3rz misfire, stalling, running rich, comes and goes.

Hello, longtime lurker, this is my first post. Let me start off by saying, I have literally read every thread regarding a 3rz not running correctly across multiple sites, to no avail. My issue seems unique. Thanks in advance for your help.
1996 Tacoma. 3rz manual 4x4 207,000 etc. Truck misfires on all cylinders at random. Truck will do this for a couple days, not drivable, but if I let it sit for a few days the misfire will go away and I can drive it. 2-3 days of driving it comes back. When it does come back, sometimes it’s for 10 minutes, sometimes 30 seconds. It will run good for a few minutes, then run like crap a few minutes. It’s like there’s an off on switch for it running like crap.When the truck is running good, cel is off, scanner connects, no dtcs. When the truck is not running good, cel is illuminated, I turn it off, ignition in run, scanner will not communicate with ecm. If the truck is running good, I can unplug any particular sensor, cel will illuminate, scanner will connect and give proper code.

When truck is not running good, I can shut it off, put the ignition in run position, and the VSV on the intake manifold will go absolutely nuts, Switching on and off probably 15-20 times per second. So much so that the VSV will be hot to the touch. I’ve cleaned all the grounds, cleaned the egr and verified it’s function, checked for vacuum leaks, cleaned the throttle body, maf, iac, checked the tps, it has new plugs, wires, distributer. Pull plugs, all have carbon buildup. I’ve followed the harness, checked, wiggled, tapped, pulled on every connection. Cleaned pcv. Unplugged and plugged up everything I can find while it’s running good, cannot duplicate problem. Checked connections at ecm, took apart ecm, looks fine. I replaced the coolant temp sensor on the back of the head, which I was sure that was my problem as it broke when I put the socket on it. Not the problem. I haven’t done compression or checked valves. Only because neither of which would have intermittent symptoms. I do need to check my valves I know, but that’s a project for another time.

Also, if I shut the truck off while it’s running bad, put ignition in run, cel flickers on and off, it seems to be related to VSV going wild.

Sorry for long post, someone help me please.

 

So your scanner can communicate with the truck when the CEL is off, and not when it's on? What happens if you have the scanner connected when the CEL is off and it comes on? Does it lose communication?

The VSV issue seems to be critical here, or at the very least a really good starting point. Your symptoms sound to me like a classic case of chaffing wires. Something happens and a conductor shorts to ground/power or another conductor and the engine runs like crap. The very first thing I would do is, with the engine running correctly, get under the hood and wiggle every single wire. Not gently... put some effort into it. Pull/twist every harness and connector you can see/touch. Hopefully somewhere in there things will start acting up and you can narrow it down.

 

check ecm

 

?????

 

computer module under dash to see if its corroded

 

sorry not under dash under glove box

 

Good point - definitely a possibility, 'though I've found corrosion tends to be a more regular/constant issue. Easy to check and repair/rule out.

 

What codes, if any, does the CEL provide (I'm assuming you check them while the truck is running good)?

 

Hate when a thread dead ends at a question. This is identical to what I am dealing with. Was it the egr vsv or the ECU? Something is feeding power to my svs before engine cranks. If svs is clicking, then I cannot conect correctly to OBD and get no codes. If I can get scan before the vsv starts clicking then I get good connection. Codes are 401 402 and now 115. Which I clear. As soon as the svs starts clicking I loose connectivity to the OBD.