For the last 4-6 months my 01 L (26kmiles, stock) has had a constant rough, notchy, twitchy idle. Numerous visits to the dealer resulted in a new MASS, plugs, airfilter, IAC (all under warranty). These fixes seemed to help but the problem remained unresolved. The L has run fine except for idle (neutral, park or drive). So this past Monday went back to the dealer and asked them to look at this idle problem again. A super nice SVT tech came over and watched the truck idle...said the idle was too rough and not ACCEPTABLE...took it immediately into the shop. He did the the full set of Ford diagnostics through the diag port (I watched)...finally when he got to the oscilloscpe type firing graph...could see "RANDOM missfiring"...He said it wasn't the coil packs or plugs or O2 sensors since the "missfiring was irradic or random"...if it was a coil pack etc. the missfire would be at the same plug or plugs...the Tech suspected the crankshaft sensor and the part was ordered...NO computer error codes were indicated during any of this testing...he said that the microsecond timing of these "missfires" were too small and fast to be picked up by the computer and logged. So today, took the L back in (part came in)...the Tech had to remove the AC compressor to get to the "crankshaft timing sensor". Replaced the sensor...cranked it up...MUCH smoother in idle...
Evidently this sensor (same as on all 5.4 engines) was the problem but time will tell as we all know. Even though NO scan code errors were given, the actual realtime firing graph pattern told the dirty story...Hope that this might help some of you with similiar idle problems...the Tech did comment that these engines will not idle "dead smoothe" but too rough of an idle is another issue. Will let you'll know if this is a permanent fix.

 

Good info!

Also helps to clean that bad-boy, as it's been known to cause hot start issues during the summer. Take off the bolt that holds it in, pull it out, wipe it off, replace. Dunno why that works, but it does...