Toyota Repair: 91 previa le all-trac follow up, air flow sensor, fuel issues

Question
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Followup To
Question -
Subject          91 Toyota Previa LE all-trac          
         
Question          Car has been "breaking down" plugs for 6 months causing car to miss gently at first then violently after a time following new spark plugs. The period of time varies from 2 weeks to a month before car runs so poorly especially after warm and when climbing hills but also when in forward with brakes at a traffic light. The problem mirrors a fuel injector clog but fuel issues have been
checked and ruled out by regular mechanic. Regular mechanic then changed out distributor cap, plugs, and wires on a few occasions. He also considered and ruled out vane air flow sensor before giving up. Dealer replaced O2 sensor and considered velocity position control sensor and wiring harness while replacing plugs.
Car ran fine for 3 weeks but is back to missing at traffic lights and violently cutting out and surging when climbing hills while accelerating. One friend thought maybe not distributor cap but actual distributor sensor where engine is connected might be the problem. Any ideas?          
         


         
Answer          Has the distributor rotor been replaced? If not I suggest you try that and let me know the results.

Follow Up Question: The distributor rotor has been changed out twice with the cap.          
Answer -
It still sounds like an electrical engine misfire, try replacing the igniton coil.

Hi Ted,

I spoke to my mechanic about the ignition coil and he agreed it might be a good thing to try.  He wanted to give you some additional information: van appears to be "leaning out" and starving combustion.  Newly replaced plugs break down after some time.  Not the typical carbon around fouled plugs but a "whitish" break down of plugs.  Is there a way to explain this?

Thanks, Mario

Answer
It's time to look for a leak on the intake system, check all the intake hoses, I think I may have advised doing this already, I don't remember,check for any vacuum leaks, attach a vacuum gauge to get a manifold  vacuum reading it should be about 15mm/HG on a vacuum gauge at idle and the reading should be steady and not fluctuate.