OBD code 33, 91 pontiac grand prix
91 Pontiac grand prix 93k miles, upon start
up it idles normal, then idles pretty high and
check engine line comes on and then engine
starts to surge, always dies at idle, there is
hesitation in accelerating and decelerating
plus after driving a bit on the road the check
engine light eventually goes away but once I
let off the gas it comes back on, brand new
map sensor and iacv, still won't run right
Check for vacuum leaks. Use some starting fluid or carb cleaner and spray along the intake manifold gasket, and around the throttle body base gasket. If there is a leak the rpms of the engine will pick up. Do this on a cool engine where the rpms are at idle.
If you are still diagnosing, try replacing the ECM. I had the same symptoms (and a few others), did all the normal "tune up" stuff and finally fixed it by replacing the ECM. MY car was a 5L '91 Trans Am and it was NOT throwing any codes when the computer part broke down. Good luck.
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