I need to let my engine warm up before the automatic transmission will go into gear. What is the problem?

First, welcome to the pool. Hope we can help solve your problems.

Make, model and age of your car will help us come up with a solution. Your location also helps in this case. Are cold or really cold where your at?

One of the cheapest fixes I know is a pint of a good transmission cure. This helps lub the seal and expands dried out "O" rings.

If that does not help, take it to you local oil change place and see if the have the facilities to do a transmission flush and fill.

Transmission fluid does not last for ever.

i had a 60's model chevy that needed to warm up before it would go. never figged out why.if its high milage then an oil change + filter would be in order. maybe call a trany builder in your neck of the woods and ask them a ? or 2. call at least three and see if you get the same answer