I have a 1999 Volvo S70 2.4L Naturally Aspirated with a brand new Fuel Filter, Fuel Pump, Fuel Pump Relay and many other little things. Replacing these made the car run perfectly for about two months after it had been sitting for about 3 years but a couple days ago it died at a red light and then started back up again but ever since then when breaking and sitting idle it will start to sputter out and the rpm will drop down to 0 and the kick back up to 1-2 and when it kicks back up black smoke will come out and when revving the engine black sludge came out. A day after that happened the ETS (Electronic Throttle System) light came on and continues to act up when idle like at a red light but runs perfectly fine when driving (like on the highway) any help / insight is very much appreciated. Thank you

 

Sounds like the electronic throttle module is going out. They are repairable....do a quick search