Toyota Repair: Burnt smell, pat lobb toyota, extended warranty

Question
I have a 2003 Corolla.  For about 3 months I have been smelling a burnt smell like plastic. I have taken it in once and had the struts replaced, once the heater core(I just knew that was the answer), but it started smelling again.  I have taken it to Pat Lobb Toyota and they have not found it - twice.  There is no plastic bag that I have picked up. I smell it more when the temp is high (I live in Texas)Not usually in the morning as it's been sitting all night. I have about decided it has something to do with the AC.  When I turn it off the smell stops,but of course it could be that the AC is bringing it in from the motor too.  My extended warranty expires in March and I am really trying to find out what the problem is.  My car is an automatic and the AC works well. I also have new tires. Please help !!  Thanks

Answer
The reason the smaeel goes away when not using the a/c is that air from the outside stops coming into the passenger compartment. There may be an oil leak, it may be small, just enough to drip on the exhaust once in a while, the heat from the exhaust burns the oil and it will not drip on the ground, it's a possibility. Have it checked for an oil leak.