SC400slide

iTrader: (11)

You know, the ECU is still there...random issues like this point to ECU. At least it will be rebuilt, if anything.

emLEX

Yeah, trust me, it's still on my mind. I just emailed Tanin inquiring about the service but I don't think they do it anymore. There is nothing in the ECU repair tab on their site and I thought I read somewhere that they're not offering this service anymore.

Any other recommended vendors to have this done?

TaninAuto

Reason it is gone is because we are on the fence about doing ECU's anymore. We have rebuilt many with great success and praise. On the other side of the fence we have done ECU's where people still have issues after getting it back and cause us all sorts of negative public relations issues.

We cannot diagnose a vehicle over the phone or internet.

We have even went as far as replacing ECU's for three individuals recently and then they say, "well I'm still having the same problem. Guess it's not the ECU, sorry".

In short, we want to help the community and continue to provide this service, but not if it affects us negatively. We still will do ECU's on a case by case basis.

emLEX

Well hott damn. I was changing the oil yesterday and taking a look at things while under the car I notice a ground wire that isn't connected. It's the one right behind the oil filter. Found a nut to replace the one that was missing and reconnected it. It made a huge difference overall, but it didn't completely fix the problem. Strangely, the hesitation now is intermittent. When before I was always able to replicate it every time, I can now only get it to do it about 25% of the time. My next step will be to go through all of the grounds and make sure they are good and clean.

t2d2

iTrader: (8)

Interesting find. If that made that much of a difference, I would start by cleaning that particular ground again and adding some dialectric grease. I suppose it's possible you have multiple bad grounds creating the same symptoms, with one significantly worse than the other(s), but it sure sounds like you identified the bug but didn't fully squash it.

emLEX

Yeah, it was late last night when I did this and already dark out, so I didn't clean it or anything. The next step will be exactly what you said, cleaning/greasing all of them, and replacing if need be. Considering the fifference it made, I'm fairly certain doing this will remedy it for good...hopefully.

On a side note, I also felt a considerable performance increase after this. Before, flooring it from a stop wouldn't break traction. I originally attributed that to the sticky 265 Michelins, but now it will spin them(it, it's still an open fiff) pretty easily. Drivability, overall, is imroved, mostly.

t2d2

iTrader: (8)

I have 245/45 summer performance tires in the back, and I can break traction at maybe half throttle. I'm not sure how that compares to your rear grip, but it sounds like you're back around the proper power level now.

leaderpvp

Hey, bringing the dead back from past.
How have you ended up?

93sc400nm

I have this exact same problem hesitation only after warm up just before 2000 rpm but intermittent. No codes.

I did have the ECU rebuilt but in no way am I saying the rebuilder didnt rebuilt it correctly...just was not the problem at all. Replaced ignition coils, plug wires, cam sensors {when I did have a code 13}, fuel filter

Did you end up fixing it? I am going to double check my grounds after reading this thread

leaderpvp

mostly, but i know where the problem lies now.
First my low rpm is not related to the engine, it is tacho faul showing lower 😉
the hesitation was related to ? Haha, clogged egr, iscv, throttle body, we also replaced vacuum lines which was "wooden" already 😅
it fixed the hesitations, mostly it came from clogged throttle body.

t2d2

iTrader: (8)

I tend to forget to mention vacuum lines, since that's something I automatically do with a used vehicle with old, crusty lines.

emLEX

So, long story short, not long after my last ost about this the car got put away and not driven for over 3 years. A couple of weeks ago I decided I missed it and brought it out of hybernation, only to be reminded of this on going issue.

It's difficult to recall exactly how the car felt back when it was put away, but I sort of think it's as bad as it was before finding the loose ground wire. So, I'm back to where I started.

emLEX

UPDATE: Been reading and reading and reading...came across a few threads discussing similar issues to mine that talked about the EGR valve as the culprit.

Unplugged my EGR valve last night, and what do you know??? No hesitation, car runs great.

Apparently, it is really common on 95 1UZs, which mine is. It can be a problem on other years, but there is something specific about the 95s. Unplugging it did cause a Check Engine/TRAC Off light to appear, so I'll either be doing the resistor trick, or taking the valve out to clean it to see if it makes a difference. Maybe I'll just delete the EGR system all together.

Unfortunately, I'm leaving town for Thanksgiving, so I won't be able to drive the car until the week after to really be sure the problem has been found, but it certainly appears so as of now.

Also came to realize that I may have the wrong TPS in my car, although it seems to function fine. I have 89452-33010, but Toyo DIY shows that for SCs up to a 7/94 production date. Mine is a 12/94, and the part number should end with 22090.