1994 SC400, Automatic.

I've been trawling through these forums for a week or more now since I got the car and I've tried numerous things to fix it. Here are the issues as they stand.

- Runs rich, I can smell fuel from the exhaust. No big white clouds though, just the normal seethrough vapour.
- Hesitating at idle, slightly rough, bumps up and down. Also doesn't need to warm up for some reason? Idle starts at around 600.
- Low power, maybe? I've only driven it around the block to test changes as I've done them, but it's slow to accelerate and just feels sluggish. Admittedly hasn't tested it since the last bout of installs.
- CEL and Trac Off come on, disappear after a few minutes of idling. I've checked the codes and they're 21, 27 and 29 - Driver-side Cat O2 sensor and the two rear o2 sensors. The rears I know about, the idiot PO cut them but I've done up some connectors and plugged them back in. They're Bosch OEM. Fronts I haven't checked but I have replacements coming.
- When I rev the car, it hits about 1-1100rpm and then the needle drops to zero. Car still revs. This didn't happen the first time I started it after installing the rotors, rpm needle was fine. Started again after fitting the engine covers/airbox. I've checked for vacuum leaks, it's shored up tighter than a bug's ****. Could be MAF? But the same thing happens with the MAF unplugged - do I need to reset the ECU after unplugging to test?

As a note, I checked the oil and coolant for milkiness or cloudyness and it's all fine, I don't think it's a blown head gasket.

So first thing is that I thought it was the ignition coils. If I unplug the driver-side coil, the car refuses the start. If I do the same to the passenger side coil, no issues. Replaced both coils, issue is still present, same thing.

Next I replaced the ignition wires and spark plugs, got some new ones in there, afterwards it seems to be running a lot better - the vapour from the exhaust is less thick and the smell isn't so bad.

Then I replaced the coils and rotors, the old ones were probably there from stock so they were all bunged up with carbon and crap. New ones don't seem to have made a bit of difference - ignition coil test still doesn't work.

I've checked the cat after 10~ minutes of idle, it's not glowing red or anything like that so I don't think it's blocked up. I did notice a little smoke coming from the passenger-side cat, or at least somewhere around it, what could that indicate?

I'm 99% sure I've wrenched it properly, the coils, wires, plugs and distributors are all installed correctly. It could be the ECU, perhaps? Or maybe the drivers side O2 sensor really is screwing things up? Honestly, I'm close to taking it to an autoshop and having them fix it. It'll cost more money, but it's been almost two weeks or me banging my head against the (admittedly gorgeous) engine block.

Any more ideas?

 

You've definitely been thorough in your troubleshooting. Replacing the ignition coils eliminated the last of my hesitation issues, but you've already ruled that out. (My coil test results were confusing, too.) I wouldn't think the O2 is causing the problems, since the CEL goes out once the car is warmed up. ECU is always a strong possibility when it comes to hair-pulling time. IAC and TPS could explain the hesitation, but not the other symptoms.

 

Took her out for a proper test drive today, came back home and the cats were glowing a beautiful cherry red. Could it be a bunged up cat causing backflow into the engine, and also killed the O2 sensors?

The real question is, is the original ignition problem that caused the bad cats still there and if I replace them is it just coming to come around again? It still smells a little like fuel from the exhaust, although mostly of burning.

Should I bite the bullet and take it all apart again to check my coils/wires/plugs before getting a new pair of cats?

Edit: As a side note, when she warms up the exhaust gets really super burbly, a much deeper tone. Is that blocked cats?

 

UPDATE

It was the coil. I replaced them both again, started up fine - When it doubt, check your coils.

Also, the cats were ruined, if you run it for any length of time on fewer cylinders than normal like the PO did on this one, get those replaced because they're going to be shot.

Car's been running beautiful for a couple of months now.