Q

Venom_Nitrous said:

My car runs like ****! I tested my TPS voltage and when the throttle is closed, it reads 1.22 volts. When it is WOT it is at 5.40 volts. Isn't it supposed to be at like .98 at WOT. I am testing the middle wire of the 3. The top reads a full 12 volts and the bottem is a ground. The middle one is the one that changes when i open it. I just had it replaced. Could it be the wrong one. The car is the one in the sig. My car sounds like it has a monster cam in it when it idles low after first starting up like it is missing a cylinder. Then when I touch the gas, the RPM's hang at like 1700-3000 and won't go down unless I unplug the iac. What the hec is going on here. Maybe I can make a vid tomorrow.

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quote from the PC/ED book 2000 mustang said:

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.

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