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scionking, Toyota Expert
Category: Toyota
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Toyota VX100 2003 seemed to have a TPS problem with the

Customer Question

Toyota VX100 2003 seemed to have a TPS problem with the engine stumbling at low revs, particularly at take off and more pronounced during cold periods. Problem was generally also somewhat intermittent.
Contracted with a mechanic (well experienced but not a Toyota mechanic) to check both TPS and Air flow sensor. New air flow sensor was fitted without improvement. TPS was removed and cleaned but the problem now SIGNIFICANTLY worse. The vehicle now does not recognise any movement on the throttle for the first 10 to 20 degrees rotation, and thereafter displays pronounced bogging and stumbling. Suggested calibration procedures from various internet platforms have been attempted with no success. Any suggestions ??
Submitted: 1 year ago.
Category: Toyota
Expert:  scionking replied 1 year ago.

Is this 4.7 engine?

Also was there a check engine light associated with this condition, if so do you have the ability to connect with computer and retrieve code numbers?

Customer: replied 1 year ago.
Thanks for your response.This is the 4,7 liter engine. There was no engine light associated with the problem and diagnostic plug in test revealed no error code at all.
Customer: replied 1 year ago.
The problem was definitely significantly worse once the TPS had been removed, cleaned and replaced suggesting that this might well be where the fault lies. My mechanic questions whether there is some form of gear mechanism within the throttle body assembly which may have worn or jumped a few teeth in the disassembling and cleaning ?
Expert:  scionking replied 1 year ago.

When replacing/installing the TPS, you have to make sure that the tangs on the end of the two arms on the throttle assembly are engaged with the slots on the backside of the sensor unit. To do this, make sure the throttle plate is closed, then install it at about 15 degrees to the right of its actual installed position, rotate it counter-clockwise until it touches the throttle shaft. Then install the two mounting screws lightly, i.e just tight enough to hold the sensor in position.

You'll then need a scan tool that tells you throttle position percentage. Turn the the ignition switch to ON. While reading the throttle valve opening % on the scan tool, turn the TPS slowly back and forth until you reach the standard range (between 14.6 and 16%), then set the mounting screws tightly.

Expert:  scionking replied 1 year ago.

Also attached is diagnostics for throttle related codes, although you don't have any codes this information may be helpful in determining if TPS is operating correctly.

Expert:  scionking replied 1 year ago.

Hello, I see you haven't accepted my answer do you require more assistance? If not please accept my answer and rate the service provided.

Thank you for using Just Answer!!

Customer: replied 1 year ago.
Good morning<Thanks you for your advice this far which I have passed on to my mechanic. I have not had any further feedback from him at this time but would presume that some progress is being made.
One last question I have relates to the functionality of the TPS unit. Assuming that cleaning and appropriate re-installation is all that will be required to get the vehicle mobile again, what indications might there be to demonstrate actual failure of the unit ? Will this be evident in the diagnostic scan ?
Expert:  scionking replied 1 year ago.

If the TPS sensor "electrically fails" then the check engine light would come on and one or more of the codes in the sheet I attached previously would appear. Other then that the TPS can also be misaligned or voltage values out of range from actual position, This will not cause a code but will trick the vehicle into thinking that it is lets say at 25% throttle when in actuality it is at 45% throttle. This will cause issues because the vehicle is expecting a certain amount of air to pass through the throttle at 25% and therefore matches the amount of fuel needed, but if it thinks its at 25% but its actually at 45% it will cause incorrect air/fuel ratio.