Hey,
Ive seen the same thing on 4.7 vehicles...Heres a diagnostic concept.
Remove the large vacuum hose from the TB and block the vacuum port (you may
get a check engine light). Start the truck and try and get it to idle fast.
You might need to tee the vacuum line into your PCV to get the truck to run
properly. I am suspecting that the vapor purge system might have a weak
component /programming issue causing excessive air to get into the TB via
the vacuum port. A scanner can tell you how many counts the IAC motor is at
if you have access to one. My guess is it will be at full count (all the
way closed)...
Bruce Bridges
F&B
----- Original Message -----
From: <Sammon287@aol.com>
To: <dml@dakota-truck.net>
Sent: Wednesday, August 28, 2002 2:59 PM
Subject: DML: runaway idle speed on 2000 slt+
>
> My 2000 SLT+ 4.7L/ 5 speed has an annoying problem when venturing
offroad.
> It has done this since new, but since I rarely hammer the truck offroad, I
> have ignored it until now. When driving on a rough dirt road scattered
with
> small rocks, it feels like the cruise control kicks in, actually
accelerating
> up to 1500-2500 rpm. Stepping on the clutch lets the engine rev up to
> @2500rpm, which slowly drops as I come to a stop. Standing on the brake
does
> nothing to drop the engine speed, as it accelerates again as soon as I
> release it. Remember this is a man trans. I imagine this must be caused by
> some sensor/ throttle body actuator that is affected by vibration. This
would
> be a major safety issue if it was an automatic, but even with the manual,
it
> is impossible to drive smoothly on rough roads. I am reluctant to go to
the
> dealer (been there several times in 2.5 years) because they will never be
> able to recreate the problem. The truck wheels well at low speed (low
> gearing, LSD, and decent rear axle flex) as long as there is no high
> frequency vibration.
>
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