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rough idle when cold outside


idcwmidi

Question

I have a 2003 GMC Sierra with about 117,000 miles that has a rough idle when you first start in the morning. The normal idle is about 600 RPM. When you first start in the morning, it will run at the elevated RPM, but when it starts to drop back down to the normal idle, it will start to run rough and the RPM can drop to about 300 RPM and then jump back up to 1000 RPM. The roughness is more pronounced as the outside temperature gets colder. When this is happening, it will run normal at any elevated RPM so you only notice it at a stop light when you are at idle. At first it started when the temp guage showed about 175 degrees, but smoothed out when it came to full operating temperature. I took this to be at the point that the engine goes from the open loop to the closed loop......which pushed me to it being an intake manifold gasket problem. I checked for any loose hoses and sprayed starting fluid around the edges of the intake manifold and over the hoses but did not get any "surge".......which made me think that maybe it was something else. As it was cheap and easy, I changed out the temp sensor, and as the cooling system was opened, I precautionary changed out the thermostat.......but no change. Althought the throttle body was cleaned about a year ago when the MAF sensor was changed, I cleaned the TB and also removed and sprayed the MAF sensor with MAF cleaner.

I wanted to change out the fuel filter, but I think that it is rusted together with the fuel lines. I have been spraying PB blaster on the connections for the past couple day and will try to separate on my next day off.

 

I ran a bottle of injector cleaner and just refilled the tank with two more bottles, but so far have not noticed any difference.

 

A visual check of the engine does not show any leaking fuel.

 

This past summer, I changed out the spark plugs and spark plug wires.

The MAF sensor is only about a year old.

The fuel pump and fuel pressure regulator are about 2 years old.

 

It is pushing P300, P171 and P174 codes and last night I had a P101 code for the first time.

 

Now, I don't think that both O2 sensors would fail at the same time so I think that those codes are a result and not cause of the codes..... Which takes me back to unmetered air getting into the system after the MAF sensor.

 

I don't know if I should change out the intake manifold gaskets or take it to a shop to get a full scan with data. The gaskets are about $80 which would cover the scan, but am I wasting my time with a bad diagnostic? I would hate to spend the time and money to change out the gaskets and then still have the same problem. Any opinions?

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I'd say get that bad boy to a shop/dealer and get it properly diagnosed. That way the parts being put on are going to fix the problem and not hide the symptoms. That's just my opinion. When my truck threw codes a couple years ago I'm glad I went to the dealer. $1000 parts later my troubles were fixed, fortunately my extended warranty picked up most of it.

 

 

X1000 !!!!

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Both my 2002, 2500 HD Silverado with the 6.0L & my buddy's 2002 GMC Sierra with the 5.3L were having Idle problems with the temperature was down to 15 degrees F or below. Changed both intake gaskets to the more rubust versions and they have run good since.

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I'd say get that bad boy to a shop/dealer and get it properly diagnosed. That way the parts being put on are going to fix the problem and not hide the symptoms. That's just my opinion. When my truck threw codes a couple years ago I'm glad I went to the dealer. $1000 parts later my troubles were fixed, fortunately my extended warranty picked up most of it.

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I have same issue guy at parts store had me replace plugs plug wires MAF sensor all 4 O2 sensors and fuel filter and was in the process of selling me a fuel pump when I realized he was a f*%#ing idiot and why was I listening to him so I got with the good folks on here and turns out it is the intake manifold gaskets bought a set for about 70 bucks took about 4 hours with a couple little girls wanting to help dad accomplices helping out the 5 year old was great help the 7 year old unfortunately was all over the place probably tacked on a half hour to overall project

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