neagan

I've been attempting to solve the hesitation/ surge issue on my 95 SC400 for over a year now. Here is some interesting info from my local Santa Rosa, CA Lexus (Freeman Toyota/Lexus)service department:

Allegedly the 1995 SC400 had a bigger problem with this surge issue than previous years. Lexus started replacing the factory computers with a newer revised model that they came out with towards the end of 1995. There is actually a computer number difference between the two computers.

I havn't gotten the numbers from them yet, still attempting to solve other problems and it's taking a back-burner. Now I'll have to find a cheap replacement and see if that really does it. My SC really surges hard at 45mph when it suddenly descides to act out. I really didn't want to make a new car out of this. That's why I bought it to replace my ageing 88 Supra. What a bummer. It's still way more comfortable though to drive long distance than my IS300. Nitro

mserrano

Hello neagan, I've just recently joined Club Lexus and have been searching for a possible answer to my SC's hesitation problem. I'm curious, does your SC act up all the time or just under certain conditions? Mine runs absolutely great and accelerates smoothly when the engine is cold. Once it warms up, it hesitates and jerks out of a slow start or out of a stop. At highway or surface street speeds it accelerates smoothly. It's only out of a total stop or a slow acceleration after the engine's warmed up that it acts up. This has totally stumped the dealer. I've had it in the Lexus dealer shop twice, in fact it's in there now. Any ideas? One Club Lexus member suggested looking for leaks between the throttle body and the mass airflow sensor. More specifically, the tube that connects these two components has three connection points where the clamps can leak. He also suggested cleaning the pins on the sensor and the plug. I've suggested this to the dealer's service rep. and his tech. I'm waiting for the results. Any thoughts?

mserrano

neagan

This particular problem I'm having is definitely different from yours. What I and others have is periodically, when we're cruising along at around 45-50mph, just feathering the gas, our cars will suddenly start surging/bucking. If we accelerate it then goes away. 45mph just happens to be the speed many people cruise at between stop lights in town. For some, it's been an issue of the wrong type of transmission fluid, or not flushing the old fluid out correctly. (most of the fluid is still trapped in the torque converter), or by using aftermarket spark plug wires, rotors and caps that are cheaper. Many have actually had to replace the torque converter completely , which our SC automatic's get really happy-happy about it. It's like giving the car a cup of strong coffee.

The rest of us just keep scratching our ever balding heads. Your problem sounds like a small nightmare, althought the advise you've received seems spot on. Another thing to check is to clean the throttle body just around the butterfly. Especially on the Supra's this area can get up to an 1/16th inch build up of oiled crap that interfears greatly in the smoooothness of throttle response.

This is all part of the reason why our expensive cars are dropping like boulders in resale value. the diagnosis needed and the indifference of Toyota makes for an empty wallet for each mystery problem that crops up. It's actually cheaper to drive one of these into the ground and just buy a lower mileage unit. There's my biased ranting! Nitro

Nomis

This is the exact, and I mean exact, same problem I have - and others apparently. When it "bucks" it is most annoying. Apparently there is a Torque Converter Clutch and I believe that the friction material may be to blame. I don't know how the lock-up process works on this trans - possibly a spring or lack of sufficient line pressure is responsible for poor or partial engagment of the clutch?

Any ASE Transmission Master Technicians care to comment on this?

I'm still waiting for the time I get pulled over due to this. Officer, I have to drive 30mph or 60mph or my car gets cranky. I know it's a 45mph zone, but 30mph was just too slow...

Oh, the ETC Power/Norm button has no effect on the problem as it occurs only at part throttle. Turning off the O/D will keep the trans in 3rd gear and seems to help a little.

mserrano

I'm with you on that one nitro. I'd just like to find the solution for myself and then shove it up those so called factory trained technicians you know what!!! Acutally, those corporate executives "you know what" I'd like to shove my boot up. I've been dealing with Toyota since 1981 and have complained about the quality of their diagnostics since they tested a thermostat on one of my cars by putting a torch to it to see if it would open. The idiot trained factory tech welded it shut by doing that so he mis-diagnosed the problem as being the thermostate instead of the water pump, which shortly thereafter caused the engine to overheat, IN TRAFFIC, and left my wife stranded. I'm totally with you on that one bud!

mserrano

Nomis

I pulled the following after searching on google. This is for another car - maybe GM, but who cares I think this may be the answer to our problems. If this is it you guys are buying me a beer!! Looks like it may be the speed sensor. See my comments after the excerpt.

