1996 p0171 and p0174

I’m getting a p0171 and p0174 lean codes. I also get p0430 cat system efficiency below threshold. The cat code has been present for a few years now. I have checked a few basics. Fuel pressure is good. I’ve sprayed intake cleaner all around the intake looking for a vacuum leak. Ran through some of the trouble shooting until I get to the point of needing better scan tool to control switches and sensors. I know that the intake manifold is the most common for the 99-00 years but mine is a 96. I have looked through the tsb’s and I don’t find the same tsb called out for the newer models. When I erase the codes they don’t come back right away. It may be a day or a week. Any suggestions?

Clean the MAF....do a search on MAF in this forum....as I have listed detailed instructions several times.....

There is also a air temperature sensor in the flex hose that can be cleaned in the same way.

You will need non-residue electronic cleaner.....you can get it at radio shack.

Make sure that the tube that goes from the crankcase oil breather to the flex hose that goes from the air cleaner / MAF unit to the throttle body....is intact and correctly seated at both ends.

Make sure that the PCV valve is correctly seated in the rear valve cover.....and that the grommet that the PCV valve seats in is good.

Also verify ALL the hoses and connections in the PCV valve to upper intake manifold line are good.
In particular, verify that the elbow on the top of the upper intake manifold does not have a crack in it.....mine got a crack on the inside of the elbow.

Please take note that there are a LOT of vaccum lines that tap into the PCV vaccum line......and a leak in any one of them is a problem.

Also, make sure that the oil dip stick is correctly seated in it's tube. The air that flows into the front valve cover (through the breather) is measured the the MAF.....so any air that flows into the crank case..that has not come through the breather line....or into the PCV vaccum line is air that was NOT measured......and is to be considered a "vaccum leak".

Catalyst efficiency is monitored by the oxygen sensors that are AFTER each catalytic converter.
Verify the electrical connections......an make sure that the wiring harness has not fallen onto the hot exhaust pipes.
Be VERY carefull with the oxygen sensor that is mounted into the rear of the rear-most catalytic converter......When I was changing my Catalytic converters (all 1 assembly).....the mounting ring broke right out of the rear-most converter with VERY LITTLE turning effort. This would be a problem as that leaves you with a hole and no way to mount the sensor. All the other sensors mount into the pipes.

I think I may have found the problem. The rubber boot for the maf sensor wires at the bottom of the air cleaner housing was out of place. By the looks of it that would allow air to bypass the maf sensor. I going to give it a few days and see if the codes return.