Jim Grant's Tech Tips
Ford Bronco, Idle is Too High
Q: I have a ‘92 Ford Bronco (full size, not the Bronco II) with a
fuel injected 5.0 V-8 and a 5 speed manual (5th being overdrive). It has
over 145k miles. Rear ABS brakes, power steering, cruise control. The
problem: The engine idle is way too high. It is 1,500 RPM. The gas pedal
sometimes sticks in the morning and it takes a good tap on the pedal to
depress it. I have checked the accelerator linkage and sprayed all moving
parts with WD-40. The idle is still too high. I adjusted the idle screw,
no affect. When moving the throttle body linkage by hand, it feels as
if a valve inside is sticking. I was told by someone else that it could
be the oxygen sensor malfunctioning and sending the wrong info. to the
engine management system. I suspect it has more to do with a sticking
throttle body valve.
agree with you,. The high idle problem may very well lay with the sticking
throttle. But spraying the outside may not be the cure. Remove the air
inlet hose and take a look at the throttle plate and surrounding area.
From your description it is very likely all you’ll see is a bunch of black
carbon. It is common for carbon deposits to build up on the throttle plate
causing it to stick and cause the idle speed to be erratic. The fix? With
a soft bristled brush and rag in hand spray the area with some WD-40,
yes the same stuff you used on the linkage. Then scrub away at the throttle
plate and the surrounding area until it is bright and clean. This is often
the fix for a sticking throttle and erratic idle problem.