Okay I have a 94 SC 400 My problem is the car idles fine at idle but when you press accelerator in neutral or in drive it runs extremely rough we emptied the fuel tank put in new fuel filter Change the spark plugs, spark plug wires, rotors and buttons and it still runs rough Of course when I say we this is my buddy who's a mechanic doing it in his shop. Also the other day before doing the spark plugs and essentially the tuneup that the catalytic converters we're getting cherry red. does anyone have any thoughts???

 

sounds like one of your coilpacks has gone bad, or you have a bad injector stuck open, or even a bad ecu. If both of your cats were glowing I would lean more towards the coil as each one runs 2 cylinders on each bank, so both cat's are getting alot of raw fuel when one of these goes out, which makes them "light up". If it was just one cat I would lean more injector but being an sc400 always check the coils first.
3/4 of the sc400 problems on here are one of the coilpacks failing so I would start there, unplug one at a time with engine off and see if you can start it and if so if it made any change in how its running.
If one of them doesn't make any change plugged in or not, then you found the bad coil.

 

+1. ........................

 

Ali, thanks for the post. Just got off phone with my buddy and he did the coil test and replaced a bad one and its running smooth. It should be running like brand new when I pick it up. Thanks again.

 

Doesn't the car have only two coils? I'd be surprised if the car could run at all with half the cylinders not firing...

My car needed one new one and I went ahead and replaced them both -- they're both 20+ years old so no reason to put it off.

 

Thats good news, you will notice it will be twice as fast as before

Basically toyota made the ignition system in the most reliable way they could on a distributor driven v8, by having 2 distributors with 2 coils instead of just the normal 1.
Each distributor run 4 cylinders, 2 on each side of the engine, and I think they alternate in firing order, so basically when you loose a coil the engine goes along as a 4 cylinder while the other 4 get washed down with fuel. The ecu should trip a check engine light for no IGF from the ignitor but that doesn't always seem to happen can only guess that odb1 is just inconsistent. a low idle is a symptom of this problem along with the running rich, cat glowing or overly rich smell.
The 1uz is pretty bulletproof up to any mileage with regular maintanence, but coilpacks are like its Achilles heal but they last at least 150k which is really not that bad.

 

I just picked the car up from my buddys shop and it runs better than it has in the past five years. He pulled the gas tank and said it had a ton of sludge, replaced the filter which was nasty, new spark plugs he said they looked liked they had never been replaced, and all new plugs and some of the old ones were the wrong plugs, new serpintine belt, oil changed and tranny flush.

Now to start on all of the other things wrong with it.