After living the past few days under the hood of my 84 DL and getting a ROUGH IDLE for my trouble, I'm now entertaining the idea of just replacing the entire FI harness with a spare i have, but would first like the board's view before I step in it a second time. Please see my other excellent misadventure down a few posts titled "seein the blues." Just to be clear, I don't want to do this unless there's no other way. Prior to these latest procedures, car ran well with a slight hunting throttle when cold, especially backing out of the garage where it would either surge or stall. I attributed this to the IAC. Cleaning the old one was out since it was on its way out anyway. The larger problem was the completely trashed flame trap assembly that was spewing oil over the right side.

Specifics on what was done these last few days resulting in the rough idle:

-New injectors, fuel pressure regulator, IAC valve, temp sensor, battery, flame trap and hoses.
-Cleaned out the breather box, intake and throttle body, hoses and pipes as well as anything else within reach.
-All hoses tight and no leaks. New gaskets at throttle body and intake.

Recent 2006 work includes plugs, wires, cap/rotor, O2 sensor, cat converter.

I mention all this because work is being done on a nice rust free CA body I intend on keeping for a very long time, so parts I add are there for the long haul. There were many issues with this 240 when I got it and most have been addressed. Hope to one day reach the half million mile marker with her. She's currently at 275K.



OK here's the problem. She idles poorly and really smells nasty. There's a hard thump, thump, thumping sound and an occasional stumble when idling but it runs resonably well past idle. There is an occasional surge present and the Idle speed is now higher than it was, so I temporarily lowered it with the idle screw beneath the throttle body. The seats shake noticably. Exhaust isn't spewing but there was water dripping out the tailpipe along with dark specks on the garage floor before pulling out. I drove it for about 30 miles today and it drove well.

Here's what I did so far today to address rough idle:

-Swapped out both the ECU and AMM with spares, but no change.
-Visually checked plugs and they're all very nice looking...dry, clean and tan.
-Unplugged injectors and #4 has a less pronounced change when unplugged than others.
-Checked hoses and all look tight
-checked O2 sensor and it looks fine

I'm leaning towards a flakey harness since there were issues in the past with it and even had to repair the temp sender this time around. Tugging and moving the thing around could have shorted something in the loom.

Checked for continuity between injector4 (GN/W) unplugged and pin2(GN/W) in the ECU connector with BAT/neg disconnected and it was there. Problem is, it was not only there, but in every other pin of the ECU connector as well! If the harness were shorted how could it affect most of the pins?? I then did the same check on my spare harness (off car) and my 84 parts car with bad harness (in car) and they both only read between ECU pin2 and the other GN/W injector circuits. I can give you the specific pin numbers that came up buzzing on the meter if you feel it would diagnose this condition and point to a common origin to at least eliminate the need to swap out the harness.

It's not that I'm looking for the easy way out on this, it's just that I'm not proficient enough to diagnose this without help and would gladly accept any guidance to resolve this before I pull the rest of my hair out. thxx again and sorry for the extended verbiage.