OBD won't communicate with low and rough idle

Hi, I'm brand new to the forum. Hoping to find an answer from someone else that was able to find a solution to my same problem.

I've got a '98 3.4L 4Runner with 276k miles. It's been running fine up until 2 days ago. Went to start it on a hot evening and immediately I could tell it was idling low ( about 5-600 rpm) and rough. Put it in drive, drove for about 30 feet and it died. Same scenario 2 more times. I then decided I'd try and start it a 4th time and it idled fine, drove it 20 miles home and it was like nothing ever happened. Started it the next morning and it drove fine another 20 miles. After work, it started up and I drove a few blocks to the store and turned it off. Twenty minutes later, came back, started it up and it idled roughly and died in drive like the night before.

Limped it one block to a mechanic and he checked for vacuum leaks but couldn't get either of the scanners to communicate with the OBD( although there wasnt a CEL). I left it there and he cleaned the MAF but it didn't seem to help that evening. The next morning he started it up and drove it around quite a bit and it seemed fine. He was able to communicate with the OBD but everything read normal, no codes.

Thinking it might miraculously be fixed I picked it up after work and soon as I started it the same problem was repeated. He came out and plugged into the OBD but no communication with his scanner. He checked the grounds to the ECM but all indicated fine. He seemed pretty knowledgeable and said his best guess is a bad ECM because when the problem occurs there is no communication with the OBD. He said he has not seen this type of thing happen before.

Forgot to mention that every time the problem happens there is some pretty heavy, visible exhaust so it appears the fuel mixture is pretty rich. After we talked I was going to limp it back to work but it started up fine and I drove it 20 miles back home.

Sorry for the short book but has anyone had this problem and fixed it??? I hate to replace the ECM on an educated guess!

 

Could be a loose or frayed ground, the ground above the No.2 cylinder will cause those symptoms.

 

I think you just confirmed my suspicions Yoda. Last weekend I got to the ECM to take it out and look at the manufacturing stamp on it because apparently there are more than one to choose from. A guy at work had said " make sure its grounded good to the chassis". So at the same time, I took the neg. off the battery, replaced that terminal, and cleaned up the ground at the chassis. Started it up and it ran fine. Took it on multiple short trips that weekend - no problem. Drove it all week for work - ran flawlessly. So unless I'm missing something here, I think it's been healed... Thanks much for your input!

 

I love happy endings.