Hello,
Wanted to share my experience with an engine issue that took a couple of weeks and about $400 to find.
I just bought my 1999 4X4 5-speed with 192000 one-owner miles. Day one driving from the dealership, I noticed a missing from the engine when the RPMs were between 1800-2300 or so. The issue would happen at other speeds, but not as often, and never under heavy acceleration -- only when the throttle was lightly applied.
Local mechanic kept it for a week. Checked codes, changed wires, plugs, boots, cleaned throttle body, checked injectors, etc. No luck. Those things needed to be done for sure -- the truck had no service history -- so, no tears shed. But the problem still there.
Frustrated, I bought a $30 bluetooth OBDii interface and bought the $5 Android app (Torque). Hooked everything up and added the MAF and throttle position widgets to the main screen so I could see if those sensors were bobbling around during the missing.
Sure enough, not 100 yards from the house, the engine skips and the throttle position graph drops from 15% to zero and then back up to 15%. Every skip showed up on that graph.
I then read the codes and there it was: P0120 - TPS. Well, why didn't the mechanic see that?
To make sure, I pulled the connector off the TPS and read for continuity and linearity between the two outside contacts with my ohmmeter. The thing was all over the place. Couldn't get a solid reading, and clear drop-out points along the range of motion.
Bought a replacement TPS at AutoZone ($55), swapped it out, and drove an hour. No more skips. OBDii TPS graph is smooth and flat when it is supposed to be with no jumping around.
Driving to San Antonio from Houston tomorrow for a bachelor weekend -- glad I figured it out