YotaTech Forums - 1994 Truck Engine Miss and Code 31 22RE

Hey all, I have been lurking here for the past few days reading up on codes and what not to get a grasp on a particular problem with a friends pickup before starting on it. Lots of good posts here so I thought I would contribute.
After repairing his timing chain cover from the typical damage due to t-chain guides last year, and then a headgasket 3 months later it has been running great with the exception of a strange miss that caused low idle and sometimes dying at stops. Milage 192K with 22RE engine.
I test drove the unit and I could feel that it had great acceleration but when on the highway at cruising speed I noticed what felt like the ignition cutting out about once every 8 seconds just briefly for a split second. When the engine is warm and you come to a stop sometimes it would try to die if you didn't keep your foot on the accel while holding the brake and clutch pedal down. Once again this was intermittent and didn't happen at every stop. I changed out the fuel filter which wasn't all that bad (and it was pretty plugged) despite some of the posts here about it. However, I used to be a Toyota forklift technician for 6 years before going to work for CAT, and I too was surprised to see Toyota mount the filter in a rather "unserviceable" location. I still love Toyota products due to the dependability, and the thought that goes into design. Just a brief story...when I was with the Toyota forklift dealer we were sent to regular schooling, and after they trained us on a particular model they would hand out documents regarding a different model forklift that they were planning to redesign the following year. They asked 'us' mechanics to write down anything we thought they could do to improve the current design regarding servicability and the like. I always thought that was very cool! :banger:
Anyway back to my original post.
The fuel filter was plugged quite a bit and improved the power overall but the low idle/dying problem was still there.
Fortunately the truck was running like crap when I pulled it into the garage and I bumped the idle a bit to keep it alive so I could check for vacuum leaks and the like. It was sporting a code 31 which I cleared, then check that it was cleared, restarted, and it recoded the same number again.
I started the engine again and was spraying carb spray around the intake to check for leaks and I leaned on the intake plenum where it says "EFI" cast into the aluminum. The engine smoothed right out and ran great! I removed my hand from the manifold and it started to shudder again. I thought..a I applying enough pressure to the manifold to actually seal up a loose intake gasket? Well after extensive checking and retightening of all the intake manifold bolts the problem still existed. Ok I could see the engine rock slightly when I applied pressure to the manifold so I was wondering if there was maybe a cracked vacuum line that was only open in the rested idle position of the motor, before pressing on the manifold that would move the engine enough to seal the cracked line up? So I checked al the vacuum lines in the area by the manifold with no luck. I did start wiggling wires and hoses and found that I could also clear the problem up that way but I just couldn't narrow down the culprit. Finally after 3 hours I realized that I could move the wire loom close to the #1 injector and the problem would go away. I also noticed when it ran poorly that if I pulled plug wires from the distributor cap theres was no one cylinder that was failing on it's own...but seemed like they were all crapping out in unison.
I tore into the loom just below the battery where it leaves the chassis and suspends over to the mount on the intake manifold by the #1 injector. I was sure that this was the problem area but after cutting open the loom could not find the exact wire causing the problem. :bang: But by still wiggling the loom I could get the problem to go away. So I thought to check the loom where it leaves the engine and travels over to the cowl by the EGR valve. If I moved the loom up here it would also clear the problem up. Since the problem seemed to affect all cylinders I started with the main loom that travels the back of the firewall over to the igniter. Checked the igniter connector which looked good.
On the way back over to the maniflod on the same loom I could get the problem to clear up more frequently, at which point I noticed the loom was laying on the EGR tube. When I reached in to pull the loom up away from the EGR tube the problem went away! I pulled the loom back away from the firewall and could see where the heat from the EGR tube melted through the tape, convoluted tube and into the insulation on a green wire with a white stripe exposing the bare wire which was intermittently shorting to ground via the EGR tube. To verify this I grounded a test wire and touched it to the bare green/white wire. The engine ran like crap instantly! After repairing the loom I cleared the 31 code and it hasn't returned. I also noticed someone had re-taped the loom to its plastic clips that hold it to the firewall..but in the wrong position. I could still see where Toyota had originally taped the clips on, but this re-taping by someone down the line moved the loom over closer to the EGR tube. I cannot verify this however until I see another loom on a similar truck that hasn't been messed with. Here are some links to pics of the short. Can anyone verify what the green / white stripe wire supplys in the grand scheme of things? I don't have a wire diagram for the truck.
http://members.cox.net/scrid/toyotawire/01.jpg
http://members.cox.net/scrid/toyotawire/02.jpg
http://members.cox.net/scrid/toyotawire/03.jpg
http://members.cox.net/scrid/toyotawire/04.jpg
Hope this might help someone down the road. Thanks everyone, this is a great site for info!