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Discussion Starter #1
I am currently experiencing issues with my 2001 ford mustang 3.8L v6 5-speed base model. I start my car lil rough idle for few seconds then levels out not uncommon for high mileage vehicles but I drive it for a while, doesn't always happen but extremely hard to drive when it does, ill be driving and I will press in my clutch to slow down to stop or change gears and whether I press my clutch in or move stick to neutral rpms will raise up to 2500 - 3000 and stick there till I put it back in gear and it will lunge when I do because of the amount of force produced. only time I can get it to stop is if I ease to a stop with it riding 2500 or more then right at a stop it sets for few seconds then slowly goes down. only way to stop it without being in gear. I have cleaned MAF, changed IAC twice second time to ford part, cleaned throttlebody, ran seafoam through it, checked throttle cable, tested neutral safety switch on clutch. need more ideas on what to check. ive heard bad TPS can cause it but figured it would throw a code or have issues at stopped idle.
 

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Check TPS with multimeter, easy.
Sometimes vacuum leaks increase idle.
 

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Discussion Starter #4
possibly tps

ya I checked the tps with computer, reading 0.94 like normal, no codes, but did key on engine running test and threw P0121 Throttle position sensor range code. Guessing it reads funky when not at constant idle. possibly causing the ecu to send readings to increase fuel and air mixture. tps is cheap to replace, ill get one today and set it to normal reading and see if problem continues. I will be back on to post results
 

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Guessing it reads funky when not at constant idle. possibly causing the ecu to send readings to increase fuel and air mixture.
The TPS is not used to change the AF mixture for the 96+ model years. It is used to compute closed throttle, part throttle, and WOT. On automatic transmission applications it has some effect on shift schedule.

The PCM re-learns the new closed throttle TPS value at each start up. Therefore it serves no purpose to "calibrate" the TPS value as was done on older Mustangs. The KEY to understanding the TPS is it must produce the SAME value each time the throttle is closed. See the write up on how to trouble shoot Idle/IAC issues.

Be aware of other "possible" causes for the reported symptoms.

Either the TPS reading is unstable because the throttle linkage is loose or worn.

Or the P0122 DTC is from the testing being done.

Or the PCM originally came from an automatic transmission application.

Or the TPS is bad. But this can be ruled out by working the throttle while monitoring the TPS value. Look for the value to be the same at closed throttle. Look for the value to increase smoothly as the throttle is opened/closed.

IMO your idle is sooooo high that you should start looking for vacuum leaks or excessive air passing through the TB butterfly. Even IF the TPS is bad, the idle should be in the 1100-1500 RPM range.

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P0121 - Throttle Position (TP) Circuit Performance Problem

The TP sensor circuit is monitored by the PCM for a non closed throttle position at idle. If key ON engine running self-test terminates upon placing the transmission range selector in gear (DRIVE or REVERSE) or when closing the throttle (idle) after opening it (in PARK or NEUTRAL) the TP closed throttle position is not attained, the test fails.

Binding throttle linkage
Damaged throttle body
TP circuit open to PCM
Damaged TP sensor
SIG RTN circuit open to TP sensor

Drive vehicle, bring to a stop, turn key OFF. Start vehicle, run key ON engine running self-test at idle. Access KOER diagnostic trouble codes on scan tool.
 

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Discussion Starter #6
Problem may be fixed

May have fixed the issue by replacing tps. old OE tps read 0.94, new OE part reads 0.98. no codes being thrown after replacement and drops back to idle with clutch pressed in and rough start has smoothed out, doesn't jump around as much. has not messed up several hours of driving after replacing today. If it comes back I will look for vacuum leaks. Thanks for everyones help with the issue.
 
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