sputtering hesitating sc400???

[is_250]

I've done a search and im pretty much stumped. Most of the threads I have read had told me to replace most of the items i've done already. So far I have replaced:

-fuel filter
-cap/rotors
-NGK plug wires
-NGK platinum plugs
-New ignition coils
-swapped ignitors
-seafoam treatment
-cleaned pcv
-lucas fuel injector cleaner

Bascially my car runs perfect in the morning. When its cool out for the first 20-30 minutes of driving it is flawless acceleration is smooth with no hiccups. Once the car gets warmed up it begins to buck, hesitate and stutter from 1k RPM to 2k RPM. It is extremely noticeable on light throttle, at WOT it is less noticeable and the car will pull all the way to redline. The problem only happens under load, if i rev in neutral the engine revs freely. If I put the car in gear and hold the gas and brake, it sounds like my car has a 2-step on it.

I have tried disconnecting the MAF, but the sputtering gets worse and will sputter while the car is in neutral trying to rev. Its really begining to irritate the crap outta me.

Added bonus: My car puts out alot of heat. I finally got to meet up with another SC4 owner and he also noticed my car puts out tremendous amount of heat compared to his car.

 

[Muzza_NZ]

stuffed temperature sensor.?

Check this thread: http://lextreme.com/forums/showthread.php?t=10456

 

[is_250]

is the cold start temp sensor the same as the ecu temp sensor?

i was thinking about just swapping them around, but the part is about $25 USD, so i'll probably just buy one and give it a try.

 

[spf_lexus]

Is250

I have a thread going on very similar symptoms my 1uz is showing. I have scheduled my local toyota master tech to only do the fix. I found out after I rebuilt my engine it needed a slight "massage" for the tps, throttle cable and most importantly the transmission cable. I am experiencing very harsh bucking from 1000-2000 and horrible mpg, with the obvious "smell" of a rich engine so after a month of this i finally got around to it.

I have a damaged transmission cable that is causing slack in the line telling the tranny to shift or lockup and it's more prominent going up hills. I set my throttle cable to spec and loosened tranny line all the way and "eyeballed" the tps and today was the 1st day in a long time the hesitation was gone on partial throttle. You might have a perfectly running engine that needs a small adjustment. the "bucking" can be one of 2 things. 1st would be a misaligned TPS that will cut off fuel when the air/fuel mix gets thrown off too much and the cutting of fuel can be very harsh. Second would be the transmission cable... if the line pressure is too tight/loose it will tell the transmission to shift based off incorrect sensors so in the end you get torque converter locking up at the wrong time. I have a 3000rpm stall so when mine bucks... IT BUUUUUCKS!! lol hope this info helps.


I just re-red and noticed your putting out a lot of heat, are you getting any codes on the dash?

 

[is_250]

im not getting any CELs and my MPG is decent. My most recent tank got 21.5 MPG mixed highway and usually i average between 17-20 MPG depending on my right foot.

Im truly stumped... I would think if my car was running extremely rich, i'd be averaging really crappy mileage. Also, my car runs pretty smooth at highway speed regardless of the temp or how long ive been driving.

Im going to try getting the coolant temp sensor and i've got an extra fuel ecu to try out.

 

[is_250]

well the coolant temp sensor was a waste of $25. Next up: Fuel pump ECU.

 

[spf_lexus]

since your engine revs freely in neutral and won't in drive i'd look at your transmission... your shooting blind buying parts on a whim and throwing money away. Try loosening your transmission cable all the way and see if it still studders in low rpm. There's no way your fuel pump is faulty... if ones going out it will hesitate at high rpm due to the increased strain and fuel pump relay your talking about rarely goes out.

 

[is_250]

since your engine revs freely in neutral and won't in drive i'd look at your transmission... your shooting blind buying parts on a whim and throwing money away. Try loosening your transmission cable all the way and see if it still studders in low rpm. There's no way your fuel pump is faulty... if ones going out it will hesitate at high rpm due to the increased strain and fuel pump relay your talking about rarely goes out.

I dont think its a tranny issue, but i'll give that a shot.

Swapped the Fuel pump ECU and no difference. Im gonna check the IAT on the MAF and see what the resistance is. Maybe its getting some screwy readings.

 

[is_250]

well, i tested the MAF/IAT and the resistance is a little odd. at 68F it should be 2-3k ohms, im getting 1.5-1.8. at 176F its supposed to read 0.4-0.7k ohms. when I heated the MAF with a hairdryer it read 0.6-0.7k.

Does it really matter if im at 1.5k ohms instead of 2-3k ohms?

i also tested the TPS from the test connector and its supposed to go from 0-8.0 volts when the gas is pressed. im getting 1.07 volts instead of 0, is this close enough?

 

[mr2crazybyong]

i had a similar problem with my 3sgte, and it turned out to be just a misaligned TPS.

 

[mr2crazybyong]

any updates on this?

 

[is_250]

any updates on this?

actually, i found a break in one of the coil wires which caused the spark to arc on a nearby ground. this caused the slight hesitation and miss at idle.

also making adjustments to the TPS helped a bit.

how are things in the PI?

 

[Smitherz]

I was invited to help a local mechanic shop troubleshoot an LS400 today and I worked on it for about 2.5 hours swapping out more parts and checking things over. Still the same symptoms as you have described. Very annoying and checking the mechanics database there are A LOT of other mechanics that have had the same problems!

It must be a wiring fault but I'll also be checking on that TPS the next time I give it another session. There is a LOT of heat in those stock LS400 engine compartments and it must just wreck the wiring. I know that almost any clip you decide to remove must be done with extreme care since all of the plastic breaks when you apply force to disassemble things.

Not fun but I'm pretty determined to help the poor soul that owns the car. :sgrin: Or maybe I should tell him it's a lost cause and offer him 500 bucks...