NOT!!! Well anyhow, over the last two weeks my truck [my baby] has decided to sitt on my parade. Started with a sporadic miss that gradually got worse to the point where I figured it was either water in the gas or a clogged fuel filter. Cold climate and filter of unknown age. Dealt with that thinking that it should be cured...WRONG! Now it is running worse than ever.
OK, pulled codes yesterday...
KOER
99
81
57
WOT gave a continuous solid feedback and after several minutes I was convinced wasn't going to change [and it didn't].
KOEO
Six slow single slow beep/flashes.
six slow beeps, six cyl code?
157, bad MAF... it burned out my CEL over 2 years ago, so that ain't it.
21
So I disconnected the battery to get new codes.This time I got ...
the same thing, except No 21 on KOEO this time, everything else was unchanged.
This engine is running like crap. Now what? I had also discovered a vacuum line that was off so I pulled the ground on the battery to reset code.
So where to next?

 

I'm not clear on which vehicle or the codes you now have, are these for the 94 4.0L???
In my book P0157 is for the bank 2, sensor-2 (down stream/after cat O2 sensor)
The P021 was for engine coolant temp sensor out of range during self test.

 

This is off my Mazda 4.0 So you are saying that it may be my O2 sensor? The truck bogs down when under load, the higher the gear the worse it is. My EEC I-V says 157 is MAF.

 

OK, so its for your OBD-1 94 4.0L, so yes the P0157 is for MAF sensor below minimum voltage, not for the down stream/after cat O2 sensor, so forget the OBD-2 O2 sensor code idea, that was my bad.

So disconnect the battery B- cable to wipe the corrupt KAM fuel trim tables, then try removing (so you can get to it from all sides) & carefully cleaning the MAF sensor with a non residual spray MAF cleaner recipe product like CRC, or Valvolene MAF sensor spray cleaner. One of the auto parts stores has the CRC MAF spray cleaner on special this month.

If the vehicle has just been driven, let the MAF sensor cool before cleaning it with the cold spray, then carefully clean it, being careful to not touch or poke its wire sensor with the spray wand. Keep it squeeky clean while it air dries & keep it squeeky clean on installation.

If it runs better, because the MAF sensor was dirty & seeing as how its only to see clean filtered air, look up stream to the air tube, air box & air filter, to determine why it got dirty & fix that, or your problem will return.
Typical problems are modified, damaged, improperly buttoned up air box, damaged, or poorly fitting air filter, the use of foam, or cotton gauze air filter, or over oiling them.

Then reattach the B- cable & if you have the auto tranny, go through the cold & warm idle relearn routine to prevent possible driveability problems. A forum search will turn the relearn proceedure up.

Some thoughts for consideration, let us know how it goes.

 

A closure of sorts. My #3 plug was fouled to the point where it wouldn't fire, period. New 12,000 miles ago. It had replaced a plug that was also completely fouled. So a problem with that cyl. I tried to run a compression test on it but was unable to get the fitting properly seated. It did show repeatedly 60lb of compression. The EGR gasket at the manifold had failed, and the blow-by was quite evident on it. I made a new one and cleaned the EGR at the same time. EGR holds compression just fine, so its diaphragm is ok. I cleaned the MAF sensor which did nothing, as I was expecting, since it hasn't worked for years despite repeated cleanings. That was $125.00 wasted on a part that lasted all of 3 weeks.
Anyhow, the truck now runs a lot better.

 

OK, so the #3 cyl has issues with fouling the plug. Is it oil, or carbon fouled????

Did I read your last post correctly, to say the MAF sensor hasn't worked for years????
The trouble code that you have for it is for low input, so maybe check its electrical connector pins & sockets for corrosion, loose pin/socket fit, damaged wiring, ect.

Good find on the EGR valve manafold gasket leak.

 

Pawpaw, when I replaced the MAF around 12,000mi ago it lasted for all of 3 weeks, money that could have been spent on a pair of tires. I'll go over the wiring again since there is a possibility I missed something. I put few miles on it since I'm unemployed and the wife drives it 20mi to work and back every week, with a once a month 40mi round trip to get things in the 'big city' of Marquette that aren't available locally.

 

OK, so you have MAF sensor problems & it sounds like compression problems with #3 cyl.

Again, is the #3 plug oil, carbon, or fuel fouled???? You need to determine whats going on with cyl #3, as that miss can cause the cat converter to over heat & destroy itself, if it hasn't already done so with those long road trips with it missing.

When you say the MAF sensor lasted all of 3 weeks, what exactly does that mean???
What have you been using to repeatedly clean the MAF sensor with???? Since the MAF sensor is to only see clean filtered air if it has been getting dirty, you need to look up stream to find out Why its getting dirty. If its PID input to the computer is low, you need to make sure the computer is feeding it the proper voltage & its PID output back to the computer about true air flow into the engine isn't corrupt for some reason.