Check for vacuum leaks. The gasket was known to blow out between the throttle body and the intake manifold.
The idle speed on a 1987 Chevy Celebrity is controlled by the engine computer, there is no way provided to adjust it.
I have 91 chevy k1500, It does this, Sometimes it will idle a few minutes, then jump to high idle and check engine light comes on, And sometimes its as soon as i start the engine... I was told it was a vacum leak, But im no mechanic
carb problems, adjust the idle screw and see if that helps
The idle speed is read by the Engine Control Module(computer) and adjusted as necessary by use of the idle air control in conjunction with the throttle position sensor. There is no separate idle sensor as such.
IAC (idle air control) valve may be bad. Located on the passenger side of the throttle body.
check the soleinoid
You can not adjust the idle screw, it is sealed off at the factory. If you are having a high idle problem check for a vacuum leak or a bad idle air control valve. These will commonly cause a high idle.
Could be a vacuum leak.
check for vaccum leaks
If this happened all at once, check the vacuum lines. A cracked or broken line will cause high or rough idle.
It depends on the year. If you can't get the idle down, check for vacuum leaks. That seems to be a primary cause of high idle, especially for the TBI engines.
A vacuum leak could do that. Did it have a high idle before you changed the throttle body? Any codes?