Jim Grant's Tech Tips
'90 Geo Tracker, Surging Problems
Q:
I have a ‘90 Geo Tracker. The car surges when running. In other words
when you are driving with your foot on the gas pedal in the same position
the car will rev up and down. I have no idea why this is happening. Initially
I thought it was the fuel filter and changed it. That did not solve the
problem. Is it possible that there is a vacuum problem or something that
I am missing?
A:
I had an Oldsmobile show up at the shop that if you held the throttle
steady at highway speed is would slow down and then speed up every 16
seconds like a clock. What was the cause? It turned out that the oxygen
sensor for the computer was lazy (slow in responding). The lazy sensor
would cause the vehicle’s computer to slowly change the fuel delivery
from too much to too little about every 16 seconds. The vehicle would
speed up and then just start slowing down. The cycle would just continue
if you held the gas pedal steady. The strange thing was the lazy sensor
would test great with all diagnostic procedures in the shop bay. It wasn’t
till you were driving on the highway that the problem would occur. I’d
be looking at the oxygen sensor as a possible cause.
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