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2011 Malibu LT 2.4L - "Malbu"
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Discussion Starter · #1 ·
2011 Malibu LT, 2.4L L4, 6 Speed, 186,000-187,000 Miles
Code P0121


I've had this car since March, and at 186,000 miles it's doing very well.

However, over the last few months I have noticed that giving the vehicle light throttle after not completely stopping does nothing for about 5 seconds. I've hated this, but gotten used to it.
Today I gave the car like 5/8 throttle and 2 minutes later the check engine light came on. Later that day I took it to AutoZone and scanned it, and got code P0121. I then scanned it at a friend's house with a pretty good scanner. After scanning, the check engine light disappeared.

I have done a small bit of research and could not find any solid evidence of my exact problem. Some say "replace the throttle body" and others say "replace the whole pedal."

Also, the "malbu" has not gone into "failsafe mode." It can still give all the power it's got.

I really need help. I love this car and I want it in good shape.
 

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|P0121 CHEVROLET code possible causes

  • Faulty Throttle Position Sensor
  • Throttle Position Sensor harness is open or shorted
  • Throttle Position Sensor circuit poor electrical connection
  • Faulty Engine Control Module (ECM)
Throttle body. Pedal assy. is a different code.
 
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2011 Malibu LT 2.4L - "Malbu"
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Discussion Starter · #3 ·
|P0121 CHEVROLET code possible causes

  • Faulty Throttle Position Sensor
  • Throttle Position Sensor harness is open or shorted
  • Throttle Position Sensor circuit poor electrical connection
  • Faulty Engine Control Module (ECM)
Throttle body. Pedal assy. is a different code.
So, what do you suggest I do to pinpoint the problem? Or should I replace the throttle body since the TPS is built into it?
 

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I myself would replace the throttle body as it set a hard code. Your could try unplugging / plugin it's connector but it is probably worn and when they start to fail they can be erratic.
TPS moves every time the the gas pedal moves. That's a lot of movement. Highest wear in it would be just of idle.
 

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Discussion Starter · #5 ·
I myself would replace the throttle body as it set a hard code. Your could try unplugging / plugin it's connector but it is probably worn and when they start to fail they can be erratic.
TPS moves every time the the gas pedal moves. That's a lot of movement. Highest wear in it would be just of idle.
Thank you, I'll check the connector first and then see about ordering a new throttle body Thursday. I won't be able to work on it til then. I'll get back and let ya know if it fixed my issue.
 

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Discussion Starter · #6 ·
I myself would replace the throttle body as it set a hard code. Your could try unplugging / plugin it's connector but it is probably worn and when they start to fail they can be erratic.
TPS moves every time the the gas pedal moves. That's a lot of movement. Highest wear in it would be just of idle.
I am going to go purchase a throttle body in a couple hours, my local parts store has one in stock. (sure hope it comes with a gasket!)
I'm aware I will have to do an idle relearn procedure after replacing it, and to my understanding, it's very simple. I just want to make sure this is correct.

Step 1: Start the car and let it idle for 3 minutes. Idle will likely be high.
Step 2: Turn the car off for 1 minute.
Step 3: Restart the car for another 3 minutes. Idle should be normal.

If idle is not normal after Step 3, drive above 45 mph and do acceleration/deceleration cycles. Afterwards, let the car idle for 5 minutes.

If it is still not idling normally, restart the process.

Is this the correct procedure?

If so, what do I do if it still does not relearn the idle?
Thanks in advance.
 

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2011 Malibu LT 2.4L - "Malbu"
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Discussion Starter · #7 ·
I myself would replace the throttle body as it set a hard code. Your could try unplugging / plugin it's connector but it is probably worn and when they start to fail they can be erratic.
TPS moves every time the the gas pedal moves. That's a lot of movement. Highest wear in it would be just of idle.
I replaced the throttle body. Went thru relearn procedure. Car idles at 3500-3600 RPMs. I've tried disconnecting the battery cables and resetting it by touching the ends together. Nothing. At idle, brakes can not hold the car stopped while in gear. Going down the road, the lowest RPMs I saw was 1400. I need help. Going to try and find a nearby shop that might be able to set my idle with their fancy computers.

Also, the car accelerates just fine. I'm sure I put the engine cover on correctly, but I will take it back off tomorrow and make sure that the intake is sealed completely to the throttle body.
 

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Aftermarket or reman. part ? That may be the issue with it not relearning.

Without Scan Tool-Learn

Important:
Do NOT perform the Without Scan Tool-Learn procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: A L L Diagnostic Trouble Codes ( DTC )\Testing and Inspection\Diagnostic Trouble Code Descriptions).

  1. The engine speed is between 450-4,000 RPM.
  2. The manifold absolute pressure (MAP) is greater than 5 kPa.
  3. The mass air flow (MAF) is greater than 2 g/s.
  4. The ignition 1 voltage is greater than 10 volts.
  5. Start and idle the engine in Park for 3 minutes.
  6. With a scan tool, monitor desired and actual RPM.
  7. The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
  8. Ignition OFF for 60 seconds.
  9. Start and idle the engine in Park for 3 minutes.
Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.

