# Can TPS cause transmission shifting issues?



## Joeyfoglepathfinder (Apr 6, 2018)

1999 Nissan Pathfinder se 4x4 

I recently replaced my Distributor cause of misfire and stalling issues. Before I replaced idle was maybe 0-300 rpms above regular idle. Some days it was fine. Some days it barely would idle higher. Nothing to serious. Once dist replaced, it was idleing at 1000-1500. After tweaking with throttle screw, and new idle air control valve a bit, and making sure I had timing set correct on new dist, I got idle in park neutral to get to about 900 rpms, and idle in drive and reverse stayed at about 1100-1400. I decided to tinker with my throttle position sensor which was recently replaced as well, but needed to be removed to make dist installation easier and was possiblly put back on wrongly calibrated causing higher idle. After messing with tps to lower idle, I got park neutral idle to stay at 750ish and sounding good. But soon as it’s put in drive or reverse, it idles at about 1100. Kinda annoying but nothing serious and not holding me back from doing its first test after dist replacemt. 

Long story short, after doing all that and letting car warm up plenty for maybe 30 minutes(50 degrees here, not too cold but just wanted to test for it’s stalling before taking it out) I go to back out the drive way. I put it in drive, go to accelerate down the street and immediately noticed I had poor acceleration and when it went to shift into a higher gear it would shift to early. It’d be in 4th gear before 25/30 mph. and wouldn’t down shift at higher rpm or slowing down. Once below 30 mph it would finally down shift into lower gears. Nothing like this before dist replacemt/tps adjusting. 

To ask. Could a poorly calibrated tps(mine bolts on with two bolts but can swivel and be adjusted before tightening) be the cause of these transmission issues. Never had skipping issuses at all even at full throttle. Still isn’t slipping just shifting to early and poor acceleration. Just wondering if Tps helps control shift points or could cause these symptoms. 

-Thanks in advanced, ya boy, Dirty P


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## rogoman (Dec 16, 2004)

The idle air control valve only affects the idle speed; it functions to maintain an idle speed of 700 rpm whether the car is in neutral, drive or A/C is on or off. If you're having problems at higher road speeds, the TPS is either not adjusted correctly, might be defective or the harness connector is insecure. Perform an ECU code readout to see if you're getting a code P0120 which is for the TPS. Here's a procedure taken from the FSM for your vehicle:


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## smj999smj (Jan 1, 2006)

"Tinkering" can cause more problems than it fixes. Before making adjustments, consult the factory service manual for the proper procedure. You can download the "engine control" chapter for free at NissanHelp.com from their "Knowledge Base" section or a complete manual at Nico Club's site. As shown in rogoman's post, the throttle screw should never be adjusted (unless someone already has and you need to reset it to the proper setting). The TPS adjustment is very specific and also requires relearning the closed throttle position. There were a couple of TSB's on this issue. One was for an updated TPS and adjustment procedure. The other was for a kit designed to limit throttle deposits which can cause problems; the kit is no longer available, but one could argue that it's not really needed if you clean your throttle body occasionally. Here are links to those bulletins:

NTB01-011:

https://x.nissanhelp.com/forums/local_links.php?s=&catid=449&filter=&sort=d&page=1&pp=10&keyid=32

NTB99-053b:

https://x.nissanhelp.com/forums/local_links.php?s=&catid=452&filter=&sort=d&page=1&pp=10&keyid=507

Idle and cold start fast idle are controlled by the IACV-AAC valve via the ECM. In order for it to function properly, the base idle setting needs to be properly adjusted. Base idle and ignition timing should be adjusted in ECM "timing set mode." This is accomplished with the engine fully warmed up and the TPS unplugged. Refer to the FSM for more info on proper timing and base idle adjustments. Also, make sure your coolant is reaching proper temperature; if you see your coolant gauge reading low, you likely have a stuck open thermostat which will cause issues, including the inability to properly set timing and idle.


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## Joeyfoglepathfinder (Apr 6, 2018)

To start thank you both for a comment and yalls input. Although my higher idle is annoying, it’s only when it’s in drive/reverse. In park/neutral it idles perfect at 750, no rpm jumping. But in drive it’ll idle and hold 1200 or so? The idle relearn techniques are very helpful as I still want to correct that issue. Between a new tps, O2 sensors, iac valve, a new dist, a maf cleaning, new plugs and wires, new fuel filter and a full throttle body and intake cleaning, I’m sure it had trouble finding the right idling speed, especially when I haven’t even put 20 miles on the car since all that to give it a chance to relearn. Those will help big time in setting that. 

But to ask, can a badly positioned tps cause the vehicle to accelerate poorly and to not shift/down shift correctly? It’s doesnt have as much power When accelerating, maybe half or 2/3 power. And it shifts to high to quick. It’ll go through first slower but reach higher rpms before going to second. But once in second it’ll shift to 3rd gear to soon. And once it shifts to 3rd, it just as quickly shifts higher into 4th gear giving 3rd no chance to raise car speed and rpms. 

Again, could a bad/ poorly positioned tps cause such poor acceleration and bad shifting points?


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## smj999smj (Jan 1, 2006)

Yes, the TPS can cause improper shifting if it is faulty or improperly adjusted, which is what occurred to prompt technical service bulletin NTB99-053b. Idle issues can occur if he closed throttle position is not relearned. 
On another topic, the idle is not "relearned" like it is in later Nissan vehicles; the VG engines were still kinda "ol' school." Driving it will not correct an improperly set base idle and as I mentioned earlier, the base idle has to be correctly adjusted using the proper procedure in order for the IACV-AAC valve to control the idle properly. So, if it were me working on the vehicle, I would first make sure the throttle drum set screw is properly adjusted; you may be able to look at the threads and see where it used to be positioned from the factory. Next, properly adjust the TPS as indicated in the TSB and then relearn the closed throttle position. Next, I would warm the engine up and make sure it's reaching normal operating temperature; if not, check or replace the thermostat. If it is, then shut the engine off and unplug the harness connector from the TPS. Start the engine and rev the engine a few times and let it idle. Adjust the base idle using the screw on the IACV-AAC valve to service manual specs and also check/adjust the ignition timing using a timing light. Turn the engine off and re-connect the TPS connector. Erase all stored trouble codes. Start the engine and road test and see what you have.


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## Joeyfoglepathfinder (Apr 6, 2018)

Thank you very much!! That was a very explanatory response. I had more questions as I was reading about setting proper idle and how to “relearn” closed throttle position. But as I read on you basically followed up on your previous statements. I’ll take off my tps and set that base idle with the iac valve screw like you mentioned. Do I do that with the it in park/neutral/drive? Or does it matter? Also when “learning” closes throttle position, does it have to be in a certain gear as well? 

Again thank you for your detailed response!


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## smj999smj (Jan 1, 2006)

Adjustments should be made in "PARK" or "NEUTRAL." The same goes for re-learning the closed throttle position. The TPS doesn't need to be taken off, just unplugged.


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