What would cause the idle to drop to the point of cutting off? Would that be the throttle position sensor or what?

Do you have any trouble codes?

check for vacuum leaks!

I have to ask the basics, how long since a tune-up, any applicable trouble codes?
Cleaning the throttle body and idle air control may help?
One thought is to unplug maf sensor, start vehicle, if idle is now normal, you found the problem. Could be wiring circuit--connector or maf sensor.
There might be a vacuum leak causing a problem? If fuel trim is high at idle, but, returns to normal under load, it's usually a vacuum leak.

If check engine light is on get the codes. The best that can be done is a guess without them my best guess would be idle air control motor (IAC).

In most cases as mentioned above the IAC can contribute but in your case sounds like your Throttle Control Position Sensor Switch eith er has a bad connection or the switch is bad all together. they are betwen 25 and 40 dollars any parts store stocks it.

There are 2 relays in the relay box that could cause this problem the EEC relay and the FUEL pump relay the best test for EEC relay back probe the throttle position sensor for the 5 volts reference signal run engine and watch to see if you lose this voltage. and fuel pump relay install a fuel pressure gauge to fuel rail service port and check to see if pressure drops to zero.

Try cleaning the idle air sensor on the side of the throttle body can be a cause for headaches.

Hello! The problem is more than likely being caused by the Manifold Absolute Pressure (MAP) sensor...It is bolted to the side of the throttle body...Has wire colors Gray (+5volts)...Light Green (Signal out)...And Black (Return or Ground)...Using safety pins...Push the point into the rear of the in-place MAP connector...Clip the (+) meter probe, set to read +5volts, to the Light Green wire...The (-) probe to the Black...Start the engine...At idle reading is close to +5 volts...At 2500 rpm reading drops to 1.5-2.0 volts...If you have already replaced the MAP and do not get these results...Pull the MAP connector and read back into it using the same procedure...If, for instance, the Light Green signal lead remains on +5 volts it is probably shorted to the Gray in the harness...No voltage is present; The Gray wire is open...Or, No ground on the Black, the Black is open...Whatever you find wrong...Merely cut out the bad wire and re-connect on both ends..See diagram of MAP location below....Send a comment via e-mail....Guru...Saailer





I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

The drivability issue you describe has a multitude of possible causes. The best advice I can give you is that you take/tow the vehicle to the local/nearest Hyundai Service Department and have it properly diagnosed. Possible causes:
#1. Fuel delivery (Fuel Pump pressure, Injector(s) clogged/leaking)
#2. Vacuum Leak(s)
#3. Faulty Throttle Position Sensor (TPS)
#4. Electrical (Wiring)
#5. Faulty Sensors (Crank Position Sensor, Cam Position Sensor, Idle Speed Control Actuator, Faulty Manifold Absolute Pressure Sensor, etc.)
#6. Contaminated Fuel
#7. Faulty Powertrain Control Module (PCM)
Best advice, get is properly diagnosed.

I faulty Idle Air Control valve (IAC) can cause these specific symptoms. You could try diconnecting the IAC valve (usually near the throttle body) and regulating the idle yourself. If the fluctuations go away and you are able to hold a constant idle position with the gas pedal (if vehicle will start), the IAC is the problem.

yes checked fuel pressure and replaced the fuel filter, checked the mapp sensor,tested throttle position sensor, has strong spark, 50psi fuel pressure, fresh tune up, runs real rich and rough idle but wont rev up like fuel injectors arent speeding up, also checked exhaust. thanks julius