pepo289

Hello, my 2009 maxima has rough idle, though good acceleration or no problems on WOT.
i used a scan tool, and it shows +10% on Long term fuel trim for bank 1.
when i hit the gas pedal, LTFT goes to normal ~ 0%.
LTFT for bank 2 is 0%

Want to do the smoke test to find any vacuum leak if present, but the VIAS valves are closed, even if i pushed the lever on the valve, its really hard to throw smoke by the Vacuum tube.

Any help appreciated.

CorollaULEV

Hey dude - I just went through this very same thing on mine for different reason. I replaced spark plugs which required upper intake manifold removal and I did NOT replace the intake manifold gasket. It caused a rough idle and long-term fuel trims to go way up. Mine was on both banks, though because it was leaking all around.

So the smoke test....never tried it but seems like a good idea. I do not think the VIAS (power valves) are your problem, though. What makes you think this is your problem?

What I did was to use a butane torch - just turn the gas on (without igniting obviously) and spray some butane around where you think the leak is. Keep in mind that it takes a couple seconds to cause a change at idle, but WATCH those SHORT TERM fuel trims. The short terms will bounce around quite a little normally (even on a perfectly running car without vacuum leaks), but you should see a change when you have located the leak with the butane. As it sucks in the butane, your short term fuel trim will drop some. To get an idea of what you are looking for and how long it takes, direct the butane nozzle directly into the intake snorkel at the front of the car above the radiator. On older cars, you look for a jump in the idle speed to tell you that you've hit the jackpot. The newer ones are too smart for that - you won't notice much a difference in idle, but you will see a change in the short term fuel trims. It will be a BIG difference when shooting butane into the intake snorkel (mine went to -19% from +6 or 7), but when directed at the vacuum leak, they only decreased from 6 or 7 to around 0.

Also - I'm not sure why you think it is the VIAS valves?? Bank 1 is the front 3 cylinders and bank 2 is the rear 3. The VIAS valves aren't set up to control one bank per VIAS valve. The VIAS valves are in the plenum - before it actually splits into the individual intake runner.

My guess - you're looking at the intake manifold gasket. If there were a leak at the VIAS it would be where the VIAS valve is mounted onto the intake plenum, not the vacuum hoses. If you trace the vacuum hoses on the VIAS valves, it leads to the solenoids, which in turn feeds into the manifold vacuum chamber (weird circular disc thingy on top built into a kind of triangular shaped part of the plenum). You check for vacuum leaks by yanking the vacuum hose off while engine is off and it will make a "ppssshhh" noise because it always stores vacuum, even with engine off. If there is a vacuum leak in ANY vacuum hoses, anywhere then you won't hear this. The ECM supplies voltage to the VIAS solenoids to actuate the power valves when RPM are over ~4000rpm to open them. Vacuum is applied to the power valve over 4000rpm to open them and this definitely would NOT cause a change in your long-term fuel trims at idle. Otherwise, there is no vacuum and they remain closed at any rpm below that. I do not think this is your source of vacuum leaks.

Like I said - the VIAS valves themselves aren't plumbed like that. It's not like power valve 1 goes with bank 1 and power valve 2 goes with bank 2. The power valves both operate in unison and do their work in the plenum before the air splits off into bank 1 (cylinder 1,3,5) and bank 2 (cylinder 2,4,6). Hope that makes sense.

The FIRST places I would look for leaks would be the upper intake manifold gasket. After a number of miles, that gasket gets very thin and worn out. It's really odd that it would start leaking randomly without being messed with or taken apart.

After that, I would look at the lower intake manifold gasket - again really odd if it started leaking without being messed with.

Anything else would cause your long-term fuel trims to elevate on bank 1 AND bank 2 because everything else is plumbed into the plenum before the air splits off into the individual cylinder runners.

As far as your LTFT going to ~0% when you hit the gas pedal - that's because your vacuum changes. Vacuum is highest at idle. Vacuum leaks ALWAYS are worst and cause worst symptoms at idle. Vacuum is lower with foot on the gas. Mine ran no different - it was ONLY at idle that I had a problem. New gasket totally fixed the problem.

What kind of scanner are you using??

Hope this helps,

Trav

pepo289

so bank 1 are the cylinders facing to the radiator?