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05 cobalt rpm drops to 500 or under when stopping. Instantly…

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05 cobalt rpm drops to...
05 cobalt rpm drops to 500 or under when stopping. Instantly comes back up but engine tries to chug out and headlights dim when it happens. Has brand new battery.
Submitted: 2 years ago.Category: Chevy
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Answered in 1 minute by:
1/23/2016
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago
JOHN aka Eauto
JOHN aka Eauto, The Car Guy
Category: Chevy
Satisfied Customers: 17,484
Experience: ase tech
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is the engine light on?

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Customer reply replied 2 years ago
Yeah reads an emmisions code
Customer reply replied 2 years ago
New o2 sensors and catalytic converter. Still reads same code
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

what codes? po420?

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Customer reply replied 2 years ago
Not sure, shop just said cat or o2 so I did both
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

can you tell me the current codes? do you have a scan tool? any other warning lights on?

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Customer reply replied 2 years ago
Unfortunately I dont
Customer reply replied 2 years ago
I've read that a dirty throtle body is a common issue.
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

I would start by cleaning the throttle body with throttle body spray and a tooth brush.. I would also clean the mass air flow sensor wit mass air flow cleaning spray ..f no improvement we will need trouble codes,,

The check engine light comes on when the on-board computer detects a fault in engine driveability or performance, transmission control system or transmission, or the emissions system, and a fault code is set and stored in the computer. Faults that can set the check engine light can range from a vaccuum leak, engine mis-fire, low engine compression, faulty sensor such as O2 sensor or other engine sensor, hydraulic pressure loss in transmission, transmission shift solenoid, open/short in wiring harness, emission evaporative system leak, or one of over a hundred different reasons.
The only way to know what set a fault code and turned the check engine light on is to have a diagnostic scanner hooked up to the on-board computer and read it for stored diagnostic fault codes. Many auto parts stores will do this service for free- (like auto zone)check with you local parts stores. If none in your area do, then you will have to take it to a shop and pay to have the computer read for stored fault codes.

Without knowing the fault codes numbers, it would be irresponsible to guess as to the cause as there are hundreds of possible causes

if you provide me a diagnostic code we can narrow down the cause of failure

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Customer reply replied 2 years ago
Ok I will try that first
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

Please remember to only rate my service when you are satisfied. IF you feel the need to rate "Poor Service" or "Bad Service", please stop and reply to me via the REPLY TO EXPERT button with the issue you have. I will be happy to continue further and do everything I can to provide you with the service you seek.

I am not paid unless I get a rating of 3 to 5 Stars/Smiley Faces. If I have helped you with your question, please give me an appropriate rating so that I get credit for helping you

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Customer reply replied 2 years ago
Ok how do we continue this if cleaning the throttle body doesn't work
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

just respond here just like e are doing

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Customer reply replied 2 years ago
Ok so I shouldn't rate and finish yet then?
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

either way you can still respond

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Customer reply replied 2 years ago
Ok thank you
Chevy Mechanic: JOHN aka Eauto, The Car Guy replied 2 years ago

you are welcome

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