Silverado runs rough when engine is warm

Tiny
BOMBER2782
  • CHEVROLET SILVERADO

I have a 99 silverado, 5.3 liter 4x4 137k miles. Runs great when engine is cold. After about 10-15 minutes of driving when engine warms up, engine bogs down, idles rough, and dies when throttle is applied. I ran the codes, had low voltage x4 oxygen sensors, and random misfires. I replaced the 02 sensors because I am well over 100k miles. I also replaced the plugs (gapped to.060), wires, flushed the fuel system, new fuel filter, put in Shell 91 octane, replaced gas cap (the o ring was cracked badly). Still no fix. I have heard it might be the MAF, MAP, TPS, intake gasket leak. Any suggestions? I'm a full time student and broke as hell. I cant afford to have it fixed at a shop. What is wrong? Any ideas will help! This truck is nothing but problems! :X :x :x

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Sunday, February 12th, 2006 AT 6:01 PM

20 Replies

Tiny
CHEVY350GUY
  • MEMBER

Start by checking the MAF

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Sunday, February 12th, 2006 AT 7:32 PM
Tiny
BOMBER2782
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If its the MAF will it set a code?

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Monday, February 13th, 2006 AT 5:48 PM
Tiny
CHEVY350GUY
  • MEMBER

It may but it may not. It depends how far the sensor is out of range. But because it happens after it warms up I would start there.

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Monday, February 13th, 2006 AT 5:59 PM
Tiny
BOMBER2782
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I replaced the MAF sensor. The "service engine soon" light went out. I let it warm up to about 200 degrees or so, drove it for about 15 minutes and it was driving a lot better than before. The light came back on though, 'system too lean, bank 1.' It only seems to do this when I give it a lot of throttle. I put some fuel system cleaner in the fuel when this whole thign started last week, you think this might be causing it to be sluggish? Or what about another fuel filter, or even fuel pump? Are there more advanced ways of diagnosing this truck sinece there are no codes if I take it into a shop? I thought I would save money by doign it this way, but I have spent about $400 so far, and its still not fixed. Thanks- Eric.

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Tuesday, February 14th, 2006 AT 10:28 AM
Tiny
CHEVY350GUY
  • MEMBER

This should be hooked up to a scanner so you can see live data as it happens to better diagnose the problem. Before throwing more money at it.

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Wednesday, February 15th, 2006 AT 6:28 PM
Tiny
BOMBER2782
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Do you have any idea how much a shop might charge me for something like that?

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Wednesday, February 15th, 2006 AT 11:04 PM
Tiny
WINDDILLA
  • MEMBER

I have a 99 Silverado 5.3 as well. I recently had it in the shop to have them check a couple of diagnostic trouble codes and was charged $84. (North Dallas)

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Friday, February 17th, 2006 AT 3:06 AM
Tiny
BOMBER2782
  • MEMBER

I tested the fuel pressure tonight. I get 18-20psi with the key on-off a few times. When running I get between 15-22psi. What next, new fuel pump or regulator? Thanks, Eric.

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Friday, February 17th, 2006 AT 9:49 PM
Tiny
WINDDILLA
  • MEMBER

Have you cleaned the inside of the intake port on your throttle body?

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Saturday, February 18th, 2006 AT 1:43 PM
Tiny
WINDDILLA
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Pressure is definitely low. Should be about 60 psi I think. Low pressure points to fuel pump rather than regulator. Can you hear the pump whine when you turn the key over without starting engine?

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Saturday, February 18th, 2006 AT 1:57 PM

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