What internally could causes surge at idle
What internally could causes surge at idle I've got a 2000 WS6 LS1. I built the engine (228/228 cam, 241 heads, FAST 90 intake, Nick Williams TB) nothing special, and this car was a daily driver for about 60000 miles. I had it tuned when I built it, but it always had a surge. The tuner could not figure it out and gave up. I drove it with the issue b/c I figured out how to peddle it and basically just got used to it. I parked it for a while and have recently started messing with it again. I changed the heads and injectors on it and took it to another tuner. We started thinking the intake was leaking and he smoked tested it, but didn't see any issues. To be sure, I went ahead and swapped it out with an LS6 intake but it's still surging. I also changed the IAC in the process. I have no idea where to go from here. I have figured out that if I unplug the IAC, the surge goes away and it runs perfect. I have reworked all of the lines that could cause a vacuum issue, but still no luck. My tuner says that everything he is seeing looks good on his end. I trust him, b/c he has some cars at the shop with basically the same set up as me and they are running perfect. He has put in some time on this car too with no charge, b/c he just wants to know what it could be too. I've basically swapped everything on the top side from heads to the TB but still have the same issue. It seems to get a little better when it warms up, but at cold start it's a lot of surging and you can hear a LOT of air getting pulled in through the hood. Is there something internally or electrical that could be causing this is what I'm starting to wonder?
Last edited by smokdya; Nov 17, 2022 at 02:45 PM.
FWIW - I think testing the alternator & battery to a least rule them out might be worthwhile.
My 416 started to feel like it had surge. Shortly after that I noticed at night the dash lights & head lights flickered or surged. The surge gradually got worse.
My car's issue was the alternator was failing. The voltage regulator was bad. New alternator fixed the issue. I also had to replace the battery shortly before the alternator issue. I'm guessing the bad alternator helped kill my 2 year old battery. Not saying that is your car's issue.
Wish you the best with troubleshooting your ride. Sounds like a sweet set with cam & intake etc!
My 416 started to feel like it had surge. Shortly after that I noticed at night the dash lights & head lights flickered or surged. The surge gradually got worse.
My car's issue was the alternator was failing. The voltage regulator was bad. New alternator fixed the issue. I also had to replace the battery shortly before the alternator issue. I'm guessing the bad alternator helped kill my 2 year old battery. Not saying that is your car's issue.
Wish you the best with troubleshooting your ride. Sounds like a sweet set with cam & intake etc!
FWIW - I think testing the alternator & battery to a least rule them out might be worthwhile.
My 416 started to feel like it had surge. Shortly after that I noticed at night the dash lights & head lights flickered or surged. The surge gradually got worse.
My car's issue was the alternator was failing. The voltage regulator was bad. New alternator fixed the issue. I also had to replace the battery shortly before the alternator issue. I'm guessing the bad alternator helped kill my 2 year old battery. Not saying that is your car's issue.
Wish you the best with troubleshooting your ride. Sounds like a sweet set with cam & intake etc!
My 416 started to feel like it had surge. Shortly after that I noticed at night the dash lights & head lights flickered or surged. The surge gradually got worse.
My car's issue was the alternator was failing. The voltage regulator was bad. New alternator fixed the issue. I also had to replace the battery shortly before the alternator issue. I'm guessing the bad alternator helped kill my 2 year old battery. Not saying that is your car's issue.
Wish you the best with troubleshooting your ride. Sounds like a sweet set with cam & intake etc!
It was at 4.6. I twisted the idle screw till it pulled it up to 5. Not sure if this is the correct way to adjust, so let me know. It surges with real quick surges. I can bump the throttle and it will idle around 1100 and slowly come back down and start surging again. 1 out of 10 times, I can get it to idle low and run perfect, but when I turn it off and back on, it starts all over. I just included a video of what it's doing in my original post.
Last edited by smokdya; Nov 17, 2022 at 02:47 PM.
