94 Pontiac Transport Surges

1994 Pontiac Transport, 3.1 V-6.

Problem is intermittent and happens about one a week.

It causes no computer codes to appear.

Problem: For a period of about 30 seconds, the engine cuts out/surges once a second. It then returns to run normally.

Its not the Transmission, as putting the transmission in neutral doesn’t affect the problem.

Its acts like you were shorting out the ignition once a second for 30 seconds.
It happens at all speeds (20 - 60 mph).

Took it to a shop. They could find no problem.

To this point, it has happened about 10 times.

What you describe is like the engine rpm limiter that normally acts in Neutral when you try to floor the throttle: revs up to around 3500 rpm, then cuts, comes back, cuts....try it just to see.
No real idea if this function can go awry in such a way...does that happen at any rpm...or some precise rpm in every gear. WOuld you check if there is a change in rpm indication when that happens?

...mmm..and if that occurs around 3500 rpm in any of the gears, then I'd think the transmission gear switch might be shot and let the computer think transmission is in neutral when in fact it is in gear, hence trying to limit rpm to 3500...but that should throw a code, I think....
well..just thinking out loud..anyway tell us what happens next.....