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Rough idle on 2001 Silverado when starting up in morning..

Customer Question
Rough idle on 2001...

Rough idle on 2001 Silverado when starting up in morning.. Lasts about 2 mins... Come back 15 mins later starts/runs fine.. No other problems other than when sitting overnight. I checked for intake manifold gaskets for leaks-- none. Changed bank 1 #1 o2 sensor.. MAF sensor cleaned out.. I can let truck sit all day, starts & runs good.. Only problem when sitting overnight... Temp in morning or 12 hours later are the same.. Any ideas?

Mechanic's Assistant: Have you located all of the vehicle's oxygen sensors? Are the wires leading to and from each intact and in good shape?

Changed out Bank 1 sensor 1 new sensor.. Did not change out any other ones... When problem occurs, no codes are dropped... Just the rough idling for a couple mins. then runs perfect...

Mechanic's Assistant: Are you fixing your MINI yourself? What have you tried so far?

This is a Chevy 5.3l Silverado 4X4.. I had it at a chevy dealer, they THINK it is a intake manifold gasket... I tried with the spraying of brake clean on the intake gaskets when starting up.. No change in the running of it, so, I can't really go with the gasket problem.. I am looking for a definite answer, NOT a guess it is this or that....

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No just what the heck is causing this... Thank you....

Submitted: 6 months ago.Category: Chevy
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Answered in 10 minutes by:
12/24/2017
Chevy Mechanic: Lou P., ASE Certified Technician replied 6 months ago
Lou P.
Lou P., ASE Certified Technician
Category: Chevy
Satisfied Customers: 6,089
Experience: Building and driving Chevy's since I was in the womb!!!! Camaro and Corvette enthusiast, access to factory diagrams and tsb's
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Hello my name is***** am going over your request now and will reply back soon with some info OR a few questions that would help me better determine how to help you. Keep in mind I have no idea of your technical ability or what you do and do not already know. So the more info you can tell me the better. I have been on the site for almost ten years and have oustanding 5 star ratings so trust that I will do everything I can to get you taken care of, Lou
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Chevy Mechanic: Lou P., ASE Certified Technician replied 6 months ago
It did sound like intake gaskets or a manifold leak to me . Since you already checked that the next thing would be fuel pressure. Leave a gauge on overnight and see if pressure jumps to 60psi or more with first key turn. That is where i would start. Lou
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Customer reply replied 6 months ago
why does it only do it in the morning? Truck can sit there for the next 10 hours & have no problem?
Chevy Mechanic: Lou P., ASE Certified Technician replied 6 months ago

fuel pressure test will rule out fuel pump

it can bleed down overnight and cavitate

is there a huge temp differance in your area? from night to morning?

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Customer reply replied 6 months ago
If it bleeds down overnight it will bleed down 10 hours later.. Temps have been within 5 degrees night/or day.. Today different due to snow... But problem was there with a +/- 5 degree swing.. I don't want to look at a head gasket problem & find out it wasn't the problem.. Big $$$$....
Chevy Mechanic: Lou P., ASE Certified Technician replied 6 months ago

lol, ok , i can see you dont want to follow my advice, i will opt out.

best wishes,

Lou

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Customer reply replied 6 months ago
It seems you don't agree with my logic either.... Thank you for your time.....
Chevy Mechanic: david craig, Auto Mechanic replied 6 months ago
david craig
david craig, Auto Mechanic
Category: Chevy
Satisfied Customers: 5,778
Experience: owner/mechanic at 3D Automotive
Verified

you have sticky valves. run a can of seafoam in the intake and gas tank. problem solved.

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Chevy Mechanic: david craig, Auto Mechanic replied 6 months ago

hows it going?

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Chevy Mechanic: david craig, Auto Mechanic replied 6 months ago

do you still need help?

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Customer reply replied 6 months ago
We fixed our problem(not valves).. My neighbor found the problem... Thank you for your help...
Chevy Mechanic: david craig, Auto Mechanic replied 6 months ago

very glad to hear

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