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It was at 4.6. I twisted the idle screw till it pulled it up to 5. Not sure if this is the correct way to adjust, so let me know. It surges with real quick surges. I can bump the throttle and it will idle around 1100 and slowly come back down and start surging again. 1 out of 10 times, I can get it to idle low and run perfect, but when I turn it off and back on, it starts all over. I just included a video of what it's doing in my original post.
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Verdad Gallardo Last edited by smokdya; Nov 17, 2022 at 07:03 PM.
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No offense intended but he can't be that great if he can't figure this out. Doesn't matter what's wrong with it. Just because he's tuned a ton of set ups just like yours, thats really not a skill set. Finding out why one in a million didn't turn out the same might be.
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If unplugging the IAC works, then the IAC command is likely driving the issue. RPM overshoot/undershoot from target idle speed. Like a damping factor needs to be adjusted.
Also, how is your PCV routed? There needs to be a restriction in it, fixed orifice. PCV air also needs to be accounted for (measured) if you are running a mass air meter.
Also, how is your PCV routed? There needs to be a restriction in it, fixed orifice. PCV air also needs to be accounted for (measured) if you are running a mass air meter.
If unplugging the IAC works, then the IAC command is likely driving the issue. RPM overshoot/undershoot from target idle speed. Like a damping factor needs to be adjusted.
Also, how is your PCV routed? There needs to be a restriction in it, fixed orifice. PCV air also needs to be accounted for (measured) if you are running a mass air meter.
Also, how is your PCV routed? There needs to be a restriction in it, fixed orifice. PCV air also needs to be accounted for (measured) if you are running a mass air meter.
I will get with my tuner about adjusting the damping factor and see if that’s something he’s looked at. I’m not running a mass air meter. Thanks for the help.
Has fuel pressure been checked to see what it is and to see that it doesn't fluctuate? A weak or failing fuel pump might cause surge. Likewise a fuel filter that needs replaced. Another possibility to check.
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Joined: Oct 2022
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From: FL
OP did mention the problem was there after first tuner, who gave up so it was driven with the surge for 60k miles. Now it was looked at by another tuner. I would think someone would have figured that out by now, but who knows.
Surging at idle with higher overlap cam is often because the ECM is making changes too quick resulting in the engine hunting for target idle. Basically it is constantly overshooting and undershooting target and that causes the hunting. It also can be caused by incorrect fueling or base spark timing in the tune, so that the ECM is having to compensate too much to control idle.
I'm not familiar with GM ECM idle settings, but my Holley ECM allows me to adjust the PID settings for idle spark control and IAC. Lumpy cams bounce by nature and you gotta slow down ECM decision making by adjusting PID settings, and range of allowable RPM swing to remain in idle control mode. There's got to be something similar in the GM ECM to get the ECM to chill out a bit and stop trying to make idle adjustments so fast.
As always, tuning idle is never really possible without first setting the base airflow correctly with throttle stop screw. Then the real tuning can begin. Tuning idle is actually one of the most difficult tasks a tuner encounters. If your tuner can't figure it out then don't even hesitate to try somebody else until you find somebody that can.
I'm not familiar with GM ECM idle settings, but my Holley ECM allows me to adjust the PID settings for idle spark control and IAC. Lumpy cams bounce by nature and you gotta slow down ECM decision making by adjusting PID settings, and range of allowable RPM swing to remain in idle control mode. There's got to be something similar in the GM ECM to get the ECM to chill out a bit and stop trying to make idle adjustments so fast.
As always, tuning idle is never really possible without first setting the base airflow correctly with throttle stop screw. Then the real tuning can begin. Tuning idle is actually one of the most difficult tasks a tuner encounters. If your tuner can't figure it out then don't even hesitate to try somebody else until you find somebody that can.
Last edited by QwkTrip; Nov 18, 2022 at 03:24 PM.
pump and filter about 3 months ago. Thanks though.