surging/hunting 91 626 mazda in Drive...ok in rvrs

[gfharris729]

91 mazda 626 w/ auto trans...
Engine Surges/hunts when placed in Drive or any forward gear....
Will cut off if throttle is not floored.....
Runs Normally in reverse or when in neutral....
Suspect something akin to a vacuum leak relating to what used to be called a "modulator valve"... Find nothing in my "Chilton" manual..
Help!

[gfharris729]

Any helps or suggestions will be appreciated...
P.S. I replaced the "Throttle position sensor potentiometer" as a precaution; no help.

[rnatyte]

I dont know how well you know mazdas, but a very big problem they have is the connecting hose from the mass air flow sensor to the intake. if the hose has a crack in it and you take off the crack will open and mess the air flow up. The way it act in reverse and park tells me the motor runs fine. take the hose off and bend it in all direction to check for cracks. I hope this will help you

... how is the trans.?