96 GMC Sierra 5.0 to 5.7 idle surge

[mphmilkman]

I have replaced my tired 1996 GMC 5.0 with a fresh 5.7. The idle was slightly unstable after the work was finished. I installed a Crane cams energy extream cam that was ment for this model year and souldn't cause drivability problems. I had the VCM reflashed with calibrations from an identical truck with the 5.7. Now the truck has better shifting and more power. The only thing that went down hill was the idle. Now it idles fine in park but when it warms up and is put in gear it will go down to 500 and loap from 500 to 1000. If you put on the AC it won't do it because of the IAC stepping the idle. I researched all the engine related parts and found no difference in any part number. Did I miss on of the parts that was different?

[mphmilkman]

I have found that the truck I got the vin from had 2 cats. The VCM is seeing the emissions from all 8 cillinders instead of one bank. I beleave this may be the problem. I ordered an o2 simulator for testing behind the cat.

[mphmilkman]

ok more info. the o2 and exhaust problem is not causing the lope. The cam I anstalled was a COM CAMS energy extreme 4X4 hydrolic roller. not a Crane. The specs are duration 264, 269 lift 488, 495. This cam is listed for 1996. The idle was 700 with the 305 and with the reprogramming for the 350 it drops to 550. Has anyone installed this cam with the same problems?

[mphmilkman]

Comp cams said the cam is for a vortec with a modified computer. I need a slightly higher idle setting. Looks like only 100 rpm. Anyone know of a way asside from opening the throttle blade. I opened as far as it would go and the IAC still compensated for it. I thought about trying to space the Iac out away from the housing slightly so that it would let a small amout of air pass by even at 0 counts. Anyone have any other ideas? Asside from 400 dollars for a custom calibration VCM.

[fuzzypuppy]

different cam same problem, I purchased the largest cam Edelbrock said would work with my stock computer, it does work but it does lope at idle and being computer controled the computer tries to compensate for the lope with an irratic "searching" idle, just a little quirk I have learned to live with over the past 18 months it's been installed, at first I thought it was a problem sensor etc, but it only started after the cam install, and it idles where it is supposed to, just kind of funky,

[mphmilkman]

Sounds like I should have gotten the cam you did. My idle is sometimes jumpy enough to move the truck with the brakes on. What I do is give it a little bit of gas when it happens and it will stabilize.