Vaccum leak?

I have a '97 Cal 2.2 that has had an occasional stumbling problem from idle to just over 1,000 rpm. I have tried several times to locate any vaccum leak, but have not found anything. Yesterday, I noticed that the o-ring was missing from the dipstick cap - oil fill tube. I have not replaced it yet, but was wondering if that could cause a vaccum leak through the PCV valve / crankcase.
Any thoughts?
Thanks

Use a can of carb. cleaner spray along the edges of the manifold. Also spray around any other areas where vacuum can leak. If you find a leak the engine will smooth out when the spray hits it.

Did you take a look at the map sensor or try to tighten down the TB by chance?