2009 Buick LaCrosse CX 3.8 L26 V6 with engine code P0401 and P0106

Question

Got a quick question about these codes. 2009 Buick Lacrosse CX 3.8 V6

A couple weeks ago I installed high lift rocker arms on my vehicle along with a custom made intake insert that allows much better flow at high rpms.

A few days later I got a p0106, scanned it and the freeze frame info showed no misfires or any type of lean condition, just incorrect BM pressure in the manifold.

I removed the intake again, noticed coolant had leaked from the LIM and caused the gasket to warp due to me rushing and not noticing the o-rings from the old gasket were stuck on the intake plenum. Coolant also ate away a small area of the intake insert and it didn't seal properly, basically there was a gap between the upper area of the plenum and the cast runners of the LIM.

Grabbed a new gasket, took the old insert out and replaced it with the plastic intake runners that were installed from the factory. During the test drive P0401 came up, and p0106 was set as a pending code.

I'm still noticing a variation in idle speed after the car has run for a while, and I know I have no hoses lose because everything has been double checked. I'm hearing no hissing, no hesitation when driving not nothing. Idle only changes by 50-100rpm, the needle just goes up and down ever so slightly. Also noticed gas mileage wise I'm losing about 20 miles per tank. Other than that the engine is running perfectly.

Anyone have any idea what could cause this? Both codes point to a vacuum leak but I'm having a hard issue finding one.

Answer 1

P0106 Manifold absolute pressure sensor Performance

P0401 Exhaust gas recirculation (EGR) flow insufficient

What is the fuel trim? especially at idle lifting the rocker this would make the intake valve open late and close early it would cause the exhaust to open late and close early. So the vacuum leak would be internal of the engine.

Here is a fuel trim that is showing a lean condition.

Here is a good fuel trim

Use a vacuum gauge to see where you are at idle. With your vehicle there is nothing wrong with the MAP sensor, this kit just put it out of range to control its performance. and with an EGR that coded an insufficient flow, this means that the vacuum for the intake is low and by having a low intake vacuum throw the timing off and puts it in a retard position