correctly' by stomping the accelerator flat to the floor when it acts up. No OBD-II codes are being thrown or stored.
Tried so far: major throttle body cleaning (helped tremendously) by hand, cleaned IAT sensor with penetrating oil (also helped tremendously), checked IAT continuity (good, no obvious ground leaks). Just doing these things alone solved somewhere in the region of 90% of the problem.
Suspects: IAT, spark plugs (need to be replaced anyway, doing that later today), possibly the coolant temperature sensor (not 100% convinced on that, though), O2 sensors (83000 miles, time for them as well). The TPS is not a suspect at this point since it doesn't feel like a blown TPS does (been there, done that).
If I had a spare $300 right now, I'd just go through and replace all of them at once - but that's not currently an option. Anyone have any ideas on where to look next? I'm planning on pulling the IAT later this morning and giving it another hit of penetrating oil before I start the vehicle, but am not convinced this is going to completely fix the problems. Sanity check, anyone?
Symptoms: during the warm-up phase, there's a stumble (no stall) at idle accompanied by audible pre-detonation and bogging down when in motion. This happens when the temperature gauge is between the first and third mark above the bottom line, and disappears completely (except for the odd pre-detonation when moving) once warm. Note that it does not happen when the vehicle is completely cold, and I can force it to behave 'correctly' by stomping the accelerator flat to the floor when it acts up. No OBD-II codes are being thrown or stored.
Tried so far: major throttle body cleaning (helped tremendously) by hand, cleaned IAT sensor with penetrating oil (also helped tremendously), checked IAT continuity (good, no obvious ground leaks). Just doing these things alone solved somewhere in the region of 90% of the problem.
Suspects: IAT, spark plugs (need to be replaced anyway, doing that later today), possibly the coolant temperature sensor (not 100% convinced on that, though), O2 sensors (83000 miles, time for them as well). The TPS is not a suspect at this point since it doesn't feel like a blown TPS does (been there, done that).
If I had a spare $300 right now, I'd just go through and replace all of them at once - but that's not currently an option. Anyone have any ideas on where to look next? I'm planning on pulling the IAT later this morning and giving it another hit of penetrating oil before I start the vehicle, but am not convinced this is going to completely fix the problems. Sanity check, anyone?
