i have a 88 cougar with a 302 in it my problem ia s fast idle. i
changed the iac but still fast idle. any ideas so i wont keep replacing
parts i dont need to? when started cold it revs up then down till it
finds right rpm. but when hot, i keep a fast idle. i want to fix it
before i lose a ujoint as it jumps in gear. please help.
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.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.