  1. After the 3 minute run time the engine should be idling normal.
¤If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.
  1. After the drive cycle, the engine should be idling normally.
¤If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.
  1. Once the engine speed has returned to normal, clear DTCs.
 

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Discussion Starter · #9 ·
Aftermarket or reman. part ? That may be the issue with it not relearning.

Without Scan Tool-Learn

Important:
Do NOT perform the Without Scan Tool-Learn procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: A L L Diagnostic Trouble Codes ( DTC )\Testing and Inspection\Diagnostic Trouble Code Descriptions).

  1. The engine speed is between 450-4,000 RPM.
  2. The manifold absolute pressure (MAP) is greater than 5 kPa.
  3. The mass air flow (MAF) is greater than 2 g/s.
  4. The ignition 1 voltage is greater than 10 volts.
  5. Start and idle the engine in Park for 3 minutes.
  6. With a scan tool, monitor desired and actual RPM.
  7. The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
  8. Ignition OFF for 60 seconds.
  9. Start and idle the engine in Park for 3 minutes.
Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.

  1. After the 3 minute run time the engine should be idling normal.

¤If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

  1. After the drive cycle, the engine should be idling normally.

¤If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.

  1. Once the engine speed has returned to normal, clear DTCs.
So in order for it to learn I have to have a scan tool plugged in and clear the codes.

It is an aftermarket TB. Bosch brand. Picked it up from O'Reilly's.

Also my friend's uncle printed out a paper for me that tells me an ECU accelerator pedal reset procedure, a pedal release position learning procedure, a throttle valve closed position learning procedure, and an idle air volume learning procedure (throttle position learning.)

Basically recalibrating the throttle body.
Also posting a picture of the old throttle body... Incredibly dirty.
Automotive tire Motor vehicle Gas Automotive wheel system Machine

Those little lines are from me gathering some of the carbon off of it with a screwdriver.
 

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2011 Malibu LT 2.4L - "Malbu"
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Discussion Starter · #10 · (Edited)
Aftermarket or reman. part ? That may be the issue with it not relearning.

Without Scan Tool-Learn

Important:
Do NOT perform the Without Scan Tool-Learn procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: A L L Diagnostic Trouble Codes ( DTC )\Testing and Inspection\Diagnostic Trouble Code Descriptions).

  1. The engine speed is between 450-4,000 RPM.
  2. The manifold absolute pressure (MAP) is greater than 5 kPa.
  3. The mass air flow (MAF) is greater than 2 g/s.
  4. The ignition 1 voltage is greater than 10 volts.
  5. Start and idle the engine in Park for 3 minutes.
  6. With a scan tool, monitor desired and actual RPM.
  7. The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
  8. Ignition OFF for 60 seconds.
  9. Start and idle the engine in Park for 3 minutes.
Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.

  1. After the 3 minute run time the engine should be idling normal.

¤If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

  1. After the drive cycle, the engine should be idling normally.

¤If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.

  1. Once the engine speed has returned to normal, clear DTCs.
This was not successful. Driven the car 20+ miles to no avail. I'm going to try and get it in a shop and let a professional do it.

EDIT: I am taking it to a shop on Monday, they will calibrate the idle with tools.
 

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Might need to take a look at the wiring itself. Rather than me trying to explain it, look up South Main Auto LLC on YouTube...Eric is awesome when it comes to showing how to diagnose faulty wires/grounds. With that many miles on the vehicle, that in itself could be causing a problem based on what the code is and the throttle body did not fix it. Also, using Throttle Body cleaner along with some rubbing compound and you can have your old throttle body looking much better in no time at all.
 

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Discussion Starter · #12 ·
Might need to take a look at the wiring itself. Rather than me trying to explain it, look up South Main Auto LLC on YouTube...Eric is awesome when it comes to showing how to diagnose faulty wires/grounds. With that many miles on the vehicle, that in itself could be causing a problem based on what the code is and the throttle body did not fix it. Also, using Throttle Body cleaner along with some rubbing compound and you can have your old throttle body looking much better in no time at all.
The p0121 code is gone, now I just have P0507- high idle. Obviously high idle. I need a professional to set my idle as the car isn't learning itself.
 

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Discussion Starter · #13 ·
I had my friend's old dad fix my car for me. We basically took the old throttle body and tested it with a meter, it is still working just fine. We cleaned it and put it back on. Now the car is close to idling normally. When I stop in Drive, it takes it about 2-3 seconds for the idle to start dropping from 1000-1100 RPMs to its normal 750 area. When I want to put it in park, I have to wait for the RPMs to drop below 1000 or it will jump to 1500. However if I put it in park below 1000 RPMs it will very quickly drop to 750. The first time this happened I had thought the engine died, it was incredibly quiet.
Unfortunately, at the moment, if you even barely tap the gas while in park, it will jump up to 1500 RPMs. Confusing, but I'll deal with it. I'm guessing the car will learn over time.
 
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