or vehicle fails emissions testing.
IDLE MIXTURE (TACHOMETER (LEAN DROP) PROCEDURE)
NOTE: On 4.2L engines, ensure idle speed and timing are set prior
to adjusting the idle mixture. If mixture adjustment time
exceeds 3 minutes, run engine at 2000 RPM in Neutral for one
minute, and resume adjustment. On 4.0L engines, idle mixture
adjustment is not possible.
4.2L
1) Remove carburetor and locate roll pins blocking idle
mixture screws. Drill through throttle body on closed end of roll pin
hole. Drive pins out with punch. Reinstall carburetor. Install
tachometer.
2) Operate engine to normal operating temperature, and adjust
curb idle speed. Place automatic transmission selector in Drive
(Neutral for manual transmissions). Turn mixture screws inward until
RPM drops. Turn screws outward until highest RPM is reached.
3) Turn mixture screws inward to obtain the correct decrease
in RPM. See LEAN DROP (