02 Tahoe Cold Start Problem

['99 SLP#24]

I have a 2002 Chevrolet Tahoe with the 5.3L Flex fuel motor. Which is a joke since you can't buy E85 in Oklahoma, but that's not the point. The gas mileage has been steadily declining, even for a Tahoe, down to around 12 mpg in town for the past 2-3 months. Last week the Service Engine Soon light came on, I had it scanned at Autozone and they said it was both front O2 sensors and that the engine was running lean. I ran some fuel injector cleaner through the motor and the service engine light turned off almost immediately which seemed a bit quick. Now in the mornings on cold start the motor will drop idle for a brief moment then it will pick back up. As the rpms drop it almost sounds like a miss then as it picks back up the whole truck shakes. This continues but the severity lessens until the truck warms up to operating temperature. It does not affect driving, it only does this when cold and in neutral or park. Once the truck has warmed up it idles as normal and has no problems. What could be causing this?

Short Version: Sounds like a miss during cold start, truck shakes, rpms drop, then goes away once it warms up. Why???

[fspeedster]

Check the fuel regulator. Pull the vaccum line on top if fuel leaks thats the problem.

[02BURBAN]

I Don't Know What Causes That Problme But My O2 Suburban Does Almost The Same But It Will Do It In Drive Also... I Have Used The Diablo To Scan See What The Truck Is Running And I Have Noticed The Front O2 Sensor Running Low And Then They Get Normall After I Run The Truck Hard... But It Only Does When The Truck Frist Starts And As Long As It Stays Running It Drives Normal... When The Cool Front Came By It Stop Doing It... It Is Warming Up In Texas And I Do Not Know If It Will Continue The Same Or Not... Please Post If You Find The Problem...
Thanks...

['99 SLP#24]

Ok well I got tired of trying to figure it out with my limited diagnostic tools. So it's in the shop I'll let you know what they find out.

[02BURBAN]

Ok
Thanks,,

['99 SLP#24]

Intake Manifold Gaskets, they're replacing them today!

[02BURBAN]

Ok I Will Look At Mine ...
Thanks, Angin..

[therommelmann]

Go to this website it will explain all but basically there are estimated to be over 800,000 vehicles that have the same problem
http://www.pistonslap.com/

['99 SLP#24]

Holy old post, I know piston slap is a problem but that's not what was wrong with my truck. It was just the gaskets on the intake manifold. It's been great ever since!