1990 cadillac seville leak repairs

it all depends on where the leak is coming from so $50 to $1500

Th engine have oil all around. Its dificult to tell whit out see it. But wash th engine in a car was. Then let it dry, start th car and u will see where is this leak starting from

This has nothing to do with the windows, probably just bad luck. Everything you need to know about the security system on your cadillac is on this link. Your system is called VATS.

http://vatspasslockpasskeysecurityhelp.yolasite.com/

could be a head gasket or intake gasket or thermostat gasket

I've got the exact same problem on my
Seville. It skips on #1 cylinder when first started. I just added BAR'S Leaks Liquid Copper to coolant, as I assume I've got a leaking head gasket. I'll let you know how this works out.

should be dexcool is it orange? if its not orange then any green will be fine but dont mix the 2 together. The best way to fix an oil leak is to find out where exactly it is coming from

Check tightness of your belts also check your water pump for a leak or damage.

When the problem is a vacuum leak you also have troubles at idle.
The vacuum can be tested using an hand tool gauge like this.
Vacuum/Fuel Pump Tester Kit
Once you find the leak, replace the leaking part.
Often it is easy to find the leak at a glance, as it is hissing or you notice the air out from the leak. Other techniques are pumping smoke inside vacuum or spreading soapy water on vacuum lines.
check also the EGR valve.
If you need the vacuum system diagram purchase a repair manual like this one : 2000 Cadillac SeVille STS Repair Manual on CDROM .
Here also a free tutorial on vacuum problems.
Regards.

oxygen sensors are fine you have a air leak check intake for leaks start with checking all inlet pipes rubber hoses if ok check fuel press if ok most likely mass air flow sensor i am leaning toward air leak.

It might be the fan relay switch. When the car gets warm check to see if the fan comes on.