It would greatly depend on the source of the leak, need more info.
depends on what is wrong with it you may need a new engine to fix it
This means that you have a gas leak somewhere in the engine compartment. The smell comes from the AC air inlet pumping in fresh air from the engine compartment, which is where the leak is. Check your injector o-rings for deterioration. Also check your fuel pressure regulator and lines.
Which heat shield? There are several.
there is no temperary fix ensure that the pcv valve is not clogged up or that the rubber connector is not broken. if the crankcase is under a vacuum it will go a long ways to reducing external leaks. i have been an auto mechanic for 26 years and i have countless seals replaced only to have the new seals leak as well it is imperative that you make sure it is not overfilled on the dipstick and that the pcv valve {positive crakcase ventilation} is functioning properly. there may be an accumalation of gunk in the hose, valve or fitting that restrict the vacuum from the intake mainfold. when there is excessive blowby from the piston rings it may require the fitment of a higher flow rate valve. if there is vacuum in the crankcase how can it leak oil out. only if presure is building up can it leak out. a rear seal is not a pressure seal it only stops the splash.
Every once in a while it will fix your evap leak if you replace the fuel cap, but usually the leak is somewhere else. A good repair facillity will have a smoke machine that can be used to fill the system with smoke and locate the leak by seeing where the smoke comes out.
Look for a vacuum leak.
First you have to locate the source of the vacuum leak, then determine the next step how to repair it.
I am having a stalling problem and I heard it can be the cause of a vacuum leak and if that is true how can i fix it and where is it at?
Need to know the location of the vacuum leak in order to answer this.
Depends on where the leak is located, and how much labor will go into fixing it.
It depends on where the leak is. If it's just a hose that is pretty easy to fix. If it is the manifold gasket that is a bit harder and can be expensive. Either way you need to get it taken care of soon because your car will not perform at it's best with a vacuum leak and gas mileage will probably be poor as well.
Fix it.
You have to determine the source of the leak then decide on how to fix it.
THAT SOUNDS LIKE A BAD VACUUM LEAK. IT SHOULDN'T COST MUCH TO FIX. IT MAY BE JUST A "HOSE" REPLACEMENT.
There are innumerable points for the leak, cost for repair will depend on where it is. You can drive the car only if the leak is minor and the temperature gauge shows normal temperature.
You cant
First you have to locate the source of the vacuum leak then you can determine what steps to take to stop the leak. Determine the source and re-post your question with more info.