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Did a simple LS1 to LS6 intake swap today. Ditched all the erg provisions. Hooked everything back up and now the car doesn’t idle right. Starts fine then slowly reduces to around 400 rpms and barely stays running. After a few hits on the throttle the idle come up but is not consistent. Goes from 900 to 700 back and forth. I let it run awhile thinking the pcm needed to relearn some files but no change. Driving down the road it runs fine. Just doesn’t want to idle consistently. Anyone had this problem with a intake swap? My next move is to pull the intake back off to check for leaks?
Sounds vacuum related to me. The one on the back of the intake is notorious for coming off.
I just did the same swap and for an unrelated reason I changed the 3 way vacuum check valve. My car idles better now. I thought that was odd but for the low cost is something to consider changing if you don’t make any progress.
Sounds vacuum related to me. The one on the back of the intake is notorious for coming off.
I just did the same swap and for an unrelated reason I changed the 3 way vacuum check valve. My car idles better now. I thought that was odd but for the low cost is something to consider changing if you don’t make any progress.
Are u talking about the T that the line from the intake plugs into? Pics.... I'm intrigued
definitely vacuum leak. Either intake wasn't torque, gasket is bad, or 1 of the vacuum lines on the back of the manifold or side is loose/missing/cracked.
Here is a crappy pic buts all I have. This is near the firewall on the passenger side. It’s the white thing just below my index finger. The part is white and black but I think you’ll easily find it when you look there. Twist then pull the vacuum tubes off. Gently!
Ok. Pulled the intake back off and double checked to make sure I didn’t have a gasket fold or something. Every looked good. Re-installed and torqued to spec. Same problem. Next question is: how do I check for bad vacuum lines? Or do I just replace for good measure? Getting tired of scratching up my hands and arms taking this damn intake on and off 😡
There are multiple ports on the intake at the front. Front driverside is EVAP. The TB also has a port or 2. They need to be plugged or connected to the hose that was there. Rear of the intake has 2 ports, 1 to the brake booster and 1 to a vacuum reservoir. Spray brake cleaner around the intake with the car running and see if the rev's change. It'll tell you where the leak is.
before you cause yourself a lot more work for no reason you need to log it and check for DTC's
log RPM, IAC counts, STIT, STFT/ LTFT front 02 voltage and TPS %.
Is this car stock? Have you ever adjusted the idle set screw?
spraying carb cleaner doesn't do much on a EFI to find a leak, not like on a carb.
to find a vacuum leak, monitor STFT and front 02 voltage. when you spray over a leak, your 02 voltage will shoot up, your STFT will go negative.
Another good way to check for leaks is drill a 1/8 hole in the top of a water bottle and spray water down the side of the intake. if you do have a leak, it will suck the water in. you will see and hear it and no you aren't going to hydro lock your engine.
Last edited by LilJayV10; Jun 28, 2019 at 09:50 AM.
Ok. Pulled the intake back off and double checked to make sure I didn’t have a gasket fold or something. Every looked good. Re-installed and torqued to spec. Same problem. Next question is: how do I check for bad vacuum lines? Or do I just replace for good measure? Getting tired of scratching up my hands and arms taking this damn intake on and off ��
Get a pair of side cutters and cut the tips off the cowl plastic push pins.
there are only so many vacuum leak points associated with a mani removal.......intake gaskets....rear vacuum ports, power brake, HVAC and AIR solenoid .....and rear PCV hose....gotta be 1 of those
many other vacuum leak points but not mani related
Took it back off so I could inspect the PCV and vacuum lines better. Found a slight kink in one of my PCV lines is all I found. Everything else seems good. Would the PCV hose cause it to idle different? It’s my understanding that the PCV system is just for oil blow by off the heads correct?
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Erratic idle after LS6 intake install 
