problem with truck

[lamar]

I have a 98 GMC with 38000 miles It's rattling and pinging on take off and during driving between 1500 rpm and 2000 rpm Its has a little rough idle in a sequence I'v replaced the plugs,wires the cap seems to be fine. new fuel filter air filter ok no codes are showing and a slite hesitation at take off and acceleration at 35 mph and have tryed higher octane fuels with no change the dealer is saying theres nothing they can do that cold air entering the engine is the problem ya got me ! is this something someone can help me with.thank you

 

[DFulmer]

Lamar - A little more information on the engine would be helpful, but I would recommend checking the fuel pressure (Vortec engines should run about 60-65psi) and cleaning the throttle body and IAC passages.

 

[phasers]

I know this is late, but did you try looking at the EGR circuit? Malfunctioning EGR's (the pintle gets stuck, bent, choked with carbon etc....) can cause the symptoms you described.

phasers

 

Heya. I think I know exactly what your problem is. There could have been carbon build up on your valves and a piece entered your combustion chamber. What happens is that carbon heats up and can ignite the fuel before the plug does. I think this is called pre-ignition. Remember, I'm in high school learning about this stuff and my teacher just got thru explaing all about this "pre-ignition" thing. Just a thought...