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transman
transman, automotive instructor
Category: Car
Satisfied Customers: 4078
Experience:  28 years exp,complete autmotive diagnostics and repair
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1999 Isuzu Rodeo: 2WD..intermittent..TPS sensor..code and surging came

Customer Question

I have a 1999 Isuzu Rodeo 2WD 3.2L showing code P0122 with intermittent surging. I replaced the TPS sensor and cleared the codes. As soon as I turned the ignition on code and surging came back. The surging goes away after a few minutes and it seems to run fine. The wiring to the TPS looks ok as far as I can see. Waht else can I do or should I be checking?
Submitted: 5 years ago.
Category: Car
Expert:  transman replied 5 years ago.

transman :

hi,welcome to J.A. do you have a multimeter?

transman :

here is the circuit on that sensor you will need it to do the test

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transman :

here is information on
















Circuit Description
The throttle position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. The signal voltage will vary from below 0.6 volts at closed throttle to about 4.5 volts at wide open throttle (WOT). The TP signal is used by the powertrain control module (PCM) for fuel control and many of the PCM-controlled outputs.

Conditions for Setting the DTC



  • The ignition is ON .

  • TP sensor signal voltage is less than 0.22 volt for a total of 0.78 second over a 1.5-second period.


Action Taken When the DTC Sets



  • The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.

  • The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.

  • The PCM will use a default throttle position based on mass air flow and RPM.


Conditions for Clearing the MIL/DTC



  • The PCM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

  • A history DTC P0122 will clear after 40 consecutive warm-up cycles have occurred without a fault.

  • DTC P0122 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.


Diagnostic Aids
Check for the following conditions:



  • Poor connection at PCM - Inspect harness connectors for backed-out terminals improper mating broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.

  • The TP Sensor shares a 5 Volt reference with the EGR valve. If these codes are also set, it could indicate a problem with the 5 Volt reference circuit or components itself.

  • The TP Sensor shares a ground with the EGR Valve and the IAT Sensor

  • Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the throttle position display on the scan tool while moving connectors and wiring harnesses related to the TP sensor. A change in the display will indicate the location of the fault.


If DTC P0122 cannot be duplicated, the information included in the Failure Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1122 Diagnostic Chart may isolate the cause of the fault.




its function.

Customer :

Update: I rescanned and now also throwing code P0113 for IAT sensor, which I should mention was just replaced with the TPS sensor. Being that they sharea common ground wire is this where I should be looking? Does this sound like a wiring problem? I will investigate the wiring further in the morning but if anyone could could point me in the right direction or tell me what I should be looking for I'd appreciate it.

transman :

then the problem can be the ground. let me see if i can find the wiring on this sensors and get back to you.

Customer :

New update: I can now add code p1509 to the list after a short drive. PCM?

transman :

ok, let me look this up.

transman :

ok this is the idle air control valve , does the engine idles low or to hi?

Customer :

When started it idles low almost to the point of stalling. Depressing gas pedal produces surging however I've found that if I let it "warm up" ie idle for about ten minutes this goes away. I think from I've read that this is because the brain is sending a default signal to set the timing etc.

transman :

ok, have you done throttle plate cleaning? if the idle air control is carbonize it will cause this problem

Customer :

yes