I bought a pair of shoes that hurt my feet, so now I don't buy new shoes. Got a tough steak from the restaurant so now I don't eat steak. Had a hard-to-diagnose problem with my car a few years ago, which is WAY too common with all the current inappropriate use of technology, so now I just ignore it when the Engine Computer detects a problem and tries to tell me about it.
See the lack of logic? The first glaring problem is with the fault code. Is that one code or four codes? If that is one code from an inexpensive code reader, that isn't terribly helpful. Beginning with '96 models those codes get a lot more specific and descriptive, but in the case of the injector, they never say to replace parts. They only indicate the circuit or system that needs further diagnosis. "Ignition system fault" is useless. There are dozens of codes related to the ignition system that get much more detailed.
The second problem with ignoring the problem is the Engine Computer is constantly running self-tests on many circuits, and it compares things to each other. As an example, it knows that when the engine has been off for at least six hours, the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature. When there is a fault code set for either of them, no code will be set for the other one if it develops a problem because the computer doesn't have a known-good reference to compare it to. Many years ago mechanics only had a few things to check when there was a running problem, and those checks took just a couple of minutes. With all the electronics on today's cars, testing each system and circuit could take days. Fault codes are instrumental in getting the mechanic to the right circuit very quickly. If a second running problem develops on your car and no code is set related to it, the mechanic has to first repair what is known, then putter around until a new code sets so he can diagnose that one. You may not even know when that second problem develops.
In the case of the large leak, that affects emissions and is why the Check Engine light must turn on, but it won't adversely affect engine performance. Now suppose a sensor problem develops that results in excessive fuel being dumped into the engine. You may not be aware of it because the Check Engine light is already on. If you keep driving it that way, the catalytic converter will likely overheat and melt. Once it plugs up, you'll have a very expensive repair that will wipe out any money you might think you saved.
The first thing you need to do is get much more detailed descriptions of any fault codes that are currently set. A large leak can often be found with a visual inspection. I don't know where to begin with the other things you mentioned. Those descriptions are basically saying there's something wrong with the entire system. There's only four major systems but well over 1000 fault codes related to them. The Engine Computer has already done for you what it could take the mechanic hours or days to figure out, then he has to diagnose what he determined to be the system with the problem.
Saturday, January 26th, 2013 AT 5:36 PM