4.8 surge at idle

We have a 2000 Silverado 1500 with the 4.8. It has a surge at anything under 1200 rpm. If you snap the throttle it will hang at 18-1900 rpm and drop to 600, run like crap and stumble its way back up to 714 to 1010 in park. The surge isn't rhythmic. I had 2 codes, one I forced P0102 mass air signal low and the other was P0507 idle control system (RPM too high). I had a bad intake gasket that I replaced, cleaned the throttle body, cleaned the MAF and it still surges. I unplugged the MAF (I believe forcing the code) to put in speed density and it would idle about 1000-1100 rpm and relatively steady so that I could check for vacuum leaks. I borrowed a good MAF from my bosses 2000 5.3 Suburban and no change. I'm thinking that there is a problem with the IAC but I'm not sure. Below are the results from my scanner and they are are the 714-1010 rpm "idle" unless noted. Can you help me out?
TPS 0.59
O2 B1 S1 39
O2 B2 S1 30
02 B1 S2 26
O2 B2 S2 43
INJ PW 3.2 (Both banks)
ST TRIM -1 52
LT TRIM -1 25
ST TRIM -2 52
LT TRIM-2 25
TRIM AVG 0.0 (on all)
FT LEARN YES
FT CELL 17
MAF HZ 2067
MAF GM/SEC 3.14
MAP HG 11.3
MAP V 1.46
BARO HG 28.7
BARO V 4.59
COOLANT 203
IAC POS 0
DES IAC 0.00 (But I did see it flash as high as 1.19 still at idle)
VTD FUEL OFF- What is this?
IGN FUEL VTD NO - What is this?
SPARK ADV 14-16
KNOCK 0
EGR CLSD V .70
DES EGR 0
IGN V 13.8
DES IDLE 575

In the functional tests section I found 3 interesting tests.
IAC function, I could force idle up to 1200 but unless I snap the throttle I couldn't force the idle down below that 714-1010 rpm.
CYL miss index, according to the scanner anything below 1000 is good. At 714-1010 rpm it is 94. After snapping the throttle and getting it to idle down before it climbs back up it was 65526!
CYL MISS FIRE, nothing showing a particular cyl issue. but zero miss fires at that 714-1010 rpm but consistent miss fires between 18-20 per 200 revolutions at that snapped throttle 600 rpm idle.

Sorry for the long post but I just simply don't remember enough on scanner readings.

Did you try to check for an intake leak. I would try the good old carb cleaner trick. With the engine running spray around the manifold if the engine jumps up in idle or stalls you have an intake leak also check the egr. valve

Quote:

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Originally Posted by jaysonolson

Did you try to check for an intake leak. I would try the good old carb cleaner trick. With the engine running spray around the manifold if the engine jumps up in idle or stalls you have an intake leak also check the egr. valve

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I did.That was how I found the bad intake gasket. Afterwards I had to unplug the MAF to run smooth enough to verify that there wasn't a leakage issue.

http://i178.photobucket.com/albums/w...psqgnpfnne.jpg
Son of a... How did I miss THAT?

Wth happened? Looks like it was drilled or something...

good to see you found it. That's a weird place for a hole. Did you have any back fires?

I'm wondering how it happened as well. I don't know if maybe there was a vacuum line fitting there before or not. The truck was hit hard enough in the front end to push the cab into the bed.

isnt there a studd coming through the firewall right there that the heater core is bolted to? directly behind your mirror in this picture?

About 4-5 inches above the hole there is a stud that sticks through the firewall. That stud is bent to the passenger side. I know that this truck was totalled and that it was hit hard enough to push the cab into the bed but I'm truly amazed at how far that engine must have moved. I know that the frame is bent and one of the wheels was bent but I have a set of stock GMT400 aluminum wheels on it currently and it actually drives quite nice.