Long term fuel trim too high at idle

wirelessf · #1 (**permalink**) 02-15-2008, 01:43 AM

For those who have a scanguage, there is a xgauge code that allows you to read the fuel trims. Pretty neat feature I should say, but then discovered a potential problem.

Is it normal for the long term fuel trim to be high at idle? The scanguage reads 22% at idle, but goes to single digits when I drive it. Is there a potential vacuum leak? Or is it normal for it to lean out at idle?

HOGWILD · #2 (**permalink**) 02-15-2008, 09:53 AM

Cold Engine RPM Idle? If so i think the ECM has control of this until engine warms to normal operating temp. If you are allready at normal engine temp and normal RPM's i think it would be an issue if reading was that high after a few seconds at idle RPM's!

wirelessf · #3 (**permalink**) 02-15-2008, 11:14 AM

yeah it was already at operating temp.

Tones · #4 (**permalink**) 02-16-2008, 10:03 AM

Don't know much about these parameters, but I read just the other day that when a MAF starts to go or gets dirty, it can cause a rich condition at idle and lean condition at higher rpms. One symptom is a slight loss of power. It may or may not set a code.

wirelessf · #5 (**permalink**) 02-16-2008, 05:05 PM

I looked around for some answers and the reason for this is that it could be an air leak.
How do I test for air leaks?

wirelessf · #6 (**permalink**) 02-17-2008, 06:23 PM

Well I checked the PCV valve, changed the grommet and changed the tubing going to the TB. Now it reads 13-17% LTFT (long term fuel trim) I zip-tied all vacuum hoses going to the intake manifold and replaced all stiff/cracked hoses.

Is it possible that an exhaust manifold leak could be the problem?