A few years ago I worked on a car that did exactly the same thing! It turned out that a rodent had chewed through one of the wires to the EZL. It's been a while but I think it may have been the green wire to the TDC sensor? I'll have a look at a 420 as soon as I get to work on Monday to see if it jogs my memory. The funny part of the story is that two days after I repaired the wire the rodent ate through the same wire again!!! I could see where he nibbled at the shrink tubing I installed following the solder repair, but he must not have liked the taste, so he ate through it right next to the repaired section. Let me know what you find.