SlowLS400

I've been a long time lurker on CL and it has been a great asset being able to refer back to CL for troubleshooting tips and resolutions. I have run into a problem that is kicking my a** with my 93 LS400 w/ 190k miles.

Whenever I accelerate from a stop or slow speed, unless I FEATHER the throttle gradually up to desired speed, the will buckle VERY bad and will not accelerate at ALL. In fact the RPMs will continue to drop dramatically as if I let off the throttle. As soon as I let off the throttle and re-apply it very gently it will not go anywhere. This is not a transmission related buckle/ hesitation, definitely without a doubt an engine related issue. It has become so severe that I dont consider the vehicle safe to drive.

Here's what I've done so far reading up on hundreds of threads.

Replaced the spark plugs.
Replaced the wires.
Replaced the coils.
Re-grounded the engine with more sturdy cables.

Replaced the ECU with rebuilt units and checked with another good used unit.
Replaced the TPS with two good used units.
Cleaned the TB while still mounted with TB cleaner.

Have purchased seafoam but at this point think it be a waste of time and effort.

I have read hundreds of threads here on CL and have come to the end of the internets to no avail. I have seen COUNTLESS of threads with EXACT same problems but absolutely NO one has addressed this issue in its entirety. I'm very comfortable working on the vehicle and would be considered an advance user (many rebuilds, tons of Toyota product, lots of mods and upgrades under my belt) so if you can suggest it, I can do it but I would like to keep this thread going to obtain a definite resolution.

Another tid bid, as of today the ECU is throwing a code 41 (TPS) issue, and I will be correcting that issue in the next 20-30 minute adjusting the TPS within spec. Besides that there are no other codes. I also dont think this is fuel related as I can drop the gear and cruise at 5000 RPM without issues.

Saashraf
ps sorry for the long post but wanted to be concise.

python

iTrader: (4)

one of the bad things about this and other forums is that a lot of the threads that get started because people are having problems with their car and they dont follow up, meaning if and when they get it fixed they dont post what was wrong with it,this actually hurts others who later on have the same problems...fix the cel and reset the computer,drive it for a day or so and make sure the light doesnt come back on

damon

Tad shocked to not see the Air Flow Meter on your list?

ourbudd

I have only owned one for a bit but I have had a similar problem with a Ford van I had, tried many things but it ended up being the fuel pump, I tested and the pressures were good but when I went back to that I put the pressure gauge on and extended it so I could see it when I was driving and when I would drive it and it would stalll down the pressure would drop well below what it takes to run. I replaced the pump and the outer screens were plugged. I had the car for 3 years after that and had no problems. Good Luck

SlowLS400

I have infact swapped the AFM electronics with another unit from my GS300. The electronics are the same but the body on the LS is bigger. The AFM body is in mint condition.

You know someone else has suggested that same exact thing to me but I dismissed it, I figured it would cause a somewhat gradual hesitation and not such harsh. Did the RPM steadily keep dropping if you gunned the accelerator??

Saashraf

ourbudd

It when I took off from a stop sometimes woujld just about stall out, other times it would do ok. Not really what I expected from fuel pump but with fuel injetion if the pressure isn't enough it wont push through the injectors with the pressure in the cylinders etc. Hopefully you can get it resolved soon, things like this can be frustrating.

Nohawk Lex

iTrader: (5)

start the car and remove your TPS plug. If there is no change (RPM drops, surges or stalls) then there's your problem. If not, there's probably some TB cleaner still in your intake that needs to be burned up. Just my 2 cents.

JimsGX

SlowLS400,

Does this occur more often when its warmer out and tend to go away when the weather is cooler? Have you noticed if it occurs more frequently when your fuel level is below about half full when its hot out, or in cooler weather below 3/8 or 1/4 tank?

damon

SlowLS400,

I feel your pain, but to a much lesser degree,My 94 LS is suffering in much the same manner.
I swapped AFM's but have not gone as far as you have with TPS & ECU.

How far do we go before we start looking at injectors as the culprit?

johnslee

I got the same problem with my sc400..while at "P" or "N", I can accelerate up the 4000rpm easily...but the car seem to speed up very slow even when I pressed hard at the gas padle in drive. it's sound very loud too like I have a leak in the "cat". I can see a little steam came up from the back engine wall on the driver side after few miles drive..someone suggest me to clean up the injector..I tried the chevron injector cleaner..replaced the fuel filter and plugs..I am still looking for the solution!

johnslee

I believe it's a ignition coil issue..I will replace my this weekend..will let you know the outcome!

johnslee

PROBLEM FIX!!!! I replaced both the ignition coils today..the problem went away! the drive smooth as normal! thanks guys!

THXpro

I have also had this issue recently with added symptoms. Accelerating SLOWLY is no issue but give it some pedal and it bogs down and bucks like a mule, then (when I let off the thin pedal) the CEL light comes on followed by the TRAC OFF light. they rapidly both go out and no codes are saved.

I changed the fuel filter and the issue went away for a couple of weeks. I had noticed some extremely fine light brown dust in the fuel filter but it did not seem blocked. no idea if its performance was affected by this under load and full fuel pressue.

all symtoms started again 2 days ago, I had thought about the fuel pump but have been spending time reading the shop manuals and this forum for better ideas.

94 LS400

damon

I am kicking out an intermittent CEL 2526, lean code.
Think that I might try new coils as well.

JimsGX

JohnsLee,

Are you still trouble free after a week?