Rough idle, misfire, dying at altitude.

'89 Cherokee 4L

When I'm wheeling at higher altitudes (Left Hand Canyon) my Jeep starts to run very rough, idles very low and likes to shut off at the most opportune times (going down a steep descent, idling while parked).

I'm told that it is most likely the MAP sensor causing this issue, the MAP sensor tube from the sensor to the throttle body is in good shape and both ends seal well.

Another person on the mountain mentioned that a high altitude MAP sensor would fix this issue however I am unable to find the part...I've only found a high altitude CPS sensor from Mopar.

Any ideas? Point me in the right direction?

I never heard of such a thing

Do you feel comfortable with troubleshooting electrical?

To a point. I've also replaced the cap, plugs and wires. It seems that I may just need a new MAP sensor that may be able to handle the altitude changes more efficiently than the one on there now.

Heat soak issue? From hot underhood temps? My 99' would do simiular to what your jeep is doing until I wired my electric fan to a switch and spaced the rear of the hood to help get the hot air out.

You might want to run a high altitude CPS. It will aid the power. It won't really do much for what you are describing.

So it runs fine when you are down the mountain? If so, I would look for a vacuum leak or a bad MAP. Check for a clogged air filter while you are at it.

I think heat soak wouldnt be a problem as my fan runs constantly with the motor and has a low temp thermostat...I could try spacing the hood. The air filter is new and it has a header & aftermarket exhaust for airflow...so I dont think that's the problem. The rig runs fine at lower altitude (Thornton area). Im really just hoping for the best with a new MAP sensor...if that doesnt work I'll try the HA CPS...then???

Yeah I'd have suspected the MAP as well. I thought they made a high altitude version of those as well.

There are threads out there about the high altitude CPS as well being used to fix this problem you're having.

First I ever heard of an HA MAP. I highly doubt it.