I have a 1994 SC300 with 152K on it and for the past 9 months I have been experiencing a rough idle, occasional engine misfires and stuttering as well as random stalling out. This occurs usually when I have come up to a stop and I am idling there for over 20 or so seconds. If it does not stall out, it will hesitate upon acceleration. Unfortunately this all happens randomly and only one mechanic out of four has been able to duplicate it. On top of that, if the engine is warm and i restart the car, the rpm will rev up and down until it settles to a rough idle-usually I just restart the car until I get a normal start,otheriwse it will drive like absolute ****. The engine code that was thrown out was a MAF sensor and this was replaced but did not solve the problem. Spark plugs, spark plug wires, ignition coil and distributor cap and rotor were also replaced and the idle air control valve and throttle body were cleaned.

The next mechanic to take a look at it was convinced it was the fuel pump and filter and these were replaced but again, nothing was solved. This guy was a particularly unfamiliar with lexus ( he had the car for three days when he asked whether or not it was a straight 6 or a v-6 !!!) even though when I called the shop beforehand, the supervisor was adamant that they were competent with toyota/lexus models. Foolish of me to believe them but anyways, another check engine code was thrown out but the next mechanic to look at it could not retrieve it (the battery had not been disconnected either).

this has been a very troublesome problem and have heard that the fuel pump ECU on the earlier models of the SC300/400 commonly went out. On top of that the wiring on the left hand side of the trunk which leads to that ECU also have a tendency to go out. I've heard that pin connectors on Toyota/Lexus also get jiggled out of place easily and that could cause it. Has anyone has this experience? If so, does it sound similar to what I've described? I'm at my wits end with this car and with all of the incompetent mechanics who have looked it over!

 

Best thing to do is simply bypass the FP-ECU. Worst case, thats not the problem and your FP runs at 12v constant like 90% of the other SC's here on CL.

Its very easy to do:

https://www.clublexus.com/forums/per...tures-faq.html

 

Thanks, appreciate it

 

Try this:

https://www.clublexus.com/forums/per...rol-valve.html

Sounds like this may be your problem if your FP ECU is not bad.