Negative long term fuel trim causes

1996 Toyota Camry 2.2l auto
No codes.

Was wondering what the possible causes are for negative long term fuel trim besides sensors, fuel pressure regulator, injectors, purge valve, air filter.

hows your power steering i heard that bad p s switch can pcm throw trims off good luck

Power steering is fine

Its been a while. Can the topic be revisited

tmauldin wrote:

1996 Toyota Camry 2.2l auto
No codes.

Was wondering what the possible causes are for negative long term fuel trim besides sensors, fuel pressure regulator, injectors, purge valve, air filter.
 

Negative fuel trims mean that, without correction, the engine would be running RICH.
RICH conditions are caused by either too much fuel, or not enough air. In addition to what you have already listed, an exhaust restriction, a flooded charcoal canister, incorrect fuel/alcohol compensation, and valve timing can all be possibilities.

Are you trying to fix an issue? How negative are your fuel trims?
Since you have no codes, I would guess that it is less than 10%, which is normal and not a problem.

Its negative 25 percent long term with short term oscillating between 3 negative and 3 positive. I figure it's only matter of time before a p0172 gets set. I also noticed intake manifold pressure was .4 psi lower than what it was when fuel trim was in the correct 10 percent range. Vacuum is vibrating excessively from 19.5 to 20 in hg. When before it was 21.5 in hg steady.