Again you are right with the coils firing if they get electricity. Hot or cold spark, but they will fire. Just keep in mind that other things also affect electricity. Like a loose belt on the alternator. Or a ground cable missing from the engine to the body. I have also been working on junk cars for 45 years. Started at 10 years old with my Dad. I do mostly electronics work now. Just fixing electrical and computers. Again you are right with the coils firing if they get electricity. Hot or cold spark, but they will fire. Just keep in mind that other things also affect electricity. Like a loose belt on the alternator. Or a ground cable missing from the engine to the body. I have also been working on junk cars for 45 years. Started at 10 years old with my Dad. I do mostly electronics work now. Just fixing electrical and computers.

Very valid points Randy. It makes sense if you think about your diagnosis. So, I would have to expand on my earlier diagnosis -- remembering that it is tough to diagnose a car problem this way -- to say the you do you also have to make sure the air filter isn't the problem. Pulling the air filter is easy and checking it is just as easy. Look at the owner manual and see where the filter cover is located. The pop the cover and remove the filter. The filter element -- the fuzzy stuff -- should be clean. If it isn't, it's a good idea to replace it. It is also a good idea to look, as you note, at the vacuum lines. To check them, you will need a service manual to indicate where all of the lines are located and then pull them one by one. When you find the one that's hissing, you've found your problem. Checking the line, itself, requires you to pull the line off its mount point and plugging the end with your finger. If the line hisses it is pulling in air -- it could be cracked or frayed or, since it is rubber based, just worn with dry rot, depending on the climate. Replace the line with the correct part number from an auto parts store and you are on your way. You can use any mounting hardware that is on your car if it is clean. If it isn't then you will have to replace the mounting hardware as well. Finally, as Randy indicates, there might be a problem with the tension on your Corolla's driver belt. The tensioner may have slipped slightly, loosening the belt. Press the alternator drivebelt with your thumb. If it moves more than half-an-inch you will have to tighten it. You will have to loosen up the alternator and move it slightly to take any slack out of the line and then you will have to retighten it. If you obtain the service manual, you will find the exact procedure outlined. It is easy but watch your fingers as the nuts freeze easily and they are a bear to loosen. Be sure you do not strip the head or the nut itself. If you do you will cause yourself endless headaches as you will have to then drill out the nut and tap and die the remaining hole to accept a new hold-down nut. It's a time-consuming process. Watch out that you don't jam your fingers, either (as happened to me once -- no stitches, but lots of red stuff). Very valid points Randy. It makes sense if you think about your diagnosis. So, I would have to expand on my earlier diagnosis -- remembering that it is tough to diagnose a car problem this way -- to say the you do you also have to make sure the air filter isn't the problem. Pulling the air filter is easy and checking it is just as easy. Look at the owner manual and see where the filter cover is located. The pop the cover and remove the filter. The filter element -- the fuzzy stuff -- should be clean. If it isn't, it's a good idea to replace it. It is also a good idea to look, as you note, at the vacuum lines. To check them, you will need a service manual to indicate where all of the lines are located and then pull them one by one. When you find the one that's hissing, you've found your problem. Checking the line, itself, requires you to pull the line off its mount point and plugging the end with your finger. If the line hisses it is pulling in air -- it could be cracked or frayed or, since it is rubber based, just worn with dry rot, depending on the climate. Replace the line with the correct part number from an auto parts store and you are on your way. You can use any mounting hardware that is on your car if it is clean. If it isn't then you will have to replace the mounting hardware as well. Finally, as Randy indicates, there might be a problem with the tension on your Corolla's driver belt. The tensioner may have slipped slightly, loosening the belt. Press the alternator drivebelt with your thumb. If it moves more than half-an-inch you will have to tighten it. You will have to loosen up the alternator and move it slightly to take any slack out of the line and then you will have to retighten it. If you obtain the service manual, you will find the exact procedure outlined. It is easy but watch your fingers as the nuts freeze easily and they are a bear to loosen. Be sure you do not strip the head or the nut itself. If you do you will cause yourself endless headaches as you will have to then drill out the nut and tap and die the remaining hole to accept a new hold-down nut. It's a time-consuming process. Watch out that you don't jam your fingers, either (as happened to me once -- no stitches, but lots of red stuff).

If the ground -- there is no alt as this is not a three-phase system -- becomes intermittent, then you will find the Corolla will perform when the connection became good and would fail entirely when the connection went short. If a wire goes short, the electricity flows at all as you need two sides of a circuit to make it conductive so electricity will pass. If the ground wire is disconnected entirely then the engine will not fire at all. If the ground wire or connector becomes worn or corroded, it will continue to conduct electricity until the wire either fails or becomes corroded and the electrical pulse is blocked. Because the electrical system is either on or off -- there are no in-between states -- I doubt very much if it is the ground wire or connector for the foregoing reasons. If the ground -- there is no alt as this is not a three-phase system -- becomes intermittent, then you will find the Corolla will perform when the connection became good and would fail entirely when the connection went short. If a wire goes short, the electricity flows at all as you need two sides of a circuit to make it conductive so electricity will pass. If the ground wire is disconnected entirely then the engine will not fire at all. If the ground wire or connector becomes worn or corroded, it will continue to conduct electricity until the wire either fails or becomes corroded and the electrical pulse is blocked. Because the electrical system is either on or off -- there are no in-between states -- I doubt very much if it is the ground wire or connector for the foregoing reasons.

You have a point there Marc. I would also look at when the last time it was tuned up. Plus having the fuel and air filters changed. I would so far as to do an compression test on it, As bad valves could cause this also. Or bad rings. You have a point there Marc. I would also look at when the last time it was tuned up. Plus having the fuel and air filters changed. I would so far as to do an compression test on it, As bad valves could cause this also. Or bad rings.

Randy, you bring up a couple of excellent alternatives. They deserve a look. Randy, you bring up a couple of excellent alternatives. They deserve a look.