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Jay
Jay, Chevy Mechanic
Category: Chevy
Satisfied Customers: 594
Experience:  5 yrs experience, GM Trained,
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Chevrolet Cobalt LS Where is the throttle positioning sensor

Customer Question

Where is the throttle positioning sensor of my 2005 Chevy Coblat LS. If this a do it yourself job or 500.00 at the mechanic?
Submitted: 3 years ago.
Category: Chevy
Expert:  Jay replied 3 years ago.
Do you have a check engine light on and is the engine missing?
Customer: replied 3 years ago.
Yes, the engine light is on steady. No, it does not seem to be missing. It just idles rough when I come to a stop, and sometimes will stall. It starts right up again though. The code that came up was P0178, if that helps any?
Expert:  JHoop replied 3 years ago.
Hello , my name isXXXXX you for choosing justanswer.com.

Are you sure about the code PO178 as that is not a code in any of my databases?
Customer: replied 3 years ago.
No, I am not sure, I have it written down at home and I am out of town until tonite. Are you Jay?
Expert:  JHoop replied 3 years ago.
No, I am a new expert. I can help you if you supply the correct code here. I will keep your question open. You can get back to me anytime answering any e-mail sent to you related to this question or by logging into your JA account. Thanks again, JHoop
Customer: replied 3 years ago.
Will do. Thanks.
Expert:  JHoop replied 3 years ago.
Great. Have a nice day, JHoop
Expert:  Jay replied 3 years ago.
Hello,Customer this is Jay, JHoop is correct in that code P0178 does not exist, therefore you may have made a mistake in writing the code down or in your memory. Please check again and repost. In just what you are mentioning it may be a catalytic converter issue, but I don't want to jump to any conclusions. Let's wait till we have the correct code. Thanks.
Customer: replied 3 years ago.
The codes are P0171 and P0128
Expert:  Jay replied 3 years ago.
O.k. That helps more! P0128 is likely being caused by a faulty thermostat, so your best bet would be to change the thermostat. P0171 is a lean condition get an appropriate cleaner such as brake clean and spray out the MAF sensor. Also make sure there are no intake leaks such as the air intake not hooked up properly. Do you use an oiled air filter? Please reply if this does not help, thanks! Feel free to reply to the air filter question.
Jay, Chevy Mechanic
Category: Chevy
Satisfied Customers: 594
Experience: 5 yrs experience, GM Trained,
Jay and 6 other Chevy Specialists are ready to help you
Customer: replied 3 years ago.
What is the MAF sensor and where is it located? I just recently changed the air filter and had a hell of a time replacing the cover. The light came on a couple of days after that, so maybe I didn't seat the cover properly. I don't use an oiled filter. I just put it in right out of the box. The problem with the rough idle and stalling started a few weeks before and the engine light had not come on. My original question was about the throttle positioning sensor? Would a faulty one cause the rough idle and stalling problem?
Expert:  Jay replied 3 years ago.
I don't think your throttle position sensor is the problem because you would likely have other issues and codes. The MAF sensor is located just past the air filter in the air intake stream so my guess is that you didn't seal the air filter box. Once you have replaced the thermostat and sealed the air box please report and let me know how it is running.
Customer: replied 3 years ago.
Is it attached to the wiring harness just past the air cleaner? Should I clean or replace the sensor as well?
Expert:  Jay replied 3 years ago.
Yes it is just past the air cleaner. It measures air flow and is inline with air intake.
Customer: replied 3 years ago.
Thanks. I'll try it.
Expert:  Jay replied 3 years ago.
Remember, please reply after you have done these things and let me know how it is working. If it has not fixed it then we'll continue to figure it out.
Customer: replied 3 years ago.
Hi Jay,

I cleaned the sensor, checked the air cleaner cover and it seems to have improved the idle. I don't think the thermostat is malfunctioning though since my heat works well. I reset the engine light and it stayed off for 2 weeks. When it came back on, the only code was P0128. Anti-freeze level is fine. I may try changing the ECT sensor when I get a chance.
Expert:  Jay replied 3 years ago.
O.k., although I'll let you know that in my experience a P0128 code usually is related to a thermostat that is not working correctly. Thanks.
Customer: replied 3 years ago.
Is the thermostat something that I could replace on my own or should I leave it to the pro's?
Expert:  Jay replied 3 years ago.
Thermostat on these is a touch difficult and perhaps would be best to take it into a shop to get it done, Please reply if you have any questions, thanks.
Customer: replied 3 years ago.
Just letting you know, I had the thermostat and sensor replaced and the problem is solved.

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