So I have a 1997 ford f150 v8 4.6 2w
I got codes p0171 and 174 my truck seems fine till the idle drops it's weird when I have it on park it's fine if I turn the wheel left the idle drops when the ac turns on the idle drops and it's wasting crazy gas
Where should I start first in finding this problem?

 

A look at the code descriptions will tell you the motor is running lean.
A lean condition is to much air.
The Computer has shifted the fuel tables rich to account for the fault.
This why the idle and gas consumption is out of wack.
Find the air leak into the intake tract.
Look at the PCV hose rubber fitting in the rear of the vertical intake manifold as a start.
Good luck.

 

Yup, 171 and 174 means a major vacuum leak since it is both the left and right sides.
Usually a connection (or leak) somewhere on the manifold. Check the intake tubing and as said, the PCV hose elbow on the back of the air intake.

 

Spray some carb cleaner around the upper intake manifold and the hoses there. If the idle stumbles you have narrowed the area down to where you are spraying.

 

I've always done my own mechanic work and I've checked those hoses and changed them and it continues

 

I've always done my own mechanic work and I've checked those hoses and changed them and it continues

 

Does the HVAC inside the cab direct the air where you want? or does it just do what ever or is stuck in one position?

How do the brakes feel?? pretty solid or spongy? or do they fade if on the brake peddle for extended period? (long light)

 

I am having the exact same issue with my 5.4. I've read on other places that it could be the upstream o2 sensors are bad.

 

No, never. O2 sensors do not cause this code pair, they only report the condition.

This code pair is almost always caused by either an intake vacuum leak, contaminated or defective MAF sensor, or a weak fuel delivery system that is not delivering adequate fuel volume at pressure. 90+% of the time, it's an air leak and it's almost always the PCV system at fault. Once in a while, it will be a cracked intake manifold or gasket or, on some engines, the isolator bolts.


Don't bother, the computer is too fast most of the time and you'll never perceive any change by ear. However, if you use a scan tool and monitor either the short term fuel trims or the upstream O2 sensor voltages, one can see the effects of the enrichment fluid getting ingested and burned and this process will allow you to locate any intake tract leak (post-MAF).

 

Ya man the brakes feel spongy and loose

 

could be air in brake lines,But in your case... sounds like a good size vacuum leak , check the pre formed elbows on intake area vacuum lines, have had them split right open on the underside of elbow where you cant see them

 

It maybe that the brake booster is leaking. It may account for the vacuum leak codes and the soft brakes

 

My air filter can has a sloppy large rubber grommet on the bottom side for the IAT/MAF Sensor wires. It's in the right place for an air leak that can throw off the air/fuel mix to cause a lean condition.