Hanxious

Thanks so much for all the help on this. This is my last ditch effort before getting rid of the car.

So for anyone that's been following my threads:
https://www.clublexus.com/forums/gs-...ml#post9662612
https://www.clublexus.com/forums/gs-...ml#post9735481

I am thinking that the problem is with the ECU after finding a new symptom. Today I was having the normal symptoms, but got a new one...

When coming to a stop a coupe times, I noticed my speedometer was falling very very slowly. The reading was definitely off. I thought I noticed this before, but it was never as bad as today. The speed was clearly off. I'm almost certain it has said I was accelerating faster than I actually was when going up hill a few times also.

My symptoms come and go, and when they come, I have some or all of the following intermittently:
-Hard down shift into 1st coming to a stop
-engine vibration at a stop
-downshifts into too low of a gear after touching brake coasting downhill (Ill be at 4500 rpm and climbing and will actually have to press the gas pedal to get it to shift up)
-rpm bounce from a steady 1800 on the highway to 1000 and back quickly
-hard rpm drop when letting off gas (it jumps right back up after)
-abnormal shifting (too high of a gear for the speed) power loss
-and now this speedometer issue

I thought it could be various sensors, but with no codes coming up, I'm thinking its the CPU itself. (Could it still be a sensor without the trouble code?)

I've read about the downshifting issue related to the ECU, but has anyone else had more symptoms with the ECU? Does it sound likely?

Anything I should do or test prior to looking into a replacement?

Gs3500

Could be a combination of issues... carbon, transmission, MAF,??

Sodium

Are you using Techstream to look for codes, or just a generic OBD2 scanner?

Hanxious

Toyota said the only code in memory was a misfire code (I had one rough start in December on a cold morning. It almost stalled. It's started right up every morning since)

SILENTM

crank position sensor can cause some of those issues without setting a code

aristo1987

Camshaft sensor too

pbxcomm

I'm going out on a limb here..
You engine seems to be historically rich.. There are many perhaps related or unrelated symptoms, my thoughts are that starting at the simplest and working out may be the best solution.. Think about what you know to date not what you don't and don't guess the rest.
So, I know you mentioned you tuned the car.. I wrote here that 2 of 8 spark plugs I pulled from the package were not fit for installation. I've read here (and elsewhere) that after a spark plug change there were misfires and codes.. My point is, pull the spark plugs and check for damage, check the gaps for precisely .044, no plus or minus. This needs to be conformed prior to moving on. There is also a simple coil resistance check (while you have the plugs out) that will tell you if all coils are healthy.

Hanxious

The issue is the same, before and after, changing the plugs from IKBH20TT to FK20HBR11. Gap is good, I didn't check the coilpacks because I thought I'd get a CEL if one was going bad. I will test them the next chance I get.

The CEL has only come on twice since I've owned the car. Once for a misfire from a rough start and once was a P2198 (Before changing plugs and top engine clean). Both times, the light went out on its own and it hasn't been back on in months.

When it is running at it's worst, when I'm in 3rd or 4th gear, the rpm will slowly drop down to 1000 while accelerating. Crankshaft sensor makes sense, unfortunately its not an easy one to test.

I just fear replacing the crank/camshaft sensors and that not be it, then the ECU and still have problems $2000+ dollars later.

I'm just digging for any additional info (like checking the coilpacks) I can get, before I go down that road.

speedkar9

Engine mounts

Sounds like your in PWR mode

My GS350 does this. Even more so when cold. Its annoying but I think it has to do with torque converter lockup. My Solara also does this but its only noticeable if your looking at the tachometer.

Have you checked your transmission fluid, using the correct temperature with Techstream? Do these issues happen in snow mode, where the throttle map is more dulled? That could rule out a mechanical problem.

Hanxious

I originally thought it was mounts, but It comes and goes, so I listed it in case it could be connected with the other come and go issues.
No, not in PWR mode. Someone else mentioned that before, so I haven't used that mode in weeks, and it still happens.
Trans fluid was flushed recently at Toyota. I assume they made sure it was at the proper level. I haven't checked it myself.
Ill drive in snow mode for a few days and see if it happens there.

pbxcomm

Did you mention Techstream? Perhaps someone had here..
If you do not have it and you wish to continue, you may want to consider investing in the software. Go to autoprofessionals.org, become a member, they can set you up with the software.
Techstream has a real-time recording feature that allows you to record (in real-time) all engine data, as you drive, to a file, for future playback. If you go this route, I can send you the values of all engine sensors of live data recording from my vehicle for comparison purposes.

Hanxious

Thanks a lot, that would be great. Do you have a '06?

I haven't yet got the adapter and software because I don't own a laptop anymore. I was looking for used ones (because I only need it for techstream), but I think Ill just buy a new one, so I can finally look into this more myself. Ill let you know when I get it up and running.

pbxcomm

Glad to help..
I actually have an '08, but sensor values should be similar..
Techstream may be your only option from here forward. The last thing you want to do is "Parts Swap", this can become frustrating and not to mention monetarily budget breaking and you may not find the exact cause of the issue. You may find that what your experiencing may very well be a simple fix and relatively inexpensive, however, getting there may take more time and patience, but you will get there..
I'll send resistance values on crank sensors etc.. when I have a few moments.

Sodium

If you're going to put Techstream on a Windows 7 computer, keep in mind that it was designed to work on XP, so it takes a few extra steps to get it working on 7. I just installed it last week and I used this installation guide: http://www.ft86club.com/forums/showthread.php?t=73034. In case I forget later, the one error that I found was that the guide says to enter this in the command prompt:

msiexec /a "C:\temp\MVCI Driver for TOYOTA.msi" /qb TARGETDIR=c:\temp\mvci

The above didn't work for me, I actually had to enter this:

msiexec /a "C:\temp\MVCI Driver for TOYOTA.msi" /qb TARGETDIR=c:\Temp\mvci

Also, the guide is missing one important file, so PM me and I'll send you the installation files.

speedkar9

+1 on Techstream. Not only can you diagnose but you can change a lot of the personal settings.

Here it is on my old 4ES: