Wiring Harness Causing Surging Problems?

[Lexcelsior007]

I have been trying to diagnose a surging/hesitating/stalling problem on my 98 LS, 120k Miles. Bought in 2013 with 69k Miles. Bear with me as I'm close to finding the problem which seems wiring related. You can skip to the POSSIBLE CAUSE section of this writeup  if you want to know what my question and findings are. 

PROBLEM

I have a scantool (Torque) on my phone which shows the rich codes, Random misfires and catalytic converter codes on both banks (PO172/175, PO300-PO308, PO420/430). Problem seems intermittent and only happens when car is fully warmed up. As this happens, the Scan tool shows fuel trims go extremely negative on both banks. Half the time the car will start swinging lean (+ve fuel trims) and return to normal, then go negative again and then repeat this behavior. The car would wind down and surge back up as it goes from -ve to +ve trims. This is at idle. While driving the car would hesitate. Once in a while the car would just randomly die. Car always starts right back up no problem. 

TROUBLESHOOTING 

Things I have checked or replaced to remedy or as regular maintenance after problem occurred:

- Battery swapped

- Alternator replaced as preventative maintenance 

- Timing belt and water pump replaced 

- MAF sensor tested and swapped

- Crankshaft sensor tested and swapped

- Spark plugs replaced (routine service) 

- Valve Cover gaskets replaced due to oil leaks

- Fuel pump/regulator/filter replaced

- Fuel relay and resistor swapped

- ECU replaced / capacitors changed 

- Coil packs, fuses are in good working  condition. 

- Vacuum test and leak down test came out perfect (phew!) 

POSSIBLE CAUSE

None of the above fixed the problem. Now last week I started checking wiring integrity by trying to wiggle and induce the surging phenomenon. I couldn't. But once the surging started, I found that when I firmly tugged/pulled on the wire harness that's located on the rear driver's side of the engine, the car smoothed out and would start to run normally, every time! Now, there are like a few dozen wires in this harness that connects to ecu and ground points. The problem is the harness goes behind the intake manifold and I cannot get to them to check their integrity, unless I spend time to take out the harness. 

I'm guessing there is an intermittent break or wire fatigue in one or two wires that is/was caused by extreme heat in the area. So given the above information, what sensor wire would induce the symptoms I stated above? Since the issue affects both BANKS simultaneously, and the wiring harness is located on the driver's side, and I can't induce the problem but fix it by pulling on the harness only, I can rule out a few things. I'm thinking the bad wire would belong to either the Crankshaft sensor, Camshaft sensor, EVAP solenoid or something else. Or it's not a wiring problem and there is something else back there behind the manifold. Any ideas, guys? I'm so close yet so far. See attached pictures of the harness in question. 

Note: I'm not a mechanic and have limited knowledge when it comes to car repair but I learn quick and don't mind getting my hands dirty. 

[M.Yasir]

Hi

I have to say the engine bay is brand new! good job in keeping it that way

The list which you have mentioned about replacing/ checked is a big list, but before going into replacing parts, would you mind telling which OBD code reader you have? is it powerful enough to give you correct codes? i would advise you take scan codes from a shop, why i am telling this, i have a code reader (ELM chip) which in my opinion is not strong enough to pull out the codes that well, i have 3rd party software and connect it through my laptop bluetooth

Is there a check engine light?, the car hesitates... means is it having hiccups? like jerking? can you cruise exactly at 50 mph at tell the results? i had the same problem but for me the problem was spark plugs were fried i replaced them and the problem went away

Knock sensor maybe or maybe the timing belt replacement job missed out something

 

[Lexcelsior007]

Thanks. I have the ELM327 with torque pro app. The codes I get which is stated in the original post is PO172/PO175, PO420/PO430, PO300-PO308. I gave the car to the lexus dealership to diagnose and they didn't give me any new codes. The car would jerk while driving. Coming to a stop/idling it would start surging and may die if I don't give it gas. As stated in my original post, the replacements and servicing were done all after the first signs of this issue. This includes the spark plugs and timing belt so I would doubt it is that. Most parts were swapped from a friends LS so no cost to me. The fact that the issue affects both banks simultaneously indicates a sensor (wire) that overlooks both banks or could be 2 sensors from each bank that share the same bad/loose ground connection.

Nonetheless, ever since I started "fiddling" with the driver side wire harness (a week ago), the car has been driving relatively well, without surging and hesitating although the STFT's get around -14% everytime I slow down to a stop and then jumps back to 0% (normal). I have to look at the wiring for the knock sensor to test it. I just got the repair manual from ebay and am reading up on the proper testing procedures. As a start I have to test wire in that harness though.

I've uploaded a video on youtube showing a slow surge. It my surge faster than that as well.