Car De-celerates randomly

What is your question?

Hi. My car has been sporadically de- accelerating for the past few months. I will have my foot on the gas and the car will slow down. It will usually do it a few times and then run ok for a while and then start again. Took it to one mechanic who couldn't figure it out - did a fuel injection cleaning - not any better. Took it to the Honda dealer yesterday and they said they want to try replacing the Throttle body for $900, but are not sure if that will fix it. Doesn't seem to do it when I'm going over 55 mph, but I don't go that fast very often so it could be a coincidence. Any thoughts? Thanks!