Strange TPS? STRANGE NO MORE!!!
Mine - '03 Rubicon, 40,000 miles
Occasional sputtering, popping, backfiring, when accelerating.
Sometimes part throttle backfire.
If it was a carb I'd suspect accelerator pump or maybe a hunk of flotsam in the bowl.
As FI it's exhibiting typical TPS problems.
Throws code "TPS High" - verifies suspicion.
Code returns after clearing almost immediatly.
In fact, when driving it felt like the computer did not know I changed foot position, it would falter, then you could feel the MAP sensor compensate for the lower vacuum with more fuel. Then once it "caught" you could feel the feedback system working to get it right. It was interesting to play with like that.)
Voltage check: 5 volts reference - OK, ground - OK, 5 volts on the wiper throughout sweep range - no change! Bingo!
Disconnected - Ohmmeter check on TPS shows no change in resistance through out the range of movement. (Tried both Digital and Analog Ohmmeters.) Bingo - TPS gone south -- Right? Certainly not rocket science.
New one from the dealer - Ohmmeter check shows exactly the same thing! Wiper does not change in resistance.
Must be bad from the factory.
Swapped it for another out of the dealer's stock - we were going to send the first new one back as defective.
Resistance check shows the same - the wiper does not change in resistance! 2 bad new ones?
Now the real puzzlement - installed that one - voltage changes as it's supposed to -- but how? I must have done the resistance check wrong. Disconnected - tried the Ohmmeter again - does not show a resistance change! Reconnected, voltage sweeps as it should!
Drivability problem gone, runs fine again - but it makes no sense!???
The service manual shows the TPS as just a simple variable resistor. We found another one under a work bench at the dealer - but the older version - it sweeps with the Ohmmeter like expected.
All the other TPS's I've dealt with over the years have been simple resistors - potentiometers - and can easily be checked with an Ohmmeter. But this one stymies me!
I even tried using the Ohmmeter with opposite polarity - a difference in the Ohmmeter reading could indicate it's an active device rather than passive - semiconductors involved inside. No difference.
Sure, the symptoms and code indicated the TPS as being defective, but I'm a believer in verifying before throwing parts at it.
Why won't it show with the Ohmmeter?