Colossus

Yet another problem..

My '90 Cherokee doesn't idle too well. It idles around 300-750 RPMs while sitting in park, sometimes coming close to a stall. Renix 4.0 with an AW4.

Here's a list of what I've tried so far to fix it.
- new fuel filter
- new tps
- Searched for vac leaks, couldn't find any
- Searched for fuel leaks, couldn't find any
- Cleaned throttle body and intake manifold with proper cleaner
- New O2 sensor
- Cleaned IACV
- New spark plugs
- New spark plug wires
- New cap and rotor
- Fuel pressure test. Rail primes to 35 psi. Idling in park the fuel pressure drops to 30 psi. During the test I revved it up to about 2500 RPMs and the fuel pressure went up to 35 psi but returning to idle the fuel pressure dropped to 25 psi before returning to 30 psi at idle. Doesn't seem right.
- Tested MAF the cheap way. Disconnected it, idle went up to 2k. Reconnected, returned to the same rough idle.
- Tested IACV the same. Disconnected it, Jeep started up then immediately stalled. I'm going to assume that means those sensors are working.
- Disconnected EGR solenoid but no change. Possibly the culprit?

She runs very rich, black smoke comes out the tailpipe when revved up high. I suspect the poor idle and rich fuel mixture are related. But I'm no mechanic.

Thoughts?

cruiser54

Check the integrity of the line from the throttle body to MAP sensor.

Also, check the mechanicals on the EGR. Is it hanging open?

FWIW, your fuel pressure seems low.