Ford: E250 Hesitation/Stumble off idle

com (gale tyler) wrote in message news:<google.com>... 

I guess I should clarify... Van runs perfectly until you release the
brake and let it start to roll, then it stumbles. If you hold the
brake and load the engine, it will not stumble. We have replaced the
speed sensor in the diff, due to bouncing speedo. Anyone had this one
before?

Gale

"gale tyler" wrote
 

How's the idle in park with your foot off the brake? And if you stick your head
under the dash, is there a hissing sound ONLY when your foot is off the brake?
Sounds like it could be a leaking vacuum booster.

When you step on the brake, an internal valve seals off the front section of the
booster (it now has vacuum in it), and opens the rear section to the outside air.
The air pressure now in the rear is what helps you push against the master cylinder.

When you take your foot off the brake, the valve should seal off the outside vent,
and open the inner valve, allowing the vacuum to equalize between the front and
rear sections. If the outer vent isn't closing properly, you'll have unmetered air
leaking into the intake manifold via the outside vent, the internal valve, and the
brake booster's big vacuum hose.

"MasterBlaster" <Nobody'Place> wrote in message news:<OSi8b.124875$telusplanet.net>... 


Blaster,
I tried putting it in gear while holding the E brake to eliminate
that... Still does it. No hissing either... This one is really
challenging!!! The Ford garage said it may be the sensor on the
speedo head??? The EEC is not getting the signal??? Ever heard of
this one??? Thanks, Gale