07 Silverado Classic Shudder At Idle.

[mbritnell]

The truck is a 2007 Silverado Z71 Classic, 77,000 miles, with 5.3l flex fuel and after warm up it has what seems like a miss fire or shudder. It doesnt do it when cold and I dont have a check engine light. It has progressively gotten worse in the last 10,000 or so miles. Before I go and change the plugs I was wondering what it could be. Thanks in advance.

[mbritnell]

Well this morning I cleaned the MAF and the throttle body and now have a additional problem. The truck now idles up higher than it used to at start up, no matter whether it is cold or at normal operating temp. Then after a few seconds it sharply falls back to normal rpm. Then when coming to a stop while driving it revs up enough for me to have to apply the brakes harder than usual and then once stopped the idle returns to normal. Please tell me what I did wrong.

[Nytemare]

Could be your O2 sensors going out...they give a little stumble (usually the forward ones) before they throw a code.

 

My money would be on a dirty MAF if you haven't already cleaned it...which would make sense with it not doing it cold.

[mbritnell]

Thanks for the quick response. If it is a dirty MAF, what is the best way to clean one?

[Nytemare]

Thanks for the quick response. If it is a dirty MAF, what is the best way to clean one?

MAF Cleaner....spray it in from both sides...really good, set it aside and let it dry, than put it back in.

 

I've used this one with good luck....

http://www.crc-canada.ca/Default.aspx?tabid=235

[mbritnell]

Thanks again for the help. I will clean it tomorrow and report back.

[Nytemare]

Thanks again for the help. I will clean it tomorrow and report back.

Its a cheap fix...and something easy to start with right...yeah get back with results...

after this I would clean the intake manifold internals and Throttle body...you can do this with a product called Seafoam, or you can bring it to the dealership, they have a tool to clean it. Seafoam is like 12 bucks a can....dealer is like 120 for the service....but its a very good service. Another thing you can do also if you haven't done it in a while, run a tank of fuel with some injector cleaner...like techron...in it.

[mbritnell]

I have used the sea foam before but not in this truck.

As far as the injector cleaner, I usually run the Lucas injector cleaner every oil change. I dont know if it does any good or not though.

[Nytemare]

I have used the sea foam before but not in this truck.

As far as the injector cleaner, I usually run the Lucas injector cleaner every oil change. I dont know if it does any good or not though.

I use the same stuff....have for 7 years now...on several vehicles...its never let me down. On a friends Blazer (4.3) the injectors were so gummed up it would die in the driveway. We tosses a small bottle in with about 5 liters of fuel and just let it run there...with in about 30 seconds it ran noticeably better...after a quick drive on the highway we tossed a new tank of fuel in it, it hasn't stalled after. We than used a can of TB cleaner on it to make sure everything else was clean too...would have Seafoamed it....but nowhere I am from sold Seafoam than...they do now though.

 

That's proof enough for me that it works.

But yeah...maybe a little Seafoam in the intake will help smooth everything out too.

[jro909]

my 04 5.3 with 110k on it has what it feels like is a misfire or shutter, no lights or codes at all...somebody told me its the ethanol they put in gas now a days...i'm going to try my mechanical shrink's(nytemare lol) hes rather well versed in GMTs

[Nytemare]

Well this morning I cleaned the MAF and the throttle body and now have a additional problem. The truck now idles up higher than it used to at start up, no matter whether it is cold or at normal operating temp. Then after a few seconds it sharply falls back to normal rpm. Then when coming to a stop while driving it revs up enough for me to have to apply the brakes harder than usual and then once stopped the idle returns to normal. Please tell me what I did wrong.

Did you make sure things were good and dry??

The ECM is just re-learning the MAF readings and adjusting fuel trim...you likely will have to get it into closed loop mode...usually 15 min on the highway at 60-70MPH will do this or it should settle out in about 25 miles or so.