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tsb891407tpsscrews.jpg | Hits: 10976 | Posted on: 7/31/09 | View original size (302.04 KB)

TSB 89-14-07 TPS Screws
Publication Date: JULY 14, 1989

FORD: 1983-89 CROWN VICTORIA, MUSTANG, TEMPO, THUNDERBIRD
1984-89 ESCORT
1986-89 TAURUS
LINCOLN-MERCURY: 1983-89 CONTINENTAL, COUGAR, GRAND MARQUIS, MARK VII, TOPAZ, TOWN CAR
1984-87 LYNX
MERKUR: 1985-89 ALL MERKUR LINES
LIGHT TRUCK: 1983-89 ALL LIGHT TRUCK LINES

ISSUE: All Throttle Position Sensor (TPS) mounting screws have a "Pozidrive" head. The "Pozidrive" head looks a lot like a Phillips screw head. Use of a Phillips head screwdriver to remove a "Pozidrive" screw will normally result in a rounded or damaged screw head. Many technicians think it is an overtorqued or "frozen" screw. An adhesive was also used as a thread sealant starting with the 1988 model year. This adhesive requires still more effort to loosen and remove the screw.

ACTION: To prevent rounded or damaged screw heads when servicing the TPS mounting screws, technicians should always use a #2 "Pozidrive" screwdriver.

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY

For the full procedure to reset the throttle stop screw, see this caption:


For other TSBs, check here.
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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 ratchet. 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 higher 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.

See also:
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