1991 - 1993 Gm 60*V6 engines (cutlass, lumnina, grand prix, regal) were diagnosed as having bad injectors straight from the factory, that cause what is termed "Phantom Stalling".
It had something to do with the injectors electrical load and the pulse duration. Unfortunately, I don't think a recall was ever done. Most owners who swing a wrench, have replaced the injectors with aftermarket injectors, or have gotten injectors from a '96 and up GM 3.4l engine. In most cases this stops the phantom stalling.
Your loping or hunting idle may be due to a dirty idle speed control passage. Carbon clogs the passage and causes your idle speed motor to hunt for a stable idle.
If you decide to go with stock GM injectors, be sure and get injectors from a 3.4l DOHC engine not a 3.4l OHV (3400), the flow rates on the 3400 are lower and will drive your computer nuts trying to compensate for the decreased injector duration. You'll be running extremely lean and your 3.4 won't like you!
Oh and before you ask the question, "couldn't I just get larger injectors for a performance boost while fixing the issue?"
Nope.
Not unless you plan on running boost. and boosting a 3.4 dohc is no small task.