06 Celica 1.8 VVTI common vaccum leak locations

[WezP]

Just wondering if anyone on here knows of any common locations that vaccum leaks occur on these 1ZZ-FE engines. 

My Celica seems to be running a little rough and using more fuel than it used to. So I plugged my code reader in and found a pending lean code, also the long term fuel trim is sitting at around +18 when increasing RPM this normalises. 

I suspected a vaccum leak so I plugged the intake and bit weird but I blew vape into one of the vaccum hoses and couldn't see any leaks. I then put it back together and sprayed easy start all around the intake manifold and all the boster lines etc. No change in idle and no reduction in fuel trim. 

I'm now suspecting a possible exhaust leak between the manifold and the 02 sensor although I would have thought there would be a loud noise that would accompany this if it were bad enough to change the fuel trims that dramatically. 

Before I go down the route of looking for an exhaust leak I wanted to know if there are any common causes of vaccum leaks on these engines I can investigate.

FYI 02 sensor voltage is fluctuating normally and MAF sensor is showing 1.7-1.8 gps which is normal I believe. 

Any help would be appreciated

[CAPTAIN SOLO]

Was the code P0171 system too lean?

Engine running rough is usually caused by air/fuel errors.

Check the air filter and airbox to make sure they are secured tight, all vacuum hoses are plugged in to the right nipples.  I had a P0171 in a Lexus GS300, wasted a lot of time looking for leaks.  Turned out the air filter was placed in reverse, so it let too much air go through.

Check the plugs.  Make sure they all burn evenly and brown, not having black or white residues and are gapped right.

A bad MAF can cause a lot of problem.  Clean it out with residueless contact cleaner. But sometimes a clean and electrically tested MAF can still malfunction.  Swap in a known good MAF from a Toyota or Lexus sedan.  They use the same DENSO MAF.