I am looking at flights from SFO to MEX. One transfer allows only 30 minutes in LA, which I think is insufficient. Another gives us 1.5 hours in Puerto Vallarta. Is that enough? Do we have to go through immigration there? If so, do we have enough time (my wife is a slow walker so we can't be expected to rush to the front of any line)? We want to land in MEX at a decent time to catch the bus to Puebla and do not want to take an overnight flight.

1.5 hrs in Vallarta should be plenty of time for a layover, unless your flight in is seriously delayed.

30 minutes in LA probably isn't enough because you will probably have to switch terminals and go thru security again.

PVR can get clogged up at immigration if you happen to land at the same time as one or more other incoming flights, since it is a smallish airport.

30 mins. for anything at LAX would not be enough imo!

If you are flying Alaska it's probably enough as most/all of their flights to Mexico are in the same pod.
Curious about going on to Mex (DF) that way. Not sure where you are flying from but Mexicana has great connections out of many West coast cities including SFO & LA. As an Example I am flying SFO to DF to Zihuatanejo for $298 including taxes. I leave SFO at 11:30 PM & arrive DF about 5:00 with the time change. I have flown Mexicana for almost 25 years never having a bad experience.

Stewbear,

We're getting too old for overnight flights to Mexico even if we do suffer them to Europe. But the prices given by Mexicana seemed very good until taxes were added, at which point they were no better than other airlines. In fact, at that point it was better to fly to Puebla (our ultimate destination). The problem is that the connection in the Houston airport is very short and it is a change of terminals.

My problem now is to find an agent who can book me the flights I found on ITA.

Yeah The Taxes make no sense. $100 SFO to Zihua & about $200 to Guadalajara. Must be set in each local.
Have you tried Kayak for flights? If nothing else they are good for comparison.

Flights I found on Kayak, which I use regularly, are more expensive and less convenient than what I found on ITA.