Yup- sensor is going out and the mechanic probably won't physically see the problem unless you leave out at their place over night and he (she) fires it up from a cold start. I had the same problem and I'll caution as to what happens next. Soon, on a cold start, you'll not be able to keep the RPM up high enough to prevent a stall. I had to drive home a few days ago with one foot on the brake & one on the gas to prevent stalling during slow downs & stops. Brought it to Isuzu mech and their computer discovered I had 3 different sensors that were failing. Replaced all 3 (althought only 1 really needed immed attention) & had oil changed..... for a discomforting $500.
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Blowjob maid