Fleetwood V8-368 6.0L VIN 9 FI (1982)
Idle/Throttle Speed Control Unit: All Technical Service Bulletins
ISC/TPS - System Operation
Bulletin No. T 84-11
File In Group 6C
Number
69
Date
Oct. '83
SUBJECT:
ISC-TPS ADJUSTMENT - DEFI AND DFI EQUIPPED CADILLACS
MODELS AFFECTED: 1980-1983 ELDORADO AND SEVILLE 1981-1983 DEVILLE AND FLEETWOOD BROUGHAM
Dealer comments and warranty claims indicate that a number of ISC-TPS adjustments are being performed on 1980-1983 Cadillacs equipped with
Digital Fuel Injection. This bulletin provides information concerning what symptoms can be caused by a misadjusted TPS or ISC, and some symptoms
that are not related to misadjustment but are often misdiagnosed. It also provides information on ISC-TPS system operation and proper adjustment
procedures.
I.
ISC-TPS SYSTEM OPERATION
The information provided below will assist in diagnosis of ISC and TPS misadjustments:
A.
TPS voltage is used to limit minimum and maximum ISC plunger travel. This keeps the throttle lever from touching the minimum air rate
screw at the low end, and from ratcheting at the high end.
B.
Below 10 MPH, idle RPM is controlled by the distributor reference signal within the TPS limits described above.
C.
The TPS voltage is used to set the throttle angle when:
a.
the vehicle is above 10 MPH with closed throttle switch, or
b.
whenever the engine is not running.
D.
Changes in the TPS voltage are used for acceleration enrichment similar to an accelerator pump on a carburetor.
E.
The TPS voltage is used for power enrichment. Since power enrichment occurs before wide-open throttle, the ECM will still command
power enrichment by the time wide-open throttle is reached, even if the TPS is misadjusted several degrees.
F.
Minimum air rate is used as a reference throttle angle to set TPS. The throttle position should never reach the minimum air rate setting
during normal operation.
II. SYMPTOMS LEADING TO UNNECESSARY ADJUSTMENT
Currently, many ISC-TPS adjustments are made because of symptoms that are not related to ISC-TPS misadjustment. Listed below are common
symptoms leading to unnecessary adjustment and the reasons why ISC-TPS misadjustment is not related.
A.
Rough, Surging or Erratic Idle:
Idle speed is controlled by RPM, not TPS, when the vehicle is not in motion. A misadjusted ISC could possibly cause constant high idle, but not
an unsteady idle.
B.
Poor Performance, Hesitation and Detonation (Pinging):
The TPS is used to set ISC position at speeds above 10 MPH during closed throttle. Acceleration enrichment is controlled by how quickly the TPS
voltage increases. Therefore, a misadjusted TPS will not affect performance. On 1981 DFI vehicles, however, hesitation may result from TPS
misadjustment due to the non-linear resistance curve of the 1981 TPS.
NOTICE:
1983 Service Information Manual page 6C-3, Hesitation Diagnosis, Step 7 and 1982 Service Information Manual page 6-3, step 9
should read "check for binding TPS", not "check TPS adjustment".
Diagnosis of these symptoms, which are unrelated to ISC-TPS adjustments, may be found in the 1983 Service Information Manual engine diagnosis
section, pages 6C-1 through 6C-4. This diagnosis is applicable to all 1980-1983 models (some components are not used on past model vehicles).
III. SYMPTOMS OF A MISADJUSTED ISC-TPS
Although symptoms caused by ISC-TPS misadjustment are infrequent, there are certain symptoms that indicate this condition:
A.
TPS Related
