93 Dakota likes to stall, runs rich

Maintenance/Repairs
1

I have a 1993 Dodge Dakota with a 5.2l MPFI and auto trans that has me and many other mechanics stumped. Recently it stalled on me when I pulled it into the driveway, and ever since it has had this problem.

When I start it up in the morning and it’s cold, the problem isn’t as bad, but as it warms up it gets worse. It sounds like it’s running rough, but its firing on all cylinders. I’ve verifies this by pulling the plug wires and also the fuel injector wires, and each one will bog the engine down a bit. Also, when I’m cruising or parked, if I hold the throttle at 1000 rpm or less, it loads up and will stall when I let off the throttle. I have to bump the throttle to about 1500 rpm or so when pulling up to a light so that it won’t stall on me. When I hold the throttle and it loads up, I can read the o2 sensor with a scanner and it shows 0.8 or 0.9v, so I know it’s running rich. If I let off, the sensor reads normal. It’s not super rich, but enough that it causes this problem.

Things I’ve tried so far:
Replaced plugs, wires, cap, and rotor
New coil (old one had cracks in the case)
Checked distributor for play in the shaft, timing chain for looseness, and cam sensor for damage
Has a new PCM, swapped back to old one and the problem still exists
Checked fuel pressure with and without regulator, is within specs cold or warmed up, no odd drops in pressure
Checked all sensors with scanner to verify they read within specs
Replaced all sensors with known good used AND new and none made any difference (o2 sensor, MAP sensor, TPS, air intake temperature, idle air control, coolant temp sensor)
Plugs are brown/tan colored, none are blatantly rich
Replaced the battery, alternator, and checked all grounds
Checked the EGR system for correct operation
Checked for vacuum leaks and broken wires, found none

The truck also has no catalytic coverter and only has 1 pre-cat o2 sensor. I also am not getting any codes.

Any ideas? I’m at a loss.

2

What is the MAP value at idle and vacuum gauge reading? What is the fuel trim value at idle (short term and long term adaptive memory)?

3

Your description of the actual problem is pretty vague. We have some rough running at idle and some occasional stalling letting off the throttle. (I also don’t know what it means to say it “loads up”). Is this truly only an at idle/low idle issue? You said it “sounds” like its running rough. Can you describe that better?

Check the compression before you go any farther with anything.

How was the coolant temp sensor checked?

What exactly did you find when you checked the fuel pressure with and without the regulator?

Clean the IAC valve & throttle body.

4

Vacuum gauge read 20-25lbs at idle with no fluctuations. The other stuff I’ll have to check when I get my scanner back.

It sounds like its running rough like it’s not firing on one cylinder, except that it is firing on all of them. Almost the same sound when you have a lopey cam installed. It used to sound much smoother. It sounds like this throughout the whole range, but it gets excessively worse at idle, especially when holding the throttle at or below 1000 RPMs, which is when it is getting way too much fuel and “loading up”.

The CTS was checked with the scanner and replaced with a new one to double check, it made no changes. The truck also goes into timing mode once the sensor is disconnected, so it is working right.

The fuel pressure was in the correct range with the regulator connected, and when the regulator was disconnected, the pressure rose a bit like it was supposed to and again was in the correct range.

IAC and throttle body have been cleaned multiple times.