7 month old thread now.
Problem has remained *solved* since installing a PCV valve. Car runs fine.
A little history on this 2001 Grand Prix GT (there's another thread somewhere with details): My wife and I bought this car in 2003 (for my wife; I owned a `97 Bonneville). We sold it to a neighbor in 2010. She gave it back to me (no cost) in 2016 with check engine light and codes for emissions and ABS brakes. Ultimately the Air Injection Reaction pump, relay, and check valve needed to be replaced, as well as the missing PCV, and the EGR got replaced a couple times, and I replaced the ABS controller with an identical one from a salvage yard, and that took care of all the emissions problems and the check engine light and codes. I did a TON of other work rebuilding the driver's seat, replacing the carpet, engine & transmission mounts, and a ton of other maintenance items to get it back into shape. It makes for a pretty good extra car for us, now with 209,000 miles on it.
