Is the install complete? Is the MAF sensor and filter installed? Is the PCV line that goes in the intake tube in correct location. These all can effect it as well as a simple vaccum leak from a ports on the intake not plugged.

 

Yes, installation is complete, along with MAF sensor and air filter, and he installed the MAF sensor at the midpoint of a long straight tube between filter and intake. He and I discussed the possibility of an air leak, but wouldn't the leak have to be between the MAF and the plenum to raise the idle speed? I'll suggest he check again for air leaks...

What's important about the PCV line?

 

The PCV is a vent for the crank the "fresh" air inlet is on pass valve cover (little metal tube) goes aft of MAF in the intake tube itself so its getting metered air. If its open then that is a huge vacuum leak. The outlet is on valley cover under intake and goes to intake behind TB usually a black accordion looking tube.

Also any leak on the intake itself is unmetered air and ECM doesnt know so idle will raise.

What is the code number its throwing?

 

To add a little to what BO185 is saying, the inlet for the pcv on an LS3 crate engine is a hard tube just above the passenger valve cover at the front of the engine.

 

Thanks again! I'd forgotten that the PCV fed into the incoming air line and thus would itself be 'unmetered' air into the engine (even without any leaks), but that's probably accounted for in the GM setup.

I didn't record the code itself, but the person checking the code told us 'high idle speed' was the only issue. He was using a Snap On version of a Tech II . Our simple checkers would not work at all with that engine/ECU...

 

Thanks again! I'd forgotten that the PCV fed into the incoming air line and thus would itself be 'unmetered' air into the engine (even without any leaks), but that's probably accounted for in the GM setup.

As I mentioned if its connected to intake tube aft of MAF its metered air and accounted for in tune. The locations I noted in post #4. If not its unmetered air and could cause the high idle as the ECM is trying to get it to idle right.

Also the idle will learn so over time were it once to be the base tune has on idle set typically 600-700 rpm on stock motor. Now usually higher on the 525 due to cam i would have to look up the stock GMPP tune but thought it was around 800rpm base idle and high idle was 900ish then go down to base. So check for leaks and the correct PCV setup then drive it for a while let it learn. IF still high have a tuner check the idle setting if its never been tuned then its the correct settings.

Also if your unhooking the battery you lose idle learn and fuel trims everytime.

 

BO185,

If the PCV connects AFTER the MAF, would the PCV then be supplying unmetered air to the engine? The MAF meters the incoming air if I understand it correctly...

 

After meaning down stream IE aft of MAF air moves through MAF and metered then into PCV tube and then TB.

So install is air filter, MAF, PCV tube, TB. Air moves through air filter then MAF gets metered, them moves a small amount through PCV tube, rest goes to TB. All air after MAF is metered so ECM knows the amount of air so it acount's for PCV air, meaning it knows total air in motor. So it can adjust TB idle as needed.

 

To find what the commanded idle is, you have to be able to view the program, using a tune tool, such as EFI LIVE, HP Tuner, etc.
There are several maps that are involved, such as cold start, decay, etc.
Those tune tools are also capable of data logging. Absolutely a must, to really get the tune correct.

 

Followup: Owner has had it checked/tuned and was told that a 900 rpm idle (and an MIL due to high idle speed) is not unusual for this engine/ECU. The car drives/runs great and the higher idle doesn't cause any apparent problems, so the owner is not concerned any longer.

 

The six speeds and that cam like the higher idle, but tend to surge just driving around a parking lot in 1st. I bet its the GMPP controller they are set a like 850 but the ECM actually learns idle so it goes higher hence the code. One thing to note make sure he isn't disconnecting battery power to ECM with a kill switch or batt disconnect when he parks the car.