Pull the freeze frame data to identify whether the leak occurred at idle or under a load. (Engine RPM PID and Load Pid, you could even use the vehicle speed as part of the reference) If it occurred at idle, then a vacuum leak could be at play, if it occurred under a load then a vacuum leak is NOT indicated as a cause. Once you identify under what operating conditions the failure occurred, driving the car though differing conditions (Idle, part throttle, cruise, heavy throttle) and watching how fuel trim is compensating under those different conditions will be an important piece of information. It's not beyond expectations that the problem could still be a random occurrence. If fuel trim isn't making a correction and there are no hard faults causing open loop, then the problem simply might not be there at the moment. Lastly using VE (volumetric efficiency) calculations against the MAF sensors reading helps to prove if the MAF air sensor isn't reporting the airflow correctly. You need to do a snapshot and capture engine RPM, MAF in grams/second, and ambient temperature all under wide open throttle and from there I could calculate the reported VE for you.

irish girl. You wrote "My main mechanic found nothing wrong with the car but said that the cat. converter was hot so it must be plugged and he sent me to the guy who welded my muffler to have it changed. They changed it but did not believe that that was the problem. That cost $110.00. It didn't help" First of all, a hot catalytic convertor is one that is working. If it's glowing RED HOT, then it's overworking because there is a problem in the engine allowing too much air, and unburned fuel into the exhaust. On top of that, find one good shop and tech and stick with him/her. Stop ping-ponging around. Your only compounding your own misery. You wrote" The other day the check engine light came on and I went to Auto Zone who told me it was the O2 sensor just before the convertor." Looks like you fell for the "free diagnosis" and you got what you paid for, an O2 sensor that cannot be proven you actually needed now. You wrote. "My mechanic changed that, changed the plugs and fixed my brakes and rotors for a grand total of $289.00 and my car is still wanting to stall or stalling." Don't lump in your brake work as part of the total you have spent to fix the stalling symptom. They have nothing to do with each other. Treat them as if the brakes were replaced on a different car. You wrote, and now we are concentrating on the stalling. " It stalls or tries to at lights, in drive-through's and now it stalls if I'm going along at a pretty good speed and stop. I told my main mechanic it was still bad and he said that he would clean the throttle body for me that that could be it." That is a plausible answer to the stalling, a good tech can prove if this service is required, and can perform it easily. It's also possible the symptom can be caused by something else affecting the air entering the engine at low RPM's, and the computers response to correct this is exactly the same as a dirty throttle body, and that is for the computer to command the IAC to open wider than normal. This would be a "cut a tree down to see the forest step" in some cases. Sort of once you find something that can cause a particular problem, you stop looking until you prove the problem still exists. You wrote" The mechanic who changed the converter hooked a machine up to my car drove it around with that thing hooked up to it. He said that all of the sensors are working and things are firing or whatever and he seems to think that the tune-up should have been taken further. He suggests that the boots and coils and that plastic thing that holds it all should be changed." Some more specific information would be invaluable here. I can guess what I think he is feeling in the car, and that is still a missfire. The Quad 4's are prone to having trouble with the coil cover and spark plug boots. If there is a problem there, the plugs should be changed again! The reason the plugs need changed again is the boots could be carbon tracked, and allowing the spark to leak right down along the outside of the spark plug, where the boot contacts it. This causes the new spark plug to also carbon track, and it will in turn result in a missfire, and damage the new boot starting the cycle all over again. "I'm running out of money. What is your opinion?" One shop, one tech for everything. Stop ping-ponging. Find someone that can not only diagnose and repair this, but will communicate exactly what they are going to do and why. The O2 sensor replacement is a clue IMO, to an air/fuel ratio issue. This can cause excessive spark demand under certian conditions, and contribute to the coil cover/ spark plug boot problem. There is no more expensive way to attempt to fix one of today's cars than to pull a code and throw a part at it. That's the limit of the ability of a parts store employee when it comes to diagnosing a check engine light. Just because you pull a lean exhaust "O2 sensor" code from the computer, that does not condem the O2 sensor. If you had showed up here with an O2 sensor in your hand telling me Auto Zone had diagnosed it, I would have sent you away. I definately would not have just installed it, because that is not enough proof to me that you really need it.

Your diagnostic system is trying to tell you that you have a misbehaving sensor. If is proven to truly be bad, what not replace it? When an oxygen sensor registers outside of the expected range, the system ignores it and sets a trouble code. Most systems substitutes a default value for the missing sensor and that value may not be correct for all conditions, but its good enough to keep the engine runnning and gets you home. You are probably running a little rich with the default code. You may have a heated sensor (electrically heated). The O2 sensors have to be very hot to work. If yours have 4 leads going to the sensor, it has a heater. Most sensors are not difficult to change provided you have the proper socket, one that accomodates the leads on the end of the sensor. O2 sensors are made in more than one size of hex nut. Be sure that you get the one that fits your model.

FWIW, I avoid aftermarket O2 sensors as much as possible. There is a clear difference in the O.E. part when it comes to accuracy and long term performance. That being said, when I see a part replaced and a code reset, my routine is to test the vehicle again from the beginning as if it has never been serviced the first time. This allows me to not assume that the part is either OK, nor defective. In otherwords, I test as if it's a completely different vehicle, and that routine allows me to solve problems that other techs/shops get stuck on. Cowboy is correct that even a lot of techs get stuck in the pull a code, change a part trap. The funny thing is, they get that way because it's what the public wants. While I have a diagnostic fee to just get started, they may attempt to give into public price pressure and try and do the diagnostics for a vary small fee, or even FREE. Well this is just like anything else, you get what you pay for, sometimes even less. Overall the worst thing that happens is after the owner spends a ton of money whether by their own hand, or with someone elses help and they have been unsuccessful with a repair, then they show up at a shop like mine crying how they already spent all that money and the car is still broke, almost as if it's my fault and now I'm supposed to make it right without earning a living doing so. Quite frankly when it happens too many times I am not afraid to send the customer permanently out the door. The most recent was a person that owns an Infinity Q45. They fooled around several times over the last few years, and each time I bailed them out. This last time they came to me first, I did the diagnostics only to see them take the repair to another shop for $5.00 less than I was going to charge! Heck they spent that $5.00 in gas just getting to that other shop and back home. Well they are free to make that choice, and now they can live with it, because between me, and the dealer, no-one else has full software support for their car, and it will never come back in here. My Choice......