Timing belt failure OR idle air control valve?
As far as the timing belt,if it has been on the car 7 yearsor 75,000 miles, you just install a new water pump,belt &all the pulleys & tensioners in one kit,after you check cylinderintegrity,valves,compression & suchA cylinder contribution test is done first with an oscilloscope& software to do that.Once the above mechanical condition of the motor isout of the issue, you move on to other testsSmoke testing for vacuum leaks,fuel & spark issues,etc.Can you check timing belt-- if fairly new,yesYou can put a camera wand behind any dust cover& you can use your scope software again to look at cam,crank,injector & spark events in relation to when they should happenNow the problem ! To find a shop that has that knowledge,equipment and skill level,not many do.All your mentioned parts can & should also be componenttested, in the proper sequence, if necessaryWhat can you doYou can try & get access to check the timing beltUsing a timing light,no,scan tool to look at data yesYou can test some,a few items, maybe,yourself ifyou Google & study up some on how to do itYou Tube Video is a place you should spend sometime on any subject