E055

TEST CONDITIONS
1. No problems detected on the throttle position sensor or throttle switch circuits;
2. At key off the ECM will test for a misadjusted TPS (see Description).
3. Engine has been running for 10 minutes with coolant greater than 70°C.

FAILURE CONDITIONS
"Learned" TPS is less than -2.9° or greater than 3.0°.

ACTION TAKEN
At next key on, the ECM will log Code EO55 as current. No telltales are illuminated.

DESCRIPTION
The TPS on 1987 PFI engine is "self adjusting". At key off the ECM executes a TPS learning routine only if the engine had been run long enough to warm up the underhood environment. After key off, the ECM will retract the ISC until the ISC throttle switch opens and the throttle linkage is resting on the minimum air screw. At that time, the ECM stores the TPS value and calculates a correction. If the same correction factor occurs on two consecutive key "off" cycles, the TPS is then corrected to 0 degrees using the correction factor "learned". If the value needs correction by more than -2.9 degrees or +3.0 degrees, Code EO55 will be stored in memory at the next key "ON" cycle. Because the ECM tests for Code EO55 alter the engine has been running for a certain period of time, a current Code EO55 cannot be cleared using the ECM clear codes mode. Disconnect the negative battery cable for 10 seconds to clear a current Code EO55. Note: Parameter ED01, TPS, displays uncorrected TPS values.

Notes on Fault Tree
1. Checking TPS adjustment. ECM Data ED01, TPS displays uncorrected TPS so that it can be used to check TP5 adjustment.
2. TPS adjustment is OK.
3. If TPS adjustment is OK, ISC and throttle switch operation need to be thoroughly checked. The throttle linkage needs to be checked for proper operation -- throttle, cruise and TV cables not binding, proper throttle return spring operation throttle shalt and blades free to move.

Notes on Intermittents
Manipulate ISC wiring while observing ECM Input EI72 and while observing ISC operation during ECM output Cycling EO07.

Manipulate TPS wiring and connector while observing ECM Data ED01, TPS. Check for TPS secured to throttle body (both TORX screws tight). Cycle the TPS through its full travel while observing ED01 for erratic behavior. Check for
proper part number TPS installed on vehicle.

Remove and replace the TPS, ISC and ECM connectors and ensure that they are latched.