try using a sea foam engine cleaner available at most napa parts stores. disconnect your brake boost line from master cylinder and poor half a can down that tube. pouring the fluid is the key though don't stick the vacuum hose into the cleaner or you may get a vapour lock. the other half of the can poor into your crank case. after about 100km change the oil. do this a couple of times and it should solve your issue. mine worked on a 99rodeo! hope it helps