Rpm's drop from 3000 to 100 and then back up to 3000 when at 30mph

i have a 2007 access cab, 6cyl, at. when at approx 30 mph the rpm's will drop from 3000 to 100 then immediately back up to 3000.
toyota charged me $350 for a complete tune-up and this did not help. they checked the pressure of the fuel pump and it was good and the fuel filter was clean. i'm not sure what to do? i find this to be a security issue. can anyone suggest what to look for or do?
thank you in advance

 

What the hell amounts to a tune-up nowadays anyway?

 

you can also try cleaning that sensor with brakeclean or contact cleaner just do not touch the element with anything but the solvents

 

(IAC) Idle Air Control Valve possibly.

 

Thanks going to pass that on to my neighbor friend who is having this problem with his 07 taco. I'll post an update when he gives me one.

 

If you are going to spray the MAF use ONLY MAF cleaner, do not touch the spray nozzle on the sensor wires or you will have to buy a new MAF. I agree with JimmyH, you may need to clean the Idle air control valve. Sometimes they stick and will cause your engine to stall. I don't know what all was done in your tune up but you may also want to try cleaning the throttle body as well when your air filter was changed, it never hurts to clean the throttle body during a tune up =) hope this helps some.