Excerpt form site:

http://www.salemboysauto.com/faqs/de...Action=Q&ID=28

" 2. As your are driving down the road, the computer is watching your throttle pressure, your engine speed, your vehicle speed in mph, what gear you are in and a/c operation. As you approach 38-42 mph, if you are on level ground, if you are feathering the throttle, if the engine is warmed up, if the car is in third gear, the computer will electronically lock up the torque converter inside the transmission which makes you have direct drive, so to speak.

On this day, the driver brings the car into a shop and complains the engine is bucking and missing . What is happening is the computer sees your throttle pressure stay at 32%, sees the engine rpms stable, but sees the reported speed at 36 then a second later the computer sees 43, then 38, then 41, then 37. The computer would be confused. How can the speed be fluctuating and the engine isn’t and the drivers throttle pressure isn’t changing either? As the speed is reported above 38 mph, the torque converter clutch (TCC) is locked and when the speed is seen below 38 mph, the computer unlocked and disengages the TCC. This rapid locking and unlocking of the TCC feels EXACTLY like an engine miss to the driver. But the computer THINKS the speed sensor is going wacky so it will set the SES light to tell the driver that it sees something wrong.

In this case, the speed sensor was replaced by 3 different shops, except the SES light kept coming on, the same speed sensor code was set and the engine bucked or missed violently when the speed approached 38 to 42 mph. Clearly, the speed sensor wasn’t the problem.

In this case, what finally fixed this car was when we pulled the speedo cable and lubed it. You see when the computer saw the speed vary, it was because the speedo cable was binding up, then releasing causing the speed sensor to report this "speed up, slow down" or 38-41-36-42-34-39 speed reading. Each time the reported speed exceeded 38 the TCC was locked, each time it dropped below 38, the TCC was unlocked causing the bucking or missing. You see, the computer can only guess on the repair, it really can not tell the tech if the speed sensor is bad or the wiring harness connection is loose or bad or if the speedometer cable is jerky and needs to be lubed. "

Now I don't think the speedo cable needs to be lubed in our case as it's probably electronic. Somebody help me out on this one, isn't there a seperate speed sensor that the trans uses for it's reference? I really think we're on to something here.

BLK13X

Things I'd check in the meantime...
1. ECU Resetting erases the memory from the computer, and starts a new learning curve.
2. Checked and replaced the sparkplugs recently? I'd change them for peace of mind. My car use to jitter when accelerating, it came down to the spark plugs needing replacing.
3. I don't know if checking your O2 sensors might be acting up? Who knows.
4. Check your throttle cable if it's nice and tight.

Just some simple things... oh yeah, I don't know but this could be a fuel pump or fuel pump ECU related problem?

Hope that helps.

Jose

neagan

Those are good/great suggestions; However, for those of us who have been dealing with this issue long term, we've replaced fuel pumps, done Lexus dealer diagnostics, Dealer tune-ups, checked for codes, ect. Several thousand dollars later, we end up with a Technician shoulder-shrug. Nitro

Nomis

So who knows about the transmission speed sensor? How does the trans guage vehicle speed? Where is the sensor located. These are the questions we need to answer.

VSsc400

iTrader: (1)

i did not know we had a sensor like that......

Nomis

I'm thinking the speed sensor is in the trans, maybe near the output shaft housing or maybe it's internal?
Does anyone have a factory repair manual to look this up?

BLK13X

my bad

Nomis

Don't sweat it, we can use all the help we can get. Thanks for the info.

Nomis

Any more suggestions?

One HoT

iTrader: (5)

I had the dreaded 40mph hesitiation....I seems to be cured, I haven't had hesitation for a couple of weeks now...Heres what I did to cure it...

-Replaced air filter
-Cleaned throttle body
-Reset ECU
-Beat the living hell out of the car

I got 220 miles to the tank recently due to aggressive driving...But, at least the 40mph hesitation went away...

I would check all of your air intake components to see if anything restricting air flow...

Good luck