Multiple sensor issues, won't pass smog

[Resartus]

OK, so I bought my 95 Ford explorer 4.0 limited 4x4 cheap, with a lot of issues I'm prepared to tackle, but I just can't get it to pass Oregon smog.
The short story:
Hydrocarbons and CO is high at idle, but just barely OK when revved (on 3rd test. Thankfully they don't charge for a fail)
Replaced plugs and wires
Replaced MAF and IAT sensors
Replaced ECT and coolant temp sending unit (the one with the single threaded connection)
Old EEV-IV codes KOEO: 111 for the immediate codes, then a 113 IAT above max voltage, and 157 MAF below minimum voltage.
Old KOER codes: 116 engine coolant temp higher or lower than expected
New KOEO code: same old codes plus 122 TPS below minimum voltage. Note this code appeared just yesterday

Yesterday, after seafoaming the engine is when I pulled the codes again.
I tested the MAF and TPS, according to an instructional page I found somewhere, and discovered that both sensors seem to be operating correctly, changing voltage properly with changing conditions. The TPS even survived and passed the tap-while-measuring test.

Also, the engine runs reasonably well for 250k miles, but there is a clicking under one of the valve covers(yes, I know. It's important to fix that really soon) and the engine won't hold rpms steady. It idles decently, about 600-700, but when I rev the engine to about 2500, the engine drops a couple hundred rpm and comes back, about 2 second intervals repeating, with my foot steady on the gas pedal

With all these sensor failures, I'm wondering if it isn't the PCM or wiring harness that's giving me all these problems. I replaced the temp gauge, because it was sitting below C, and the new one dropped even further when the engine was turned on. Now one thing I noticed when I was inspecting the truck to buy it, was the signs of rodents having gotten into the engine compartment - droppings and a chewed plug wire, which is why I suspect the wiring harness. And after reading the EEV-IV section of this forum, I saw a thread about bad capacitors in the PCM.

I'm wondering if anyone else has any ideas of where to go. My budget is extremely limited, and I really don't think it's the individual sensors, since I've already replaced the main ones. Since I probably have or can get the caps needed to replace the ones in the PCM, I'm going to pull and inspect that first

Update:
I've pulled the PCM and it looks fine. No bulging caps (everything is surface soldered) so I'm going to reassemble and do the relearn procedure properly. If that doesn't work, then I'm off to the junk yard again. Thankfully no PATS...

Update #2 :
After a conversation with a friends mechanic who wanted me to start checking the wiring harness for broken wires, I used a different piece of info he gave me and called the local Ford parts counter to ID the correct PCM for my truck. Turns out it was replaced with an incorrect PCM (they left clues, like the 2 retention nuts being different).
So off to the junkyard I went.
The last truck there I checked, which of course the hood was jammed, contained my prize. Almost a perfect match, except for the F5TF at the beginning. And REMAN on the label. Which means I got a (probably) slightly used remanufactured PCM for my truck. Put it in, did the proper startup, and drove 45 minutes home. During that time, the O/D light did not come on, as had been happening earlier. Got home, pulled the codes, and got 111 on the immediate codes, and, surprise! I got a 111 on the kept in memory codes. So off to emissions tomorrow to see what happens. I think I'll need to change the transmission valve body (still doesn't want to shift out of first unless I let the rpms drop) and replace the coolant temp sending unit - info center keeps saying check engine temp

Update #3 :
Failed emissions this morning, but passed this afternoon with no points to spare. Pulled the throttle body and intake manifold on a whim after the fail. Throttle body looked as though someone smushed an entire Kingsford briquette on the back side of the butterfly. Cleaned that, added some compression enhancer to the oil, took a 30 minute ride on the freeway and went to deq. Yay me.now I have 2 years to restore the engine and emissions equipment

 

[gatzdon]

You may want to get a decent OBDII reader and download Forscan. Forscan is free and will allow you to pull the extended codes from all systems on the vehicle. Could help you track down issues in the future.

Forscan also lets you read all available sensor values (that's what helped me track down the Engine Coolant Temperature sensor reading too cold, but not cold enough to turn on the MIL).

That said, on a PC, the Forscan is able to actuate some things on the vehicle and issue commands, but on the mobile phones, it's all read only.

 

[koda2000]

You may want to get a decent OBDII reader and download Forscan. Forscan is free and will allow you to pull the extended codes from all systems on the vehicle. Could help you track down issues in the future.

Forscan also lets you read all available sensor values (that's what helped me track down the Engine Coolant Temperature sensor reading too cold, but not cold enough to turn on the MIL).

That said, on a PC, the Forscan is able to actuate some things on the vehicle and issue commands, but on the mobile phones, it's all read only.

95 may still be/is ODB I.

OP, with 250,000 miles on your engine it may just be worn out. A compression test is the best way to measure the engine's overall health. That will test the valves, rings and cylinder walls. The fluctuating idle could be due to bad O2 sensors, vacuum leaks or intake manifold gaskets. Start with a compression test (S/B around 160 PSI in all cylinders with no more than a 10% difference between cylinders). If your compression is low, I wouldn't put more money into that engine. Also check all your vacuum hoses. If they're dry and cracked, replace them one by one as to not confuse where they go.

 

[gatzdon]

95 may still be/is ODB I.

OP, with 250,000 miles on your engine it may just be worn out. A compression test is the best way to measure the engine's overall health. That will test the valves, rings and cylinder walls. The fluctuating idle could be due to bad O2 sensors, vacuum leaks or intake manifold gaskets. Start with a compression test (S/B around 160 PSI in all cylinders with no more than a 10% difference between cylinders). If your compression is low, I wouldn't put more money into that engine. Also check all your vacuum hoses. If they're dry and cracked, replace them one by one as to not confuse where they go.

Sorry, missed that '1995' part.