Expedition - 5.4 - erratic idle
Got a (new to me) Expedition 4x4, 5.4, 230,000 km, K&N Filter intake system. No other mods. In general it runs very well, but has an erratic idle and surges (at idle).
At first the vehicle was throwing lots of codes. due to the nasty shape of the K&N filter (very oily & dirty), I cleaned that up, rest, and tripped some MAF related codes. New MAF.
With all that done, now I own trip 171 & 174 codes. Plugs confirm it's been running lean for a good while before it got it. I reset the PCM (disconnected the battery for 15min). The power is a little better, but I still have the wild, erratic idle. It doesn't like to drop below 2000 rpm... after 10 sec- 20 sec, it drops to 1100, then moments later down to idle, where it surges (wha, wha, wha, wha). While driving, it doesn't kick down below 2000 rpm, so it pushes along me when coming to stops, and I have to ride the brake, or shift to neutral.
I checked all the hoses for vacuum leaks and all looks good. Replaced the PCV for the heck of it. No change in codes or idle.
So... any hints? What's left? TPS & IAC valve?