RPM's hanging up
11-28-2008, 09:46 AM
#1
Thread Starter
Join Date: Sep 2008
Location: Ky
Posts: 8
RPM's hanging up
I bought an 03 gt 5spd a few months ago. Every since I have owned it the RPM's have hung up between shifts. Sometimes it even gains RPM's when I push the clutch in. Also when I stop it will idle around 12 or 1300 for a few seconds then drop down a few hundred.
Is there a sensor that is bad or do they all do this? My last vehicle was a dakota and it was doing the same thing. It eventually got to where it would jup up to around 3 or 4 thousand when pushing in the clutch. It ended up being a sensor that was fixed for free due to a recall.
Is there a sensor that is bad or do they all do this? My last vehicle was a dakota and it was doing the same thing. It eventually got to where it would jup up to around 3 or 4 thousand when pushing in the clutch. It ended up being a sensor that was fixed for free due to a recall.
11-28-2008, 11:23 AM
#2
Join Date: Feb 2006
Location: Nashville, TN
Posts: 41
Hanging rpm's
The modulars from '99-04 are famous for this problem. I to have an '03 and had the same problem. You can either try and adjust your TPS for which youll need an OLM meter or you can go to the "how to" section and I think ther is a Blog that shows you how to drill a hole in the intake to help with the problem. If its not there look around in here, there are instructions somewhere. good luck.
P>S> I just adjusted the TPS myself.
P>S> I just adjusted the TPS myself.
11-28-2008, 11:25 AM
#4
5th Gear Member
Join Date: Mar 2006
Location: Dallas
Posts: 2,530
11-29-2008, 01:31 AM
#6
2nd Gear Member
Join Date: Jul 2008
Location: Florida
Posts: 243
I had this problem show up lastweek. Just go to advanced or Autozone and get a new Throttle Position Sensor (TPS) you can pick them up for around 30bucks. took me about 2minutes to do the install, all normal again.
11-29-2008, 08:31 AM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
The modulars from '99-04 are famous for this problem. I to have an '03 and had the same problem. You can either try and adjust your TPS for which youll need an OLM meter or you can go to the "how to" section and I think ther is a Blog that shows you how to drill a hole in the intake to help with the problem. If its not there look around in here, there are instructions somewhere. good luck.
P>S> I just adjusted the TPS myself.
P>S> I just adjusted the TPS myself.
Since the voltage applied to the TPS, and it's angular change in resistance, are both fixed values it is easy to calculate the % of throttle opening.
From the '03 shop manual:
Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start.
This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts.
In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.
All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID.
With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle.
Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start.
This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts.
In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.
All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID.
With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle.
Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.
As to the OP's original question, it is normal (and annoying) for the rpm's to hang between shifts, and for rpm to stay high until the car actually stops moving. The between shifts part is emissions related, the idle behaviour is related to the hydroboost braking system--it keeps the ilde high to make 100% sure there is sufficient power steering system pressure for the power assisted brakes.
Both of these can be modified with the various IAC mods that place a restriction in the IAC supply tube, or with the gasket type mod. They can also be tuned out with a low level (higher priced) tuner like Sniper's Commando system.
It is not not normal for the revs to climb noticably between shifts, and the usual high idle before stopping is 1100 to 1150 rpm.
His observation may indeed indicate a sluggish IAC valve.
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