Hey all,

I have a 1988 saab 9000, manual trans, non turbo. I recently had my
knock sensor replaced, after driving on a bad one for many months (this
was causing my engine to run very badly after around 10 minutes of
driving). the day after getting my knock sensor replaced (as well as my
idle belt pulley, and some bad belts), i began to hear a very
click/tapping noise whenever the engine is at 2.5 rpm. The engine runs
great, and is unaffected performance wize by the sound. While
accelerating, the engine will click and tap once once hitting 2.5 rpm,
but stop once past. when the gas pedal is released, it will click as it
passes 2.5 rpm on the way down. during highway driving, if a speed is
held at 2.5 rpm, the engine will click and tap constantly.

I have noticed that after prolonged high speed driving, the engine
tap/click seems to all but disappear, but then returns the next day.
This also may be my imagination, but the click seems to be less on
rainy days.

i've been told that engine click can come insufficient oil on lifters,
dirty fuel injectors, engine knock, and bad air hoses (i don't know
much about that). most mechanics who have taken a listen to the noise
say its not lifters. I used fuel injector cleaner on this past tank of
gas, and while my engine seems to accelerate a bit smoother, the
clicking noise still lives. the mechanic who replaced my knock sensor
doesn;t think it is engine knock, but can't be positive.

If anyone has any ideas as to what this could possibly be, your help
would be greatly appreciated.