Working on a 93 e 150 van with a 4.9 staight 6,cold start it run's ok at best but when it get's to temp it has a irratic idle(600 to almost 1000 rpm,s)eventually will stall.Repaired several vacuum leak's including a new egr valve.Code 181 come's up on the scanner for rich fuel limit.I cannot find any other vacuum leak's externally.No fuel coming from the fuel pressure reg. hose.Unplugged the o2 sensor to see if it was shorted but it does not make a diff.Any suggestion's?Been a GM tech most of my career so not really famaliar with this system.Van has almost 200,000 miles on it.
Tim

Check fuel press. The early 90's 4.9 had regulator issues. if pressure is over 45 psi, replace regulator

? alldata 45 to 60 psi normal,running the van this morning and it ran at bout 52 to 54 psi.

My bad, Ford manual says 45 - 55 psi running. Let it run a little while with gauge on and see if psi builds

Does not,let it sit for hour or so and it did not bleed down.Reading snap on fast track bulletin's it tell's map sensor problem's in this era.looking there next.Plenty of vac to the sensor......run's better unplugged with vac line plugged off.

If it ran 200k with many vacuum leaks possible cat. conv. plugged. Any easy way to open up exhaust and check it? maybe just take out up stream o2 and see if it runs differently...

Thought that to Mopar,found a cat test on how it works.com and test was normal.I suspect ecm at this point.Waiting for customer repley.

Idle control sensor.

If it runs better unplugged, that generally indicates a faulty map sensor.

-Maurice