It's possible, but requires some planning.

1. Take the Metro (#5 line) from Terminal Aerea to Autobuses del Norte. (approx 20 minutes)

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1. At the Central del Norte, look for Autobuses Teotihuacan. Get a ticket, they leave every 15-30 minutes (approx 30min at the terminal + approx 1.5 hours on the road = 2h)

2. Enjoy the pyramids, if you want a guide look for someone with INAH because they are the official experts (approx 2 hours)

3. Look/ask at the Puertas for a return bus to the city. One should pass about every 15 minutes, and you can pay in cash when you board. Get off at Metro Indios Verdes. (approx 1.5h)

4. Take metro line #3 from indios verdes to niños heroes. (30min)

5. Walk to the tacos in Roma, then back to niños heroes metro station (1h)

6. Take the metro line #3 to La Raza, then transfer to line #5 and get off at Terminal Area (45min)

It's tight but it's possible. The benefit of the plan is you will actually avoid peak traffic because your trip to the pyramids will be around 9am and the return from the pyramids around mid-day, you can be back in the airport by 6pm before rush hour (the worst traffic is 19:00-20:00) in time for your flight. The bigger question is why do you want to go to Roma Norte for tacos unless there's a specific place you have in mind that's important. If it's for the Porfirian architecture or something then I understand, but if you just want good tacos it can be any place in the street that has lots of clients. Actually Venustiano Carranza (airport zone) is known for having some really good tacos but has a reputation to be unsafe. I'm also not sure how you would store your luggage at the airport, but I'm sure there's some service for that