I have a 92' sc300 with roughly 280,000 miles. It just started this yesterday, but only did it for a minute than stopped. Went to go to work this morning and the car is constantly doing it now. I start the car up and it runs fine, idles perfect for a few seconds, then starts to miss, BAD. What happened last night was i got in my car after work, started it, drove to the end of the parking lot with nothing wrong, then went to gas it to pull into traffic, and it had nooooo power. Was like i was in 4th gear at 20mph, then the car started hiccuping, i threw it in neutral, turned if off, and restarted it, and no problems all the way home (i have a 45 minute drive from work). Same thing this morning... went to leave for work, got out of my driveway, drove about 20yds and it started to lose power, i could put the pedal to the floor and nothing, RPMS would barely move, then put the pedal to the floor again and it would rev up, then RPMS would drop. It WILL sit and idle for about 2 minutes, but its a very rough idle, missing bad, i can sit in it and give it gas, and when i let off the pedal the rpms come down and it idles perfect for 5 seconds, then starts missing again.. please help me guys, i take very good care of this car, and i cant find nething wrong under the hood.. unless theres something im missing..

 

kinda sounds like its sumtin blocked out and not letting you go, then when u floor it again giving it more pressure it makes it go... id start with a cheaper thing and run a sea foam or sum cleaner through it to unblock things

 

fuel filter? fuel pump dying? bad plugs? bad cap and rotor? bad spark wires? could be anything.... have you done any maintanance to the car at all? when was the last real good tune up? has it ever had a the timing belt changed?

 

All maintenance is pretty much up to date aside from timing belt. Im a little over due for timing belt. But spark plugs, wires, everything else is kept fine.. I run nothing but your name brand fuels, chevron, exxon, shell, or texaco, so i dont have any crappy fuel running thru the car. Mobil 1 extended mileage 10w30 and a mobil 1 filter. I run fuel treatment thru it every once in awhile. I have a short ram Injen intake, i make sure thats all nice and clean and tight every time im under the hood... I mean to tell you how well i take care of this car and how much money i have in it, seats are leather and suede, headliner is suede, carbon fiber hood and roof spoiler, TSW rims, Tokico blues and Eibach springs, i mean the car is in fantastic shape other than my mistake of backing into another car a month ago but i cant track this problem down..

 

maybe a bad idle air control valve mine went bad but it didnt affect driveablity....just rpms wouldnt go down when in park...hmmm did u check already to see if anything was loose or unplugged i.e. spark plug wires cap n rotor ever changed? are u getting a check engine light?

 

Maybe a bad coil pack. Try jumping your fuel pump.

 

Yea. It was throwing code 24, 31, and 74. All have to do with the MAF. I wouldnt even start anymore. I just replaced the MAF. And its throwing the same codes, and the car still wont start. Yea everything under the hood is fine, I havent taken apart the throttle body and moved it yet to check the spark plugs of course cuz its a pain, but i just replaced everything 2 months ago, new wires and plugs. And it has been running fine ever since.

I will tell of a problem its had since i bought it tho. Every now and then when i go to start the car, it will start fine, idle fine, then a few seconds later RPMs will drop and the whole car will shudder at the lowest RPM and will sit forever doing that til it dies. Sometimes turning the key on and off a few times gets it going. So im thinking maybe a fuel problem?

 

Okay, i replaced the maf, unhooked and rehooked the battery, now its only giving code 78. Fuel pump control circuit failure. The MAIN relay is fine, so its kinda narrowed down to either the FP ECU or the fuel pump itself. I can test the ecu by taking the rear seat apart and basically bypassing the ECU to see if the pump is ok and its a bad ECU, but i just got off the phone with one of my good tech friends who worked at the toyota dealer here, and said in the 4 years he worked for toyota, he never saw a lexus ECU go bad.. So im kinda leaning towards buying a new fuel pump and seeing what happens, the pump has never been replaced. Soooooo.. i guess we will try that?

 

I believe I read the 300 doesn't have the trouble with the fuel pump ecu the 400 does because the 300 ecu doesn't vary the speed of the pump like the 400 does.

 

U could just do the 12 volt mod to jump the fuel ecu...then if it still persists then its prolly gonna be the fuel filter or pump...

 

Okay, just tested. My dad got in the front seat and tried to turn the car over while i listened for the fuel pump to click on, nothing. Even felt it, not even a slight hum. I unplugged the plug that runs the 12 volt wire to the pump, and checked it with a test light (btw just fyi, some people might know this but i didnt, power doesnt seem to be sent to the fuel pump until you crank the car. Unless im checking the wrong wire, but if my memory serves right, when i modded my license plate lights, the green wire was the wire that sent the 12volt signal) my dad had to crank the car before the light on my test light came on, so the pump is getting power. Checked the ground on the fuel pump with a meter, its fine. So uh.. yea.. any other thoughts?

 

This thread will detail the fuel pump ecu bypass procedure, not all of this will apply to your 300 since this is mostly a 400 issue but hopefully the bypass procedure is the same.
https://www.clublexus.com/forums/sc-...on-issues.html

 

Yea i had the same jumpers. Tried it. No go. Fuel pump. yaaaaay!!! Thanks guys. FatBrian that thread is awsome. And thank you other guys for helpin out. Ive never real dealt with the fuel system in these cars, never had a reason to til now, except replacing the fuel filter. Thats a load off my mind. Ordering the pump now. Thank you all again

 

Oh and brad thankyou for that helpful thread, i saw your the one that made it. I know its about sc400's, but it still helped me in the final diagnosis.

 

Hey no problem man. Glad to hear you found the issue. Give us an update when you get it going again.