Stumble at idle after ABS engages

"Mike Copeland" <mcopeland.RemoveThis@REMOVETHISpobox.com> wrote in message
news:4402fff9$1@kcnews01...
> 89GMC wrote:
> > 89 K3500 7.4 th400 with abs, just replaced the module when I got the
> > truck, abs does seem to be working. The problem is after the abs kicks
> > on the truck will start stumbling at idle, it doesn't stall but sounds
> > like it wants to. After I go at normal speed for a few
> > minutes(anywhere from 30mph on up) it goes away. The truck runs/idles
> > fine other than that, just had a tune up. Any ideas?
>
>
> May not be ABS related but a vacuum issue. Your vacuum booster may be
> trying to tell you something. Put a vacuum gage on that you can read
> while driving and hit the brakes and then see how long it takes to
> recover vacuum.

Start checking vacuum lines, 17 year old truck. especially the one going
from the PCV
to the base of the throttle body at the throttle body, as well as the large
line going from
the vacuum tee to the cruise control.

Whitelightning
 >> Stay informed about: Stumble at idle after ABS engages 

I don't see any vacuum lines running to the brakes. There are lines
running to the power steering pump though, I busted out my service
manual and it confirms that there were two types, one with vacuum boost
and one with hydro boost... guess I got the hydro. Could it be the
power steering pump trying to recover pressure causing this? It's
really odd... BTW the vacuum tips were helpful anyway b/c although I've
been through and replaced them before, when I double checked I found
another real brittle one that snapped in my hand, so one less thing to
deal with down the road....
 >> Stay informed about: Stumble at idle after ABS engages 

"89GMC" <dziarcak.RemoveThis@gmail.com> wrote in message
news:1141240187.237161.78700@p10g2000cwp.googlegroups.com...
> I don't see any vacuum lines running to the brakes. There are lines
> running to the power steering pump though, I busted out my service
> manual and it confirms that there were two types, one with vacuum boost
> and one with hydro boost... guess I got the hydro. Could it be the
> power steering pump trying to recover pressure causing this? It's
> really odd... BTW the vacuum tips were helpful anyway b/c although I've
> been through and replaced them before, when I double checked I found
> another real brittle one that snapped in my hand, so one less thing to
> deal with down the road....
>
Ok you have hydroboast system. key off pump the brakes untill the pedal
gets hard
and count how many pumps it takes. Could be the "accumulator" is not
holding enough
pressure. Have you had any problems with fluid loss from the power steering
system?

Whitelightning
 >> Stay informed about: Stumble at idle after ABS engages