udienow

iTrader: (18)

So I installed a LS6 intake for my friend last week and since then it has had this strange issue. Worse yet its not 100% every time sometimes it works fine. The problem we are having is when you start the car it idles fine, 650 rpm in drive. Once you let off the brake and the car starts rolling forward after a few secs the cars RPMs will shoot up on their own to like 900-1000 or so and the car will basically accelerate itself more so than usual. When driving at like 30 or 40mph it feels like you have cruise control on as the car almost maintains speed without being on the gas. If you pop it in neutral while driving it will sit at around 1400 RPM. When you come to a stop again it will after 1-2 secs idle as normal at 650, but again once you let off the brake and start rolling it will kick up the RPMs a little bit on its own.

Here is everything that I have already tried to no avail:
Swapped working IAC from my TB to this car, no change
Swapped working TPS from my TB to this car, no change
Checked dozens of times for vacuum leaks, not finding a thing
Did the IAC and TPS reset where you unplug it for 30 secs, no change
Reset ECU by unplugging battery, no change

There is no check engine light and everything is connected as it should be. I am just out of things to try other than to take this whole thing off again, but I just know I wont find anything wrong under there either. Could this be something with the tune? Again though only thing that changed was the ls6 intake, I didn't touch anything else, and everything ran perfectly fine before.
Any ideas?

garygnu

how did you check for vacuum leaks.check the intake runner gaskets.check the PCV system for leaks.

raysadude

iTrader: (11)

Try to use brake cleaners, spray it all over the intake and at the back of the intake manifold, if your rpm change you got a vacuum leak in that spot

Darkman

iTrader: (2)

When I had an LS6 intake it would leak unless I followed the two step torque porcedure (44 inch pounds, then 89 inch pounds) in the sequence in the Service Manual. The symptoms when it leaked are the same as yours.

Old Geezer

iTrader: (3)

Data log it, and look for weird input[s]....

BrntWS6

iTrader: (7)

If your sure there are no vacuum leaks it's in the tune.

402GOAT

iTrader: (2)

Isnt there something on the bottom of the intake that you have to trim in order for it to fit??? This could be an issue if the intake is not seating down completely.

BrntWS6

iTrader: (7)

^If you mean rounded valley cover bolts that's only needed for FAST intakes.

402GOAT

iTrader: (2)

I was thinking it was something with the crossover coolant pipe. I may be wrong though.

SSmoked1

iTrader: (21)

If its a 98-00 then it needs the rear block off's and front steam tube. Or you can keep the stock steam tube and chisel off the fins on the bottom. That's what I did before I got a fast.

Did you torque in sequence like Darkman posted?

bayer-z28

iTrader: (14)

^ Don't chisel the ribs off. People have broken their intakes that way.. Just use a dremel and cut them off.. Much safer.

And we're finding that the rear coolant block offs aren't really the greatest idea. Still working on an idea to connect all 4 again. Back cylinders get too hot.

udienow

iTrader: (18)

The intake he bought already had the ribs sanded off. So we left the old coolant lines and the intake went on without a problem.

As far as torquing down the bolts, I did follow the sequence that was posted above, but the problem I had was my torque wrench would not fit the back 4 bolts, so I had to guess on those.

There must be a vacuum leak somewhere... I will go through it with brake cleaner... I must be missing something...

needtransam

iTrader: (2)

try a fog machine, that will tell you if you have a leak pretty fast

RevGTO

iTrader: (12)

Did you disconnect the battery when you did the swap? That could have started it. If you don't have a vacuum leak, those are the exact symptoms of an idle relearn. I've found that it just takes time for it to reset, no matter how many of the procedures that I've tried to get it done. Now that you disconnected it after the fact, you can expect it to take a while.

BTW, I have a similar thread in the PCM forum as my car started to do this out of the blue and I've tried a lot of similar things as you but so far no fix.

udienow

iTrader: (18)

Sprayed TB cleaner all over all hoses to search for vac leak (again) 0 idle change no matter where I sprayed. It was hard to get it in the back but nothing changed when I did spray back there as best I could.

Got a smaller inch lb tq wrench and took out all the bolts, reseated the intake, and tightened all bolts in sequence to spec (44 then 89 inch lbs) again... still have the issue after.

Battery was disconnected during install as well as again after...



I am fairly sure this is not a vacuum leak or anything to do with anything I did incorrectly. I am now fairly convinced that its something with the tune or I guess it's re-learning? My only problem is why is this intermittent? Sometimes the car drives 100% correctly the whole time its on... then if you turn it off and on again it does it even though it was just fine 1 min ago. So like re-starting the car sometimes makes it work correctly most other times not. It's so small too, only kicks it up like 200 rpm, but still does it. If it is something with the tune... does it make sense that it only does it sometimes?

SWEET98SS

iTrader: (8)

Did you connect the small vacuum hose that goes from the passenger side air a/c box to the back of the intake? One way to see if this is off is put your vent on hi and put it to come out in the middle vents, if it doesnt, this hose is off.

Just had this happen to me. My car was idling really high, push the clutch in while driving, it would idle at 2000.

RevGTO

iTrader: (12)

This is exactly how my car behaves after reflashing the PCM and it usually takes about six weeks of daily driving for it to relearn and completely disappear. The same thing happens when you disconnect the battery. So I really doubt you have a vacuum leak or any other problem.

But in my current case, it the exact same behavior started out of the blue about four weeks ago for no apparent reason. It is intermittent but gradually becoming less prevalent - from about 85% of the time to about 60% now.

udienow

iTrader: (18)

This hose is connected, vents work fine on all settings.


Really 6 weeks? Wow.. i guess there is no harm in waiting to see if it goes away on its own.

RevGTO

iTrader: (12)

Other people on other boards have also expressed amazement that it takes that long, but that's how it works for me. All the reset procedures I've tried haven't shortened it either. Then again, most of my driving is short trips in town. If you drive a lot on freeways it might take considerably less time.

raysadude

iTrader: (11)

If you tune the car yourself plug in to the laptop and make sure your MAP sensor is working. When mine was broken it did the exact same thing. ie:while driving if I press the clutch it'd idle around 2k or so