Chasing possible Vacuum Leak ? LTFT's +20 at Idle

[Indyblue98]

Long Term Fuel Trims are reading +20 to +25 at idle (SCT TUNER )
Both Bank 1 and Bank 2 , But only at low rpm under 900

Driveabilty is good , and the LTFT's look good while driving.

Jannetty is providing tuning and wanted to see if there is a Vacuum leak .
Checked the easy stuff like Throttle Body and Catch Can.

Tried putting smoke around the edges of the intake .

Nothing obvious yet.

If there is a bad seal on one of the intake ports would that make both banks reading bad ?

Any ideas ?

[Nessal]

I had this EXACT problem. Car drove fine but it read that LTFT were at 20%. Turned out that the intake manifold seals were leaking on cylinder #8 causing the car to run lean. The dealer replaced the complete manifold and since then everything has been good. My LTFT have been +-2% verified by my OBD scanner.

The dealer showed me the old plastic manifold and sure enough, the number 8 runner was melted and the gasket was all distorted. They said that it was most likely an assembly problem at the factory.

[greenmachinedriver]

You can try spraying carb cleaner around any posible source and.watch your scanner to see if the short term fuel trim changes. You should see a momentary drop in stft if there is a leak.

[BlackM6RS/SS]

Do you have a fast intake?

[GearBangr]

Originally Posted by Nessal

I had this EXACT problem. Car drove fine but it read that LTFT were at 20%. Turned out that the intake manifold seals were leaking on cylinder #8 causing the car to run lean. The dealer replaced the complete manifold and since then everything has been good. My LTFT have been +-2% verified by my OBD scanner.

The dealer showed me the old plastic manifold and sure enough, the number 8 runner was melted and the gasket was all distorted. They said that it was most likely an assembly problem at the factory.

Its weird you mention that. I work at a full service shop, and last year I had a similar issue with a pickup. It was a 2010 with around 10k miles. The ses light was on, it was setting lean codes, and the ltft were in the 20s. I used our smoke machine and sure enough there was smoke coming from #8. When I pulled off the intake, 8 had the runner melted, enough to where light was visible. So maybe there was a bad batch of intakes that got out. I think I have pictures of it actually.

[Nessal]

Originally Posted by GearBangr

Its weird you mention that. I work at a full service shop, and last year I had a similar issue with a pickup. It was a 2010 with around 10k miles. The ses light was on, it was setting lean codes, and the ltft were in the 20s. I used our smoke machine and sure enough there was smoke coming from #8. When I pulled off the intake, 8 had the runner melted, enough to where light was visible. So maybe there was a bad batch of intakes that got out. I think I have pictures of it actually.

They had their heads scratching for a day or two before smoking the manifold to isolate the problem.

[GearBangr]

Originally Posted by Nessal

They had their heads scratching for a day or two before smoking the manifold to isolate the problem.

Lol, that's usually my next step if I can't find anything visually or by sound.

[bad55nomad]

I had the same problem ending up being ported throttle body . Took it off problem solved

[Aries240SS]

A bad TB gasket seal can do it, or if the manifold was cracked when the TB was installed and now has a leak. You'll need to smoke the manifold to find the leak if you've already checked the hoses. Sometimes just smoking the edges won't reveal the problem.

[1LEsteiny]

I might have to look into 3d printing each end and use regular brake ducts between