1995 Previa with supercharged engine will "miss" gently without showing either an engine light or a fault code. I have studiously tried to tie the miss to environmental conditions such as cold, heat, humidity, hot/cold engine, etc. but can not find a consistent clue. It show rather dramatically when accelerating in the lower speed ranges and makes it quite exciting to join highway traffic at times. Somewhat consistent at around 60 mph. It is erratic in showing itself, some days the van is a perfect rocket ship, other days it is borderline dangerous.

Only other clue is erratic cruise control as well, but not in conjunction with the acceleration problem. Some times both, some times either, some time neither.

Dealer admits problem but clueless how to solve without an engine code etc......

That's a tough one! Have you tried another dealer? Sometimes you can go to two or three different places and get totally different advice. The only other thing I can think of is to try to find the code you can check out one of the Previa 1991-97 Repair Manual books at a local bookstore or online. It might have some good information. Or you can try to go to the site http://www.alldatadiy.com/ they charge you about $30 for access to repair information and codes. Hope I helped a little. (IMG:style_emoticons/default/57.gif)

The problem you describe, WALDOA7, is virtually identical to the problem I just solved. I have a '97 Previa with supercharger and 133k miles. The short answer is that I replaced the spark plug wires, distributor cap and rotor. The problem disappeared COMPLETELY.
I am pretty sure the following explains what was happening. The problem got to the point where at 50 mph if you had low engine rpm, high gear and then tried to accelerate, the van would hiccup, cough, miss (or whatever other words you want to use) rather severely. It was to the point I was really concerned about destroying the drive train. I used my scan tool in capture mode and discovered that the problem always occurred at about 2000 rpm when the supercharger was up to about 6 pounds/minute. At this point the timing would jump from 30 degrees to about 10 with the drive train hiccuping. Research I did said that at about 2000 rpm the computer starts to monitor the engine for knock. If knock is detected it immediately changes the timing to a very low default value to protect the engine. The air flow sensor, throttle position sensor, knock sensor, fuel pressure regulator and compression all checked out good as far as I could tell. I believe the problem was that one of the spark plug wires was arcing a little to the engine block (probably all the time) and this raised the electrical "noise floor" for the knock sensor (which is less than a foot away) but not to the point of tripping the knock monitor all the time. The knock sensor is a low voltage sensor (approximately half a volt) so it doesn't take too much electrical "noise" added to the signal to trip the monitor. I believe an engine at low rpm which is trying to accelerate is most likely to have some knock even if it is not enough to normally trip the knock monitor. Add a supercharger trying to ram air into the engine along with the electrical "noise" and the larger signal output of the knock sensor is enough to trip the monitor and cause the problem. As an electrical engineer this explanation makes a lot of sense even if it is not 100% accurate. A problem like this is difficult to locate because the engine control is a feedback loop where almost any sensor can cause a problem.
By the way, when I disconnected the supercharger relay the problem also disappeared but only because there was less real "knock" for the sensor to detect. Who wants to drive without the supercharger?!
Hope this helps if you still have the problem!

Did a scan on my vehicle and got the same result. Going to do a replacement of the parts soon to see if it would fix my problem.