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Q: High idle in the morning and after sitting for 5+ hours

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When I start my truck in the morning, normal warm temperatures, the RPMs shoot up to 2500 and drops down to 1500-1800 and just fluctuates for about 10 seconds. Then the truck shakes a bit.

I went to a dealership that diagnosed no issues. No lights on or anything. They basically said they found large amount of carbon build up in the throttle body (which at 45k, I'm not sure if that's accurate). So they cleaned the throttle body and fuel system. Also they performed idle relearn and fuel composition relearn.

I've had my truck back about a week and it started fluctuating again. It was good for about a week.

So I'm skeptical to take it to another Chevy dealer or shop cause this shop couldn't find the issue. They just did something they thought would fix the issue.

Please help as I don't have much cash and I've wasted $200 on that useless trip to the dealership already.

Thanks!

My car has 45000 miles.
My car has an automatic transmission.

A: Hi, thanks for writing in. I’d like to star...

Hi, thanks for writing in. I’d like to start by saying, you haven’t wasted your money. Even if your issue hasn’t been repaired, they did some quality maintenance that will help your truck last many more miles. I understand your frustration with this though. You went there for an issue that wasn’t taken car of.

I want to offer you another perspective about this. This may be a change to what you are used to with your truck, but the reality is it really isn’t a problem that does anything but create a higher idle than you are used to. I am certain something has changed, but determining what small change has occurred in a complicated system will most often take a lot of time to figure out. More time equals more money. More money for an issue that doesn’t seem to create a problem. So you need to decide, is it worth the money to figure out why this change has occurred?

As a technician, with my own car, I can tell when something has changed, but often it is too early to determine exactly what it was. I will often wait until the symptom becomes pronounced enough to easily figure out. I have that issue with my front end at this moment. It began to wonder slightly more on the highway. But chasing the problem now will likely lead to an inconclusive diagnosis. I will wait a bit longer until the play becomes more pronounced and I will know for sure. I would suggest that this method may be the most cost effective and least frustrating path. The alternative is hoping you have found a technician that has experienced your issue and has successfully found the source. Otherwise, you are likely to have the same experience.

If I were tasked to work on your car regardless, I would first smoke machine your motor looking for cold vacuum leaks while I had a scanner connected and monitoring all scan data. Even so, this may or may not reveal the source of the change.

If you would like a technician from YourMechanic take a crack at this, I recommend the following inspection: Engine idle speed is high inspection

Be sure to send the technician a note explaining this is a start up only condition.

Good luck!

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