1996 Isuzu Trooper

Engine problem
1996 Isuzu Trooper 6 cyl Four Wheel Drive Automatic 150256 miles

After several attempts to try to pinpoint the issue with my Trooper, I have replaced the fuel filter, replaced the battery, replaced the cat. Converter, checked all lines they appear to be solid no leaking or excessive wear, ect. I still have issues with my car, now apparently worse than before. The car now has a pick up in the idle speed to 3500 RPM and if I shift it into any gear it continues down to normal. After this if I put this in park or N, it will continue to idle at the steady 3500 RPM. What would be the issue?
Ernest Brown
January 13, 2008.

Check out the related content below while we wait for the question to be answered by a professional mechanic.