xzaticah

its a 94 sc400 with 155k miles. Just recently picked it up. so i havent had it long enough to have any kind of history with it.

there is a 2 part question to this:
First: it never would fire up right away. it would fire one of 2 ways. 1 let crank for several seconds, like long enough to were you would wonder if it will even start. or 2, crank it for a few seconds, let sit for a second or so, then crank again and it will fire.

so i assumed dirty fuel filter, worn out fuel pump. i did the fuel pump first. it made it run better, but did nothing in changing the starting situation. so next fuel filter.

i installed the filter, but before starting it i washed and degreased the engine bay while i had it up in the air. so go to start it- still same starting situation but now it will only idle normally for a few seconds then will idle like poop. around or at 400 rpms. pressing on throttle doesnt really do anything other than maybe dropping the rpms more and even dying.

let is dry out for about a week just incase under the cap was wet. but to no avail. same start problem, will idle great for a few seconds(4-8secs) then idle bad. cant get it up the driveway because adding throttle makes no difference. meaning, can not make the engine rev up.

any help on one or both of these problems would be absolutely great. thank you in advance.

O. L. T.

iTrader: (17)

Please use the proper forum. Moved.

mikevandam

iTrader: (3)

for the idle issue : check MAF, IACV, TPS and maybe injectors.

xzaticah

Is there a way to check these without replacing them?

xzaticah

unplugged MAF pigtail from the sensor, started it and it did all the same exact things. press on throttle and would not rev up. just kinda of died. could it be this? would a normal running sc400 do the previously described when the MAF is unplugged?

Bankswood

Could be Fuel Pump ECU. Do the Fuel Pump ECU mod and see if that helps.

I know I always seem to offer that advice but I have a 93 SC 400 that had all kinds of starting, idle, throttle problems and the mod fixes it all.

xzaticah

I will indeed give that a try right away and will report back. thank you very much.

xzaticah

that did help with the with the hard start issue, so the fuel ecu is probably going out or is bad or whatever. but thats not really the concern now that i know what can be done about it. thank you again for that advice.

so now it starts pretty good and idles well. so im assuming that we could rule out the IAC valve as being a problem. also would it be safe to assume that is not an injector issue seeing how it does fire up and idle fine.

it idles fine, but when i push on the gas pedal it sounds like its loading up and wants to die. At no position of the gas pedal will it rev up, only bog down and sputter.

im really only wanting to replace whats not working, so would the TPS make it do this or a MAF??

xzaticah

I ruled out the MAF or the volume air flow meter. tested good. both ignitors and coils are good.

i have not tested or checked the TPS. if for some reason that checks good would anyone have any ideas what this problem might be? so still on the hunt...

SC400slide

iTrader: (11)

What about vacuum leaks? There could be a broken vacuum hose lying under the TB that is disconnected or cracked.
Test the TPS with an ohmmeter. There is a DIY thread on here somewhere. GL.

xzaticah

all the vacuum lines looked good. didnt noticed any cracks or anything seperated. i changed out all the plugs and wires cap and rotors. the previous plugs were black and wet. the new stuff made no difference. although the cats get really hot i now noticed and the new plugs are black as well. so its just dumping fuel.

to recap: it fires up right away and will idle awesome for about a few seconds, or until i press on the gas pedal and it will just start sputtering and idle around like 300 RPMs and it wont rev up, as in can not get it to rev past 500 to 600 RPMs. just sputter and pop and like backfire.

still trying to figure this out.....

SC400slide

iTrader: (11)

Then I'd do the fuel pump ECU bypass. Could be that, and also could be a faulty ECU. We shall see soon enough. GL

xzaticah

the fuel pump ecu is indeed good. i have been researching many many hours online as well as under the hood. im starting to think it might be the ECU. i have read up on the capacitors that go bad, but none of that jell is leaking out anywhere and there are no burn marks of any kind on the boards.

is there anything more a lexus dealership could do to check this? I found that thread on the hesitaion issue and how to check basically everything.

with how wet the plugs are, is it possible that all the injectors are staying open??

SC400slide

iTrader: (11)

...which would make sense if it's that fuel pump ECU. Get that bypass done and report back!

xzaticah

it made no difference.