Trouble Codes 3, 13 and 14 for '93 Toyota Corolla

A few months ago I took my car in for brake work and a major tune up. 5 minutes out of the parking lot my check engine light comes on. I turn around, the mechanic reads the code and tells me it was an air intake sensor and that was probably bumped during repair. The light comes on again on the way home and I call the mechanic and he tells me to bring it back in later that week. That night when I am driving the Check Engine light comes back on but this time the car lurches and then corrects itself. My car continued doing this and I brought it back to the mechanic. Long story short, I have brought my car a total of 4 times to this mechanic and the codes now always read 3, 13 and 14. I have been told that these are ignition and knock codes and the mechanic is at a loss as to why this is happening or what to do. My car continues to lurch and correct and at times it feels like it is actually going to stall out. Can anyone offer me advice backed up with a bottom line estimate? It's a '93 and while it still runs well I can't keep dumping money into it. Also, any idea how much harm I am doing by continuing to drive my car in this condition or how long I can continue to get away with it? THANKS!