Toyota Repair: iacv & throttle body sensor, toyota tacoma prerunner, 2002 toyota tacoma prerunner

Question
I own a 2002 Toyota Tacoma prerunner 2wd with a 3.4 v6. Prior to my replacing the timing belt I had a problem with the engine light coming on. My mechanic put it on the computer and it came up that the idle air control valve and the throttle body sensor. He told me that the throttle body was only opening at 75 percent. Since then the check engine light comes on for maybe 100 miles then turns off by itself.3 months later it comes on again, this has been going on for years. Im thinking that the IACV is bad which would explain the check engine light and the variance in idle but my question is what about the throttle body only opening at 75 percent any help would be greatly appreciated you can reach me at  thank you in advance John

Answer
The IAC vlave would have an effect on the idle but would not necessarily turn the check engine light on, the TPS however would, it would help to know what the diagnostic code information was or is, do you have any code numbers available or can you get them.
How did the mechanic determine that the throttle is only opening 75%?