Volvo 240 DL 1990. When I driving up a fairly steep hill, which puts the engine under more than usual strain, smoke pores out the tail pipe. It's grey white and smells more like stinky exhaust, not like the plastic smell of burning oil. One other thing to note, the constant idle value seems to be stuck, so the idle is high, and fuel consumption is also high. Lastly there's a bit of an oil leak. The other day my mechanic replaced the O2 sensor. The idle seemed to dropped for a bit but now it's back up. One theory is, the engine is running to rich and when the car hits a hill gas pours into the engine which over loads the cylinders and causes excessive engine noise and smoke out the pipe. Of course at this angle oil could be pouring onto the exhaust manifold and smoking.

If anyone has an ideas would be great.