scott101

i have a 1993 lexus sc300 5 speed manual, all original car with the exception of a welded differential and 18" is wheels.

Occasionally, when I am driving in a straight line, my car will begin to jerk forwards and backwards. usually it is for about 2 seconds or so, jerking several times during that time period, and then I will usually shift to try to stop it. It has happened in every gear from what I can remember. (from 1st - 3rd, ive only been driving around town lately). Im not sure what could be causing it. It has happened between 2k rpms-4krpms, and I havent really taken it above that.
I really havent tried anything yet. I guess I will go back through the back half of the drive train and make sure everything is fully tightened, although Im pretty sure I re-installed everything well after the differential was removed. Im nore sure if this is a common problem but I havent found anyone else with the same problem so I thought id ask.

thanks for the help

topdog849

iTrader: (1)

replace the maf sensor and tps sensor and have it calibrated right

1JZPWRD

iTrader: (59)

I second that. Its usually one or the other or a combination of both. GL, keep us posted.

1uzSC

BAM who needs diagnostics when you own an SC.

2JTsc300

i also have a 93 sc300 5 speed and mine is doin the same thing but it runs fine once i start it up on a cold engine, but if i turn it off and start it when the engine is hot it bucks like that. i think its the MAF or even the ECU. im about to install my AEM EMS and remove the MAF and install a MAP sensor so i can start my dizzy delete and go NA-T. if it stops bucking once i delete the MAF and ECU ill let you know. it wouldnt hurt to send the ECU for a rebuild either. im goin to do that so i can get anther sc300 and swap it to 5 spped for a DD. GL hope you figutr it out

scott101

thanks for the help everyone. I agree, the more ive read on the internet it points to a issue with the ignition system, so i pulled in intake apart and pulled the plugs but they all look pretty new/ clean, so I dont think thats it.


this is exactly what is happening to me:
which leads me to believe that it is not the ignition system because it works well when cold. I will investigate the maf and ecu and other things. the previous owner said that a new ecu was installed, so hopefully that isnt the problem

and do let me know if that fixes your problem. at this point, I am just going to try everything based off peoples recommendations

sj408

iTrader: (6)

Its your TPS bro... replace it and send me a beer.

Especially when you can drive the car forever but as soon as you try and turn it off and restart when warm it bucks.

I had a brand new tps on from toyota and it took me about a year to figure that one out a while back..... logic told me that a new tps shouldnt be malfunctioning but as soon as i got a datalogger it was clearly apparent

i literally drove my car 850 miles without turning it off.... drove great until i turned it off and re started

scott101

alright, thanks for the info, that will be the first thing I replace. can you just put in a new one or does it need to be calibrated the way that people were mentioning above?

I took the intake apart to check the plugs, I checked the first two (looked very new and clean) decided that wasnt the problem, and put the intake back together. I drove it for a while until it was all warmed up, then I wasnt paying attention and stalled in a parking lot (embarrassing I know,) and i started it back up about 1 second later and it ran fine on the 5 mile drive home.

Im sure it is still an issue, probably with the tps, but is it true that the jerking it can appear on and off like that?

thanks for the help
scott

sj408

iTrader: (6)

yes sir, those are the exact symptoms of a bad tps. sometimes works and sometimes doesnt.

I would advise to calibrate the tps properly (search that one) but until you have time to calibrate it you can just install it in the same position the old one was in.


only reason im so dead on sure is because i dealt with this issue for a year, oh and go oem toyota tps... dont bother with your local parts store one. It will work but it will fall out of calibration very quickly.

SC400slide

iTrader: (11)

Don't hesitate replacing the TPS The Throttle Position Sensor went out on my SC, and I had the same jerking, bucking and surging. For a brand new TPS, $40 bucks or so. Like 1992Lexus said, (now 1JZPWRD) keep us posted. Post what issue was when solved for future reference!

2JTsc300

I just picked up my car from my tuner ad had my aem ema, map sensor and iat sensors installed. An my car was doin the same thing. He had an extra maf for my car and he tested it and my maf was bad causing my jerking like u were saying. He was deleting my maf anyways but I told him
About ur problem and he wanted to help figure it out. So it's not always the tps cause my problem was the maf

sj408

iTrader: (6)

you obviously had a different problem with different symptoms... probably similar but this just screams tps especially with the fact that when he starts the car and drives at first its ok but when he turns off and restarts the problem comes out.

2JTsc300

thats what mine did, i put that in my first post

scott101

I am definitely going to replace the tps now and calibrate it and see how it goes.


do you mind providing a link or something to where you got it for that price?

thanks
scott

scott101

i got 2 sensors out of a 1992 sc300. one was on the throttle (TPS) I believe, and the other was on this secondary throttle thing inline before the actual throttle. Not sure what it is. Anyways, both the sensors look identical, have the same part number, but they have different white numbers on them. They also look slightly different to the TPS in my 1993 sc300. will they work? should I give it a try?
thanks
scott

will put up pictures and part numbers in a bit