Make sure the PCV system is in good shape, including the oil-separator
screen below the PCV valve hole.
now to troubleshoot:
Then get engine warmed up and disconnect/plug all vacuum ports on intake
EXCEPT the fuel pressure reg.
Then stop, disconnect IAC harness, start and check that engine idle is
about 500-550 rpm. If above that or still fast idle, you either have a
vacuum leak or someone has messed with the stop screw.. but if cold idle
is good, I doubt either
I suspect, if idle is good (lower than 650) with IAC plug disc; and the
Check engine Light comes on with key on, then goes out, and doesnt show
with engine running, you may have a bad Throttle Position Sensor (TPS) -
or wiring to it. Bad TPS doesnt set the CEL in EECIV (or most of them,
If it is still the adjustable version you need borrow a DVM and set it to
.90 to .99 volts with the throttle on the stop screw.
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
Not likely that the intake problem would/could cause that.
You either have a bad vacuum check valve or a vacuum leak in
the hvac. This is beyond the manifold. If you have a large
leak in the hvac control, it could result in high idle.
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