PO171 System Too Lean Issue

[OU1]

I did some searching on the forums for this issue and tried some of the ideas people had but have had little luck.  So here it is.  I have a 94' Lexus ES300 that is throwing the code PO171 (System Too Lean)  it's lacking extreme horsepower (almost as if it's in limp mode)  specially when im going up hills.  I've replaced the MAF and cleaned the MAF connector.  I replaced all the O2 Sensors, spark plugs, and fuel injectors.  I sprayed the upper and lower air intake with starting fluid in an attempt to hear the engine Rev but it did not.  The upper and lower air intake both have new gaskets.  This is where I'm at a loss and I'm hoping someone has any other ideas to try out before I throw in the towel and take it to a mechanic to have them do a look over.

[gbhrps]

ou1,

You've hit on your solution  ....... take the car to a good independent mechanic who is familiar with Camry's, the ES's baby brother. The solution is beyond your capabilities. A P0171 code has many things that could cause this issue.

Throwing parts and money at a problem that hasn't been properly diagnosed in the first place just doesn't make sense, as you've already seen in this case. Do some internet research for the issue, or see several knowledgeable mechanics and pick their brains before tackling any car problem.  When all sources concur on the fix, then go ahead with the parts route and DIY if so inclined, otherwise let the professionals deal with it. It will cost you less in the long run. Good Luck!

[OU1]

Well i replaced all of those items because they needed to be changed anyhow the car has almost 300,000 miles on it so I'm just sucking every last mile out of it, I've done a motor swap and transmission swap on it.  This issue arose after I removed the head and rebuilt it.  I appreciate your advice, I'll probably get it fully diagnosed.

[TrevC]

If the system is too lean then generally it is drawing unregulated air before the Lambda...check the exhaust joints and check vacuum hoses for even the slightest leak, holes, etc.

This can be proved by putting it on a gas analyser and measuring the oxygen level which should be 0% with Co2 at 20%....if not you have a leak somewhere.