juyanith

I have a modified '07 Z06 that seems to have an issue with idling high. The car has a killer bee intake, torquer 110 cam, kooks headers, no cats and a corsa exhaust. I first take the car out it seems to idle just fine at around 900 RPM however after driving for a bit it likes to idle high, sometimes up to 1400 RPM.

The behavior is that when I'm approaching a stop, I let off the throttle and put the car in neutral, and it idles down to 900 RPM nicely while the car is moving. As I finally come to a complete stop the car will idle up to 1300+ RPM sometimes for a few seconds and then drop down. However, it seems that after driving around town for a while it will idle up and never settle down to 900. After doing this for a while I'll get a CEL (P0507 - Idle Air Control System RPM Higher Than Expected).

Now, here's the thing. The car has a locked PCM currently so I can't really get in there to check the idle settings, but it may also be a mechanical issue. I'm guessing that a vacuum leak might be part of the issue, but I'm kind of thown off by the idle jump when coming to a stop. Any thoughts on what I can check mechanically while I'm trying to get the PCM unlocked?

Bill Curlee

Have you had a ECU re-tune done. If not,,, I suspect that is the primary issue.

BC

juyanith

The car was modified when I bought it but I believe the only change after the tune was the intake. Once I get the PCM unlocked I'll look at the tables and see what's up. I did some checking last night and there are a couple of things that I found. First, the hose clamp that is on the throttle body is not very tight and I can actually turn the intake by hand. It's not going to come off but it's not snug either so I'm going to find another clamp and see if that helps. Second, the U-shaped PCV hose seems loose to me where it connects to the intake manifold. That is, the hose seems like it is stretched open and isn't really making a good seal. I thought about trying to put on a hose clamp but I don't think I could get to it to tighten it down. Is this a known issue or am I just imagining things? I could pull it off again and take a picture but basically it just seems like the inside diameter is a bit too big.

Bill Curlee

Any vacuum leak can cause idle issues. Yes, the PCV fitting is a known issue. They dry rot, get soft and fail frequently. Fix all the known air leaks and see if that makes any difference..

BC

eboggs_jkvl

Sounds like an air leak to me and probably after the MAF.

Elmer

Mez

The short U-shaped hose going from the valley to the intake manifold is stamped 11/32" . Mine was very tight. Is yours original? Its molded to that shape.

The hard plastic lines for the EVAP system do seem loose, but they usually seal up fine.

juyanith

I think the U-shaped hose is original (it is marked as 11/32) but it isn't very tight. The top part that goes into the intake is definitely flared and is a larger diameter than the other end. The whole thing comes off quite easily so I'll just replace it and see if it helps. For now, I've replaced it with about a foot of 3/8 hose.

I also replaced the hose clamp where the intake connects to the throttle body and it's got a nice seal now. I'll just have to see if the symptoms go away.

p.handle

Did you ever resolve this issue? I'm currently having the same problem. Car ran fine, then I changed the exhaust. I'm currently trying to tune it, but it does't seem to be a tuning issue. And I cant find a vacuum leak.
Thanks

ClothSeats

Z06 comes with dual-level vacuum-powered muffler sound modes (RPO code NPP). When your exhaust system was changed over, was the existing vacuum actuation addressed such that the vacuum source wasn't left open to the atmosphere?

p.handle

Hey that's a good thought. I didn't change the mufflers. Only the headers and x-pipe. But they were knocked around a little bit aligning the new pipes. I will check all that if I get a chance this week.

Thanks for the input.

~p