Hey guy's the throttle position sensor have been failing and you are unable to pull a code unless it is active. On a throttle position sensor closed throttle=0.0 volts to 5.0 volts @ wide open. If between zero and 5 volts when you operate the throttle if there is a bad spot in between, It will cause a stumbling condition and it is not uncommon. Try disconnecting the battery cables for at least 1/2 hour to clear KAM {keep alive memory} reconnect and start your engine and let it idle at least 15 min. the computor will relearn in that time. It is very important to do that last step! do this any time you replace a part that is in question and pulls a code. Try this and if your problem goes away for a bit and comes back try testing t/p sensor or see if it pulled a code at this time, good luck guy's.