My 87' dakota 5 speed with a 3.9l v6 and a carb has been running pretty rough since I bought it. It's okay once you get moving. Sometimes it will bog a bit and the power doesn't feel there, like the timing is retarded and occasionally it will just backfire and stall which is always fun in the middle of traffic. It is also hard to start after this.

The main problem is at idle though. Sometimes it's somewhat smooth and tolerable for a truck of that age but other times it feels like its got a horrible miss. It's like an intermittent vacuum leak. The engine stumbles and the rpms sound like they drop to a point just above stalling. The weirdest part is the oil pressure when this happens. It will drop to nothing on the gauge and if I give it some gas it will go to "normal" and then two seconds later it will go back to nothing. The oil pressure seems to hover a bit low in general too. When cold it's usually at the mid point when it warms up its just a bit over the minimum line.

The truck was sitting for a while before I bought it so assumed it was a hose or something but I sprayed some carb cleaner and couldnt find much. Not too good with carbs more experienced with fuel injection and obd2 so I'm on a limb here.

Things I've done so far:
Checked the EGR: If I apply vacuum to the valve at idle, the rpms noticeable drop so I'm assuming it's not stuck and its not clogged.
Replaced plugs and wires
New fuel filter
New belts
Put a vacuum gauge on it, it was around 15-20 in hg at idle. It didn't sway back and forth it just slowly seemed to lose and gain vacuum. It also flicked a small amount not more than 1 in continually.

Any ideas would be greatly appreciated.

 

Have you checked your timing?

 

No the only things I haven't checked are timing and fuel pressure (no timing gun) I took the air cleaner off yesterday. Checked the vacuum hoses once again, didn't find much. Played around with the PCV stuff. At this point it just began to rain. Put everything back together and started up the truck, it now would stall after a few seconds of running. Went back to try to see if I left a vacuum hose unplugged, double checked everything and still it ran horrible. Thought to myself whatever I touched most likely is causing the problem and left it for the night. Checked over everything again the next morning and still nothing. I had a job interview and this being my only vehicle I had no choice but to limp it there.

Got home and checked it again and saw a plug wire that was disconnected from the distributor. I must of knocked it loose when taking off the air cleaner. Oh joy. Put the wire back on after noticing the boot was too far out and the plug couldnt snap on right.

Still runs just as a bad now. Ugh, that was pretty stupid, really hope I didn't burn a valve or something. It will run on fast idle but as soon as it's off it clunks and stalls.
Here is a video of what it's doing now.

https://www.youtube.com/watch?v=XOMc...ature=youtu.be

Maybe I should add a compression test to the list.