idle surge issue
TECH Enthusiast
Joined: Sep 2005
Posts: 503
Likes: 54
From: TX
This should never be necessary on a stock internal/stock TC LS1. They didn't surge from the factory, so when this happens on a minor bolt-on car it's because something has gone wrong.
Opening the TB blade further would only be a cover up, reducing the effectiveness of the IAC (and thus PCM controlled idle conditions), and would likely introduce other issues on a stock engine (such as idle hang and cruise control effect).
Opening the TB blade further would only be a cover up, reducing the effectiveness of the IAC (and thus PCM controlled idle conditions), and would likely introduce other issues on a stock engine (such as idle hang and cruise control effect).
With no after effects.
Joined: Nov 2001
Posts: 34,659
Likes: 2,581
From: Schiller Park, ILL Member: #317
For a stock engine, that set screw should only be holding the TB blade open far enough to prevent it from sticking in the bore when closed.
As for side effects, they definitely exist, especially for the A4 cars. Many years ago, before custom tuning was easily available, many of us would crack open the TB blade or enlarge the air bleed hole in the blade to get our cammed LS1s to idle. This always led to some degree of idle hang or cruise control effect under certain conditions. There was usually a sweet spot between excessive surge and excesssive idle hang, but even the sweet spot was still not a perfect fix under all conditions. M6 cars were more forgiving though.
TECH Enthusiast
Joined: Sep 2005
Posts: 503
Likes: 54
From: TX
It's not really a "fix", just a cover up. They didn't come off the assembly line having this issue, so if the car is still stock then something has gone wrong somewhere to cause this problem.
For a stock engine, that set screw should only be holding the TB blade open far enough to prevent it from sticking in the bore when closed.
As for side effects, they definitely exist, especially for the A4 cars. Many years ago, before custom tuning was easily available, many of us would crack open the TB blade or enlarge the air bleed hole in the blade to get our cammed LS1s to idle. This always led to some degree of idle hang or cruise control effect under certain conditions. There was usually a sweet spot between excessive surge and excesssive idle hang, but even the sweet spot was still not a perfect fix under all conditions. M6 cars were more forgiving though.
For a stock engine, that set screw should only be holding the TB blade open far enough to prevent it from sticking in the bore when closed.
As for side effects, they definitely exist, especially for the A4 cars. Many years ago, before custom tuning was easily available, many of us would crack open the TB blade or enlarge the air bleed hole in the blade to get our cammed LS1s to idle. This always led to some degree of idle hang or cruise control effect under certain conditions. There was usually a sweet spot between excessive surge and excesssive idle hang, but even the sweet spot was still not a perfect fix under all conditions. M6 cars were more forgiving though.
Meh, never had those issues.
OP does your car do this at all? Or anyone else?
https://ls1tech.com/forums/pcm-diagn...-like-you.html
https://ls1tech.com/forums/pcm-diagn...-like-you.html
Many years later I would say to check the valve cover gaskets and make sure the valve covers are torqued down. Replace the PCV valve complete hose setup. It is 85% fixed I am going to replace the IAC with a new DEPHI unit and report back.
You know what mine was when it was doing this??? A crack in the exhaust manifold on the driver side. Between the manifold and the cat. Just enough of a leak that not a single shop in town could figure it out. I fought with it forever.... even told a few places that I was thinking a small leak.. Well, the weld on the flange where it connects to the cat finally gave up all the way while driving home about a month ago. I took it apart rewelded the flange on, reinstalled and bingo no more surging. Problem solved
