I've been battling with these codes for a while. I only have the Torque Pro Lite OBD scanner, but is shows my mixture is between 17.5 and 18.
* I recently had my bad O2 sensors replaced, which started this issue. (perhaps it has always been to lean and I didn't know it?)
* I have replaced my MAF sensor, intake plenum (with new gaskets), both the part-load and full-load breather tubes, brake line vacuum line, and MAP vacuum line.
* I have removed and cleaned the throttle body and replaced it with a new gasket.
* It seems to be running fine, no misfires and plenty of power. It does run a little hot, about 208 degrees.
* Many times I have tried the test of spraying carb cleaner around key points and hoses, but cannot hear any changes in the engine output. I cannot find any leaks...

Is there anything else that might be causing his issue?

 

You won't always hear anything but if you watch the STFTs they'll change.

But first have you check you do have a leak? (Engine hot, park, watch LTFTs at idle then rev to about 2500 and watch again.)

In case your tool won't do this - get one that will! Much cheaper than what you've already done.

 

Good idea, my TorquePro is nice, but it is limited in function. Thanks

 

If you are running out of ideas, best is to do a smoke test, i.e. inject smoke in the intake under slight pressure, and see where it comes out. You can have the test done at a shop, buy a smoke tester, or even make your own. These testers generate smoke by burning mineral/baby oil and allowing for influx of compressed air (1 psi?) and expel thick white smoke. The fuel pressure regulator has a vacuum line that is great for smoke injection to the throttle body. You can make your own with an old soldering iron burning baby oil on a rag, and a bicycle pump for cheap.

Other suggestions:

• dip stick o-ring
• EGR accordion pipe, if you have EGR
• ALL the NORMA connectors have o-rings that can be replaced
• Any oil leak likely is an air leak, too (valve covers, etc.)
• Brake booster line brass fitting o-ring
• Oil filler cap
• Line to the purge valve
• Line to the fuel pressure regulator
• etc.

 

Thanks FMertz! good info.
I do have an oil leak in the front pan, didn't think of that...
I will also check the other items you listed.

 

I haven't seen it mentioned yet, but, is your intake tube cracked? Remove it and check the accordion section and the Hemholtz resonators. These are the most likely to crack due to age and heat. If there is any holes in your intake tube you have an air leak that is the cause of your P0171 and P0174. This may be a good time to upgrade to an aluminium intake tube.

 

Thanks, giandaniel
I had purchased a new intake tube along with the new MAF sensor and new seals. Seems to be ok there.

 

+1 on doing a smoke test - I made a tester since I am cheap - paint can, a couple of quick release air couplings through the lid, pressure regulator from an old propane grill to connect to the air compressor, some tubing, and burning incense sticks inside the can. You can knock one up in 20 mins if you have the bits and pieces lying around. Of course you need to cap the intake with something when you do the test.

 

Just wanted to update the post, I did finally find the issue in the part-load breather pipe. I couldn't do a smoke test, but on advice I went about spraying some carb cleaner in different locations. Finally under the throttle body (driver's side) I did get a reaction from the engine. I dug down into the area and found a break in the breather pipe where it joins into the plenum under the throttle body. Apparently, the prior owner had tried to fix this break by slathering epoxy all over the pipe, which finally broke down. (This is not the first issue I've corrected from the prior owner taking the cheap fix)

But all is well! Fuel trims back in line, no codes, and the engine is breathing normal again. She loves me.