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peterpete190, Auto Technician
Category: Subaru
Satisfied Customers: 29116
Experience:  Auto repair Technician with 17 years experience.Past ASE and other certifications.
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Osmond, My 2006 subaru legacy has a rough idle in the cold

Customer Question

Customer: Osmond, My 2006 subaru legacy has a rough idle in the cold which affects the electrical system( lights, fans). It goes away once the car is at temperature I changed wires, plugs cleaned Mass air flow sensor, cleaned pcv valve and just tested my alterantor and it is reading 14.5 -14. 7
JA: Thanks. Can you give me any more details about your issue?
Customer: It does not throw a code I also replaced the engine temp sensor and put sea foam in to clean the engine. Still same problem
JA: OK got it. Last thing — Subaru Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: Subaru
Expert:  peterpete190 replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Since there is an electrical fault with the rough idle and is most affected when cold or in the cold this sounds like a possible electrical connection fault causing this here.Inspect the battery cables for any issues and if any issues are found this will need corrected.If the cables are corroded they will need cleaned and if they are damaged they will need replaced.If these are or were already checked and found o.k. let me know so we can continue.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
I verified the cables are clean and undamaged.
Expert:  peterpete190 replied 1 year ago.

Can you tell me how the electronics are acting up on your vehicle here,what they are doing when this occurs?

Customer: replied 1 year ago.
It only happens when i start the car. It is worse in the cold. The idle is "missing" every so often and when it does, it affects the lights as they dim. Once the car is warmed up, I have no issue.
I cleaned the ground wires and it still did it. I also tried some belt dressing on the altenator belt and that appears to have had an affect. I will know for sure later today when I start the car up as it is cold here.
Expert:  peterpete190 replied 1 year ago.

If the belt was slipping around the alternator this can cause this type of fault here and the cold will affect the belt from gripping on the alternator properly.I have had to replace the belt before when it was worn slipping like this here.If you applied belt dressing and this helped the issue here this may be the case and the belt may need replaced to correct this fault.I would check and see if this is the cause here as well as make sure the alternator connections are clean and tight.

I would have the alternator tested as well as even though it is putting out voltage the amperage from it may be weak when cold causing this here and it may need replaced.

Thanks Pete

Customer: replied 1 year ago.
It happened again today despite the belt dressing. Other than the alternator, could there be another cause
I will follow through to test the amps
Expert:  peterpete190 replied 1 year ago.

It sounds like an electrical fault here.I would have the amperage tested from the alternator and maybe check for any loose or damaged battery cables at the battery or alternator and starter.Check for any loose or damaged wiring for this fault.

Thanks Pete

Customer: replied 1 year ago.
I went and started the car, put the voltometer on it, had my wife turn on the air conditioner, high beams, radio and the voltage stayed the same, no drop so I assume the amps are fine.Any other thoughts.
Expert:  peterpete190 replied 1 year ago.

This is a tough one for me to answer fully myself.I will have to open your question up for others here to see if anyone else can assist further.I hope you can get this resolved with ease.

Thanks Pete

Customer: replied 1 year ago.
Pete:Have you heard from anyone else about what may be causing my issue?