Check engine light ON with few black smoke

hi, recently bought a pre owned SC with the 1KZTE engine. Did not have any problems for the past few months but then a few days ago, I had the check engine light came up while I was on heavy traffic and the day was really hot. The engine power was also reduced and a little black smoke was coming out of the exhaust, also idling became poor. I suspect that the coolant temp sensor sent the check engine warning so I had the radiators flushed and the clutch fan refilled with silicon oil. Problem disappeared for a week but returned today again when the engine is running and the vehicle static with AC turned on. What should I lookout next? Observations are that the warning does not come out when vehicle continually moves thus passing air to cool the engine, there was a time that when the warning showed up the aux fan on the lower radiator is running even when the engine is off.

That fan is for the A/C.

Did you change the thermostat?

Does the main work as is should - you should hear it run on full speed during start up with the engine cover up of course!

No I did not change the thermostat as of now. I will change that and see if it will solve the problem. Thanks.

So the condenser fan suppose to run on full before engine start?

What else do i need to check?

No the clutch fan should whoosh on start up for second or two until the fluid is flung around the unit when it should drop to nothing and be able to be stopped with the engine running.
The condenser fan only with the A/C and therefore the engine running.

Fixed this already, it was a broken radiator cap.

Thanks for letting us know

How a small thing can cause major worries. Now i will be overhauling the radiator so that it will be more efficient.

Just make sure that the whole cooling system is free of any air pockets. Any time any Coolant is removed from the Cooling system you need to completely bleed the system including the rear heater. Make sure the rear heater tap and front heater taps are fully OPEN (Hot Position).
Get a small funnel to put in the Coolant filler neck at (Radiator Cap). Top up as normal. Run the engine until Normal Operating Temp is achieved. Keep topping the Funnel up about half way. As the Coolant flows through the system the gravity of the coolant from the funnel will eventually push out any trapped air in the system. This is important especially if a thermostat has to be replaced. Always check the operation of a New Thermostat prior to installing it. Dangling it into Boiling Water will see if it opens fully then closes when removed. I had plenty of occasions where a Brand New Thermostat was faulty or sticky out of the box. Once you're confident all the air has been bled from the system switch the engine off and let the coolant cool down as the coolant expands a lot when it gets hot. Top up if necessary then put the Radiator Cap back on. Make sure the Overflow Bottle is topped up to the correct level with Coolant. (Very Important). Run the engine for 15 - 20 Minutes and check Temp Guage is Normal. Air Pockets, even small ones, in the Cooling System play havoc with Sensors and can cause Overheating Problems. Also if you ever have to replace a Coolant Sensor, NEVER coat the thread with any kind of sealant. Use Plumbers Tape. If you get any sealant on the Sensor part it can affect it's effectiveness. Don't forget to use the Correct Type of Coolant and Correct Ratio of Coolant/Water.
Cheers

Thanks a lot mate for the tip!