My SC400 runs flawless and I love it. But it seems like more recently when I allow it to sit a few days it will on occasion start very roughly. I've heard a knocking once before and more recently smoke coming out of the exhaust. I am almost afraid to let it sit for any prolonged period of time now. The car runs great and has no other problems. Once you rev it up and let it run it is fine. Any help?

 

sounds like a toasted HG

 

How's the mileage? What oil viscosity are you running? I wouldn't worry about it in the slightest. The smoke is probably just hardened valve seals, so when the car sits for awhile, a bit of oil makes it into the cylinders. Mine knocks a little if it sits for a prolonged period too.

 

another possibility is something electrical such as a bad coil pack... mine used to do that, turns out there was a hairline crack in the coil pack on the drivers side, which let some moisture in if the car sat for a couple days - result was only running on 4 cylinders, which causes some smoke (unburnt fuel) and a very rough idle... as soon as it dries up, it goes away, usually only 15-30 seconds...

just a theory... might not be anything to worry with...

 

i also have a sc400 if it sat it did the same thing. it was valve stem seals and it was also compression down it number 7 cylinder. thats why when it warms it wont do it because the rings expand and so do the valve stem seals they soften up. its going to be expensive if you do want it fixed unless you can do it yourself. as for the knocking not good at all mine has 250000 and it doesnt do that i change my oil every 2500 with synthetic and lucas oil stabilizer which prevents dry starts the number one cause of engine damage. i deliver pizzas so i have to change it that often. what happens when you cut off your car all the oil goes to the pan and when you start it up the oil pump pumps it up to the top that causes drystarts. what lucas does is since its like jelly it always keeps the valves heads crank bearings connecting rods and pistons and walls constantly lubricated worth 15 dollars an oil change to completely eliminate dry starts in my opinion.

 

I change my oil every 5000 miles with right now 5W-30 here in Florida. The car only has 80k on it so it is barely broken in still. I might have to take it a shop and have A. Compression checked cold B. Check for a leak that would let moisture in

 

mine does the same when it sits over night, when i start it the next morning it runs very rich, white smoke comes out and runs rough... then after maybe 30 minutes of driving i shut the car off and let it sit for a while then when i start it up again, everything becomes normal, runs smooth as silk.. i know i have a bad ECU, i could buy a used one but im saving for an aftermarket one..