So I guess that "if it ain't broke don't fix it" thing must be true. Here's the dilemma:

I got my ls1 stocker intake removed and an ls6 intake I bought here on the tech forums installed, or so I thought. All the sensors I think I hooked up correctly, and I was pretty sure I got all the vaccum lines. So I go to start my car and it doesn't want to keep going. If you give it gas it keeps it turning over a few more times, but inevitably it dies.

Now the odd thing. So I'm going through experimenting with stuff because I did not want to rip the intake off again...I unplugged the MAF and go to start it and it works. It starts almost normally although a little rough sounding, but then it kicks idle up to about 2500rpm and finds a home in that range, idling way too high.

Is this maybe a vacuum problem that I'm dealing with? It would make sense that if the intake manifold was under higher pressure in SD mode, the PCM would treat it like it was under throttle and throw in some extra fuel, and the thing would rev as if you were opening the TB. Also I can't get autotap to throw any codes except for the MAF sensor when it's unplugged. I have no idea what's going on here. I want to avoid taking the whole assembly off again if at all possible, but it might come down to that. Does anybody have an idea on what might be wrong with this thing before I invest a bunch of time ripping the thing off? Thanks for any responses....

 

Yeah it sounds like a vacuum leak to me. When you did the swap did you make sure to hook up all the lines on the back of the new manifold. I'm not sure what sensor it is but you have to swap it from the old manifold to the new or there will be a hole in the back. Also, the brake booster line, did you hook it up to the manifold and the brake booster. Just some ideas.

 

yeah checked all those out to the best of my knowledge. I connected both the large and small vaccum lines on the back of the new manifold. The sensor that goes back there was swapped, and the terminal is connected. I can verify all that by feeling in the back of the manifold area. The other end of the large line is connected to the brake booster as it should be. The small end I assume is still connected to the HVAC on the other end........

So now it idles fine as long as its in SD. Although the STFT's read 99.8% or something like that in atap. Not sure if that's where they're supposed to be or what. As soon as I try to plug in the MAF for just a second the car tries to die. Wondering if the MAF might be the culprit, to be honest i did touch some wires because a couple blades had fallen in the lid/maf assembly when i was working on it. I'll do some research on here and find out what to clean it with and post my results. Thanks for the reply.

 

Did you remove the 2 plastic clips from the knock sensor wiring harness? They are taped on and need to be removed so the LS6 intake will sit flush with the heads.

 

also just for grins make sure you re-torque the intake. I found out through Atap that I as getting a rough idle and misfires and it turns out I missed a bolt or didn't get it tight enough. Problem solved for me.

 

yes, another good suggestion. I did take both of the clips off before I set the intake on...I've got it idling where it should now, but it only works in SD mode, now I'm leaning more towards the MAF being the culprit, if I messed it up somewhere during the install. The manifold pressure reads about 8.8mmHg at idle. If that's too far off, somebody tell me. I'm going to clean the MAF tomorrow and see if it works when I plug it in. If that's the case I'll just write this whole heavy idle thing off as something freakish. The vaccum lines all seem fine, it brakes as it should, and the HVAC controls all switch as they should since they're vaccum assisted. Hopefully this'll fix the problem.

I'll go ahead and give the bolts another pass and see if that helps as well.

 

PROBLEM FIXED (cleaned MAF sensor):

The 2500rpm idle thing is still completely inexplicable unless it took the PCM that long to find an idle in the SD mode. The 2500rpm's steadily came down over the course of running it for 30 minutes last night and it idled in SD afterwards. I drove around all day in SD and it seemed to run fine, then when I came home I unplugged the MAF, took off the ends, and proceeded to clean it with rubbing alcohol and q-tips. A lot of gunk came off, for which I cannot explain the origin unless it is from the Fram Airhog filter (K&N clone)...probably is actually, and it would have been the oil that came from the filter out of the box, as in I did not add any oil myself. I should have listened to everyone on the forums about staying away from these, but I did not. Odd thing is the MAF always worked great up until I swapped out the intake, and then it crashed all the sudden.

But this seemed to fix the problem. There is no longer a problem with idle, and the MAF works just fine when plugged in. And there seems to be no vaccum leak; manifold pressure is fine. I posted this up so maybe someone with a similar problem can see what one possible cause is. Thanks to all who replied.