5.7 Vortec Surging

Anyone had trouble with a surging problem? This happens only after the motor is fully warmed up, in drive or reverse, and with the brakes on. Will get about a 200 rpm swing on the tach, surge a little, idle ok, then surge again repeating this. Let off the brake and start to roll and the idle straightens out normal. Any ideas?

It could be early sign of brake booster going bad. It has a diaphram in it and has vacuum from the intake manifold. You may hear a slight hissing sound from under the dash or the brakes may be a little harder to apply. :2cents:

Same problem i am having. did you find anything?

Milkman, you may try removing your master cylinder from the booster and checking the condition of that little rubber gasket. I just encountered that surging problem, killed my gas mileage, but the reason turned out to be a ripped gasket. The grease that lubricates the gasket to the plunger that moves forward through it was all gone. I could hear something leaking inside the truck with everything off and the windows rolled up. If I pressed on the brake pedal lightly, the hissing would go away, and then it would come back. All the while causing engine surging, sometimes the truck died if I hit the pedal hard enough. Good Luck -Chris

Before you pull the brake booster off (which means the master cylinder as well), just pull off the vacuum line and plug it. If the problem goes away, the problem is the diaphragm. Don't drive it like this however, you will have no power assist in braking.

Well I wish it was as simple as the booster. I tryed a vacuum canister to help with vacuum with no success. It turns out Summit sold me the wrong cam. It is ment for a vortec with a modified computer. I need a slightly higher idle setting. Possible only 100 rpm. I have tryed opening the throttle blade and the VCM still compensates for it. Now I am trying to space the IAC out slightly so that when It is at 0 counts it will be slightle open. Probable won't help but I thought I would try.

I know this is an old post, but I finally found the cure.......knock on wood. It would do this surge like clock work every day. It's been 2 1/2 weeks now and hasn't even tried to surge.

1st of all........my hat's off to tempfixit for posting that free online service manuals. Did some digging and found some service bulletins on this problem. One update mentioned a transmission calibration. Brought it in to a buddy of my brother's at the Chevy shop in town. He removed the software from the computer, went inside and downloaded all the updates off of the GM web link, downloaded this back onto my truck's computer and that was all she wrote...CURED. This took maybe 15 minute to do this!!!!!! No surge, great idle. Went back home and reinstalled my Hypertech 3 back on. Just wanted to share this......saw that this has been a problem for some people. THANK YOU tempfixit.