96 Cherokee, Auto to Manual ECU/PCM swap question

I swapped in an AX15 into my 96 which had an AW4. I actually wired up a clutch switch to the NSS, so when the clutch is in, the park/neutral is closed, so it will crank, when clutch is out, nothing is closed.

This made it not CEL anymore, when I hard wired the park/neutral, it threw a CEL eventually saying bad NSS switch.

I also tried to hard wire park/nuetral and 3rd gear together, that also threw a CEL.

My issue is when I push the button to close the park/neutral, the idle actually changes. I had the car die on me once. When I was driving I hit the brakes and had the clutch pushed in, the idle dropped so much the car died.

So I wasn't sure if it was the clutch or the switch, so I tested it.

If I'm idling, in neutral, if I just push the clutch swithc, which just closes the park/neutral circuit, the idle drops to like 200 rpm, then comes back up. Sometimes it doesn't drop, and sometimes it drops and doesn't come back up.

I ordered a new IAC, but the ECU/PCM is for sure changing things with the idle when it see it go into park/neutral, and it's making the engine run worse.

What do people do about this? I got reverse and 4wd light wired up and working, but the only option is a switch I have to flip, then crank, then flip the switch back off? That is a pain.

I'm going to start another thread with a ECU/PCM swap question.

I switched my AW4 to an AX15 and I have some weird idle issues. I wanted to just track down a manual 96 ECU/PCM and plug it in and see if it fixed my issues, but my Jeep friend said I would have to change out the wiring harness. We tapped into the old automatic transmission harness for the neutral safety switch, hooked to clutch, the reverse lights, and the 4wd lights. How would all that work if I put in a manual computer?

I have read I could just swap computer, I shouldn't have to get a manual wiring harness right?

Anyone done this with some insight? I do need reverse lights and like the 4wd light, but don't care about having the clutch switch I installed work, only did it because I needed something so I could crank it with the auto ECU, but it's causing weird idle issues every time I push in my clutch.

The manual pcm has different decelleration fuel map values so say when you're driving in gear at 3krpm and then hold the clutch in or put it in neutral and let off the gas, the rpms won't drop past normal idle rpms. With an auto pcm in a manual, it will drop lower and or cut off. Find the manual pcm. I really don't think you need another harness.

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I have a 96 that I did the auto to manual swap in. I did the same thing with the clutch pedal switch and the neutral safety switch input to keep the check engine light off. The auto pcm does interpret the n/s input different and it affects the idle speed slightly. I haven't had any issues regarding this or anything else for the last 10 years and 50,000+ miles. A new IAC motor is a good place to start, as is a good cleaning of the throttle body. The PCM is very adept at keeping the engine running and will relearn the idle speeds quickly if everything is working right.


BTW, I merged the OP's two threads on this topic.

I ordered a new iac and know the throttle body needs a cleaning, I also found a manual pcm from a 96, same year, hoping it just also plugs in and reverse lights, and 4wd light still work. My concern was I wired those into the plug that the NSS plugged into, but the manual wouldn't have had an NSS, I am just hoping the wires go to the pcm and work the same, or sre wired the same. I know the manual had fewer wires and a different transmission plug

I wanted to report back. So I believe if you have a perfectly clean throttle body and IAC, it will compensate for you, but an auto ECU does work different. When you push in the clutch, if you wired this to the NSS park/neutral, it will drop the idle, trying to compensate coming out of gear in an automatic. It also does different things during deceleration, but it does work and drive.

I got a 96 manual ECU, same year, plugged it in, all the wiring I did for 4wd light, clutch switch, and reverse lights all just worked, nothing to change, all pin outs were the same.

It drives MUCH smoother now, idle's perfect and deceleration is great.

I will add though, running the auto ECU did show me my IAC is sticking a little and not moving as fast as it probably should, so I will be doing a throttle body cleaning and getting an new IAC, but a manual ECU is plug and play, and if you can get one, it does run better.

Thanks!