I've had similar problems that have turned out to be a bad fuel pump.
Although I'm not sure how that would explain the fact that in gear/out of
gear makes a difference.

I also took the car to a garage once after being unable to go above like
20mph on the highway.  They suggested it was the mass air flow thing (the
exact name is escaping me).  They replaced it but the car died similarly 2
weeks later and the second garage diagnosed the fuel pump.

Just a past experience, but the hesitating and refusing to accelerate sounds
familiar.

Connal

>  I have a 1985 Vanagon camper with 130,000 miles and no previous
>serious problems with the power train. Recently, the van has been
>experiencing periods where it loses power but does not stall. When
>attempting to accelerate, it feels as if the gas is being choked off,
>yet if put in neutral the motor can be easily reved up. When
>reengaged, however, there is no power and the car will not accelerate
>(the van does not stall). If on level or going down hill, the car
>will move slowly, but if going up a grade, there is little movement.
>Appears to always occur from a cold start. Can occur when the gas
>tank is near empty or full (usually use Exxon regular; however,
>currently using Exxon high test, which has not helped). What is
>frustrating is that the problem is intermittent. The car will run
>>perfectly for a few days and then the problem recurs. Since the car
>is presently used mostly for traveling to and from work (~5 miles),

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