Hello, new to the forum.

My daughter's Elantra was running very sluggish and would hesitate when you stepped on the gas. I had the codes pulled and they were P1127, P0121, and P0707.

I replaced the TPS sensor and that didn't help, so I replaced the MAF sensor and the car ran great for a week. Now it is running even rougher than before and stalling. The codes are (in order): P0121, P0102, and P1127.

I don't know why I'm still getting the P0121 with the new sensor. I found the diagnostic steps for it and I'm getting power and good continuity on the connector side. On the switch side, I get good and even resistance changes as I open the throttle. The RPMs aren't varying wildly, they just don't change right away when you step on the pedal and then the engine suddenly kicks in and they shoot up to where you have the gas pedal.

The MAF Sensor is an A1 Cardone remanufactured unit. The sensor came as a unit with the hose piece and I just replace the entire section in the hose.

I don't know what would cause it to run great for a week and then run worse than before I put the new MAF sensor in it. And why is it still throwing the code for the TPS sensor?

Any ideas on what may be going on?

Thank you in advance for your help!

 

Does anyone have any ideas? Thanks!

 

P1127 = Long term fuel trim multiplicative too rich



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P0121 = Difference between load signal by MAF sensor and load signal calculated by TPS (MAF and TPS are not fault) TP sensor voltage does not agree with MAF sensor

PRIMARY SENSOR:Throttle Position (TP) Sensor

SECONDARY SENSOR(S):Mass Air Flow (MAF) Sensor

SYSTEM(S):Bosch

NORMAL PARAMETERS:TP sensor signals using scan tool with ignition switch on:
a. 6%-13% (250-800 millivolts) with throttle valve at idle
b. Voltage increases as throttle valve opens
c. 95%-100% (4.25-4.8 volts) with throttle valve wide open

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor mounts on the side of the throttle body and is connected to the throttle blade shaft. The TP sensor is a variable resistor (potentiometer) whose resistance changes according to throttle blade shaft position. During acceleration, the TP sensor resistance decreases; during deceleration, the TP sensor resistance increases.
The Engine Control Module (ECM) applies a reference voltage to the TP sensor and then measures the voltage that is present on the TP sensor signal circuit. The ECM uses the TP sensor signal to adjust timing and injector pulse width. The TP sensor signal along with the MAF sensor signal is used by the ECM to calculate engine load.

FAILURE CONDITIONS
The ECM will set a code and the Malfunction Indicator Lamp (MIL) will turn on if the engine load indicated by the Throttle Position (TP) sensor and the Mass Air Flow (MAF) sensor are different by more than 3.5 milliseconds during two back-to-back trips. This code indicates that the throttle position and air flow readings by the TP and MAF sensor, or ECM, do not result in an expected engine load value.
The standard resistance value between terminals 1 and 3 of the throttle position sensor is 1600-2500 ohms.
Engine load is determined by first dividing air flow per crankshaft revolution by the mass air flow sensor hot film constant (constant is based on the number of fuel injectors and injector's mass flow constant). This value is then adjusted by using engine speed and throttle position readings.

SCHEMATIC


TEST PROCEDURE




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P0707 = Range switch - open circuit (replace the switch in the transmission)

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P0102 = Mass air flow circuit low input



1. If the engine stalls occasionally, start the engine and shake the MAF sensor harness. If the engine stalls, check for poor contact at the MAF sensor connector.

2. If the MAF sensor output voltage is other than 0 when the ignition switch is turned on (do not start the engine). Check for the faulty MAF sensor or ECM.

3. If the engine can be idle even if the MAF sensor output voltage is out of specification, check for the following conditions:
a. Disturbed air flow in the MAF sensor, disconnected air duct, and clogged air cleaner filter.
b. Poor combustion in the cylinder, faulty ignition plug, ignition coil, injector, and incorrect comparison.

4. Though no MAF sensor malfunction occurs, check the mounting direction of MAF sensor.

 

First I'd like to say thank you NovaResource for your great response. Now back to the car - I was getting overwhelmed with all of the diagnostic checks in the NR's response and then the very last item hit me, check the direction of the sensor. Well, I'm sure that I installed the tube the same way as the one the I removed. One end of the tube has a screen and I'm sure I put that at the same end as the one I took off. Plus the plug to the sensor fit in exactly the same position as the old one. Anyway, I unhooked the tube with the sensor and flipped it over and there was an arrow! It never occurred to me that it may be directional. The arrow was pointing toward the air cleaner and when I flipped it, it was pointing toward the engine. Well, I reinstalled it the right way and the stalling and hesitation has disappeared!!! I still have the CEL on and I'll go get the codes pulled again, but the car is drivable again.

Thanks again NovaResource for your help!

 

Glad to hear it was something simple.

 

hi i was reading this thread because i have a 2000 hyundai elantra that is doing the same thing and i was looking at your response but i cant see the schematics or test procedures i was wondering if you could please help me

 

Just thought I'd post an update. Unfortunately, the stalling came back and continued. We put it in the shop and it failed the block test, so we had to replace the engine with another used one with 50k on it. Been fine since.