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So recently I've been experiencing when starting my car and taking off, before I pull out on the street, it dies out or the RPM goes down and then back up. I put some Seafoam in the gas tank and even in the engine oil hoping it would help. Not much has changed. I even noticed that when I was driving and putting the pedal down, it felt like I was forcing it, but still went. Finally, the engine light came on and it gave P0121 Throttle/Pedal position sensor A circuit range/performance. I'm new to all this and have been watching videos and reading forums, but this is a major thing for me. I'm eager but scared to do it, lol. Do I clean it first, hoping that is all it needs, or does it need to be completely replaced? I also had rats in the engine area, but was able to deal with that issue. I even though that maybe the rat did something, but I don't see any signs on the wires. Please provide some kind of feedback.
 

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You maybe able to clean the throttle body and fix your issue. Make sure to disconnect the battery and unplug the throttle body to make sure you do not have power to the throttle body while cleaning. The best way is to remove the throttle body. Pull the intake off, and there are 4 bolt for the throttle body. Clean it put back on.
 
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You may be quite surprised what you find when you look at the throttle body. When I bought my Cobalt, there was a lot of oil and carbon built up. I used the Seafoam induction cleaner. Has a straw that goes into the throttle body and then the intake pipe and boot is reattached over it. Then it’s sprayed with the engine running at about 2500 rpm I believe. Worked good in my case. But it dirtied up the spark plugs, so ended up removing them and cleaning with brake cleaner once the engine was cold from sitting over night.

Two months ago I had a Tahoe with the pedal position code. I replaced the accelerator pedal assembly to fix it. It is similar to the Cobalt. But I would try cleaning the throttle body first. The pedal does go bad sometimes though since it an electrical part.
 

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Not sure what year and model you have but pretty sure all of them are electric pedal to throttle body, no cable. So if you had to push the pedal harder than usual, either the carpet is in the way, pedal bolts loose, etc, or the pedal is bad. Never hurts to clean the throttle body anyway.
 

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I believe all of the Cobalts have the electronic throttle body. The Ions had the first 2-3 years with a cable TB.

It really could be carpet, debris, or even the spring inside the pedal assembly that could cause a harder than usual pedal. Although I’ve never run into one that had the hard pedal problem. Usually when I’ve had to replace them, they have become loose, or broken. And most commonly have a dead spot in them that causes the vehicle to go into limp mode or reduced engine power.
 

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My 2010 Cobalt had this problem report twice, but it goes away after a few minutes with the engine off before restarting the engine. It reports the A position sensor error. There are 2 sensors on the throttle, an A and a B. The A sensor is accualy used but both have to agree or the engine runs verrrry rough. I assume the B sensor is there to prevent runaway acceleration.
 
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