rough running in the morning

[BRZ71]

2003 Silverado Z71 5.3 , no mods except Magnaflow Muffler, not entire exhaust.

55000 miles

 

I have noticed the past couple of weeeks (only on cold mornings) that when I start up my truck, it go to high idle, but after a little while of driving it comes down, and surges really bad between 600 and 100 RPM and sometimes it will die. It runs fine when it is given gas, and on the highway, it just does this at idle. Both in gear and out. Yesterday it did it in the driveway before I left and died, threw the MAF code. Changed the MAF sensor, and thought everything was good, but today it did the same thing on the way to work, surging in rpm but not dieing this time. No codes or check engine. In fact the only time I had a check engine was yesterday when it died.

 

Here is what I have done so far.

 

Cleaned out the throttle body, not perfectly, but removed as much as I could, and replaced the MAF Sensor.

 

Any suggestions on what to try next. Have a data logging program and code reader thing for my laptop. I am going to try to plug it in and see if there are any pending codes, and watch exactly what is going on tomorrow morning.

 

Thanks

[Norseman]

Check for an intake leak.