My car keeps stalling and idoling high

See thats the thing I did have a mechanic look at it and he told me the tps was cracked and needed to be replaced and I did that, I have been reading a lot about this car and it seems like this problem is going on with a lot of peoples buick lesabre very frustrating when you dont have the money to keep going to different shops Im thinking maybe the ECM?? because everytime a shop tries to hook up its computer to read the codes theres a connection error I dont understand?

If there is a connect error when connecting up a diagnostic tool, either they are inputting the wrong information, or car computer could be bad. Cars are made to run in a "Default mode" if something major goes bad, car will run, but not very well.

Although you have given some great information, and it is appreciated, the tensioner issue will have nothing to do with the ability to be able to read or not read the computer, and the alternator to be able to not charge and charge intermittently. Thanks for your input.