Toyota Repair: 93 Toyota Pevia idle surges, stalls, starts rough, pevia, egr system

Question
I have a well-cared-for 93 Previa AWD Van with 220K kms that has seemed choked/suffocated when starting for some time. A few weeks ago it began idling rough (surge up, down, then stall). I now have to keep it revved to keep it running. It will idle erraticly one day, and the next day it's perfectly normal again.

I had new plugs/wires within the last 10K miles, changed fuel filter. The Toyota dealer also checked computer diagnostics/codes, fuel pressure, coil and found nothing. They're saying it's because the valves need adjustment - would this explain the type of intermittent behaviour I'm seeing? It's 5+ hours shop labour and parts at the dealer just to find out ... I'm not convinced. What else do you think this could be?

Many thanks.
John

Answer
I don't agree that the valves are the problem or it would be there all the time, once valves are out of adjustment they tend to stay that way.
Have the EGR system checked for a possible sticking EGR valve.
Also have them check for a possible air leak in the intake system.
If the distributor cap and rotor were not replaced have them checked for possible cracks.