Volkswagen Repair: engine problem on a 1987 vw jetta, vw jetta, gas milage


Question
i have a problem with my 1987 vw jetta(the german
version).the idle keeps fluctuating from about 500rpm to
1500rpm when at an idle position. i also seem to have lost
a bunch of power going up hills which i had before.i do
have 142,000 miles on it now by the way. my gas milage
has gone from 35mpg to between 15 and 20 mpg. i had it
to
my mechanic to see what they could come up with and they
thought they had it solved when they replaced the coolant
sensor unit but it started doing the same thing shortly
after. they kept it  for another day thinking they would
check
for vaccum leaks but could not find any. what are we
missing?
could there be something in some relays or other sensors
that are throwing this out of wack? oh, also the oxegen
sensor was replaced, the air filter, and the carb flappers
were cleaned. otherwise the car starts up instantly
when turning the engine. could you possibly have a
solution
to my pickle? considering the age of the car and the milage
on it, would you feel it is worth it to repair it? thank you
very
much for your time and patience. howard

Answer
vacuum leak.  Thats it thats all.  Check hose connections that they are tight, not loose fitting, that the hose ends are not cracked,  that the clamps around intake areas are tight.  I use brake cleaner in a spray(basically alcohol) and I spray around while the car is idling.  When the engine changes RPM or dies when I spray a certain area, that is where I focus.  You are sucking air.  You can do this check yourself.  Solution to your pickle...get a better mechanic  Hopefully they did not charge you for the unnecessary parts.
You got 142000 so ... I got over 720,000 mi and am not burning blue or anything and my car is 25 years old.  You might want to check the plugs and wires too