My sister has a 88 carolla sr5 coupe that deisels and the fourth and fith gears slip out cam any one tell me what would cause this

Switch to a higher grade of gas. Low grade gasoline leads to a greater degree of carbon buildup in the combustion chamber, which in turn causes the dieseling. In addition, to rid the carbon buildup try running Seafoam, or Ring Free or Quickleen additives. There's also "Carbon Guard," simply add it to the gas when you fill up. As to the slipping gears, it may need a little tranny tune up, check the fluid levels, and if it hasn't been serviced in a long while, change the fluid and filter. The bands may need a little adjustment, especially if it's got some miles on it.