My 93 year old father has a 1989 Toyota Corolla which idles rough so he increased the idle speed but it idles too fast (20 mph at idle) The idle speed varies with a 10 second period from fast to slow almost dying at the low speed. I checked the carburetor for vacuum leak so the engine idles smoother when I put my hand over the carb throat. My dad will not let me take it to a shop to have it repaired so I am trying to fix it myself but his Hayes Repair Manual lists too many things to check. Anyone have any suggestions?

That's why they disabled the idle adjustment in later cars--people including me!) would just crank up the idle instead of getting to the root of the problem and giving the car a needed tuneup.

It probably just needs a tuneup (changing the spark plugs and spark plug wires.) The spark plugs are always in fire and literally burn up, then they can't explode the gas in the engine with as much power. Idling doesn't generate much power to start with, bad plugs reduce even that and Presto--not enough power to even keep the engine going by itself.

This needs to be done every 25,000-30,000 miles, or you will lose power, burn more gas, fail emissions tests, and have it die on you unexpectedly. If you can't remember when it was last done, I'd start there. And write it down and put it in the glove compartment, and write it on your calendar twice a year to check to make sure you don't forget it. but of course, you should be getting a 30,000-mile service at 30k-60k-90k miles that includes it...

My 87 Civic went 240,000 miles, dying only because I failed to change the timing belt, and whenever I thought it was dying it just needed a tuneup.

Best regards,
Mike