Good morning,
I have a 1982 Oldsmobile 98 Regency Sedan with a 5.0 307 Oldsmobile engine with 55,000 original miles. The carburetor has been rebuilt by a professional electronic quadrajet rebuilder, fuel pump recently replaced, water pump replaced, new radiator, new PCV valve, new spark plugs/wires/distributor, vacuum lines are in excellent condition and verified to be so, and catalytic converter has been removed (no inspection requirements on an antique vehicle in Virginia).
The engine fires up with a few cranks when it is cold and idles smooth. The engine accelerates like a dream as well. Once the engine has reached operating temperature, it has a rough idle but still accelerates fine. The rough idle seems to "surge" slightly...almost like the engine is breathing in and out. The car is also much harder to start when the engine is warm. Any ideas as to what could be causing this? Again, it is mainly after the car has warmed up and I come to a stop.
Thanks,
Tyler
Malfunctioning EGR valve. Clean or replace it.
https://www.partsgeek.com/z6sx7y6-oldsmobile-98-egr-valve.html
I have replaced the EGR valve and this did not fix my problem. It was the original EGR so it needed to be replaced anyway. Any more ideas of what my issue could be? The car accelerates and cruises like a dream but once I come to a stop, it stumbles and the engine RPM fluctuates slightly--almost like it is breathing in and out. Thanks.
From your description, it sounds like a vacuum leak. Check the brake booster hose ( intake manifold to booster) for looseness and cracks. With the engine idling, spray some WD40 or carb cleaner around the intake manifold to see if the rpms change. At idle, the engine has maximum manifold vacuum that would be affected by a vacuum leak that would not affect it as you accelerate and the vacuum equalizes above and below the throttle plate.