92 sc400 major bucking under light throttle
 

Just wondering if anyone has had probles with their sc400 bucking under light throttle. It's pretty bad at times and other times it's not as bad but noticable. I've already replaced the ignition wires, throttle sensor, plugs and fuel filter, all very recent and not for this issue. If i run the car wide open throttle the symptom doesn't appear, it's only under mid to light throttle and it's not speed sensitive. It does feel a lot worse when the converter is locked but it also bucks/surges when the converter is unlocked. I was leaning toward the igniters but i figured the igniters would cause the problem at wide open throttle as well as mid throttle???? If i disconnect the MAF sensor the ecu goes into failsafe and the engine runs well no bucking-swapped the MAF sensor (Air flow meter) out of another vehicle and same issue???? Fuel pump ecu???
Any help would be great.
Thanks for looking,
AJ

Just for kicks and giggles i replaced the ignition wires again (parts warranty) and still same issue, this is nutz. It's def. an ignition skip/buck caused by either the coils, ecu, ingiters or the cam and crank pick ups. Jermeyp111 has a 92 i'll swap the igniters and ecu out of and see how that goes...
Alos i bypassed the fuel pump ecu and still same symptom :cry:

Has Anyone Had Problems With Their Cam Or Crank Sensors?

im having the same problem mang....

you said when you unplug the maf sensor that the car runs well and there is no bucking/hesitaion??? Where is the maf located???

funny thing is that it is not noticeable all the time and will heasitate/bucks only when starting from a stop.

i to would really want to get rid of this problem.

The MAF is located on the air box, it's aluminum with a black elect. unit on top. There is one connector going to it with 5 wires. Unplugging it will send your computer into "failsafe" or :limp home mode". In failsafe the ecu don't look at most sensors, it reads onboard memory to keep the engine running. If that clears up the problem the next step is to track down the sensor that is the culprit. If my vehicle were OBDII the diagnosis would be a hell of a lot easier.
As of today i've tested all cam and crank senors-all okay (but may have int. failure). swapped coils-same, swapped igniters-same, swapped MAF-same, New ignition wires-same.

I fear i may have an ECU problem or intermitant crank and cam sensor failure. i believe the cam sensors are only looked at by the ECU in closed loop but i'm unsure as my Alldata will not give such info :cry: . If anyone knows the list of sensor the ECU don't look at in open loop that would be real helpful...
AJ

i see, when i did remove the maf clip from the airbox the car had no hesitation whatsoever!

so your saying that a sensor is the culprit to the hesitations??

I have the same problem on my SC400, but it only bucks at exactly 40mph, no other speed, and its not real severe, just enough that you feel it, it feels like I'm pushing the throttle and letting off quickly and repeatedly. Also it only happens every now and then, maybe once a week or two.. Never bothered me enough to try to figure out.

-Minh Tran

hey wicked did you try cleaning the maf on the intake its held on by three small screws, i took it off and cleacned it around the base where its rubber because there was quite a bit of dirt near it, after cleaning/replacing the hesitation wasnt there...

I've been suffering with this problem too. It happens on a '95 SC400 with 245K miles on the odo.

The problem is most noticeable when driving at 40-45mph and the engine is at 80% of the regular operating temperature. So, it happens when the engine is almost at regular temps. It DOES NOT happen when the engine is hot; only when the temp gage is between the first and second hash marks on the temp gauge. I am guessing that at this temp, the ECU shuts down the cold start injector(s) so the engine is running leaner.

Like the other members have mentioned, the hesitation does not happen if the engine is under acceleration

I have tried, without success:
Replacement factory spark plug wires
Caps and rotors
Running on 91 octane juice
3 cans of Seafoam (in the manifold, tank, before oil change)

I'll be replacing the plugs next, but I am not hopeful.

Since I also have a problem where the engine stalls at idle when the AC is switched off, I seriously thing the ECU has crappy firmware programming. If only it could be flash programmed :sad:

Is the check engine light coming on? Has anyone taken their car in to get it checked out?

Yeah... has anyone attempted to pull any error codes from the ECU? A car i'm looking at has this same problem...

the car isnt throwing any codes or cel lights.....but thre is definately something wrong...

I would say Lexus dealership $125 for diagnosis, I think you get a loaner for the day and a free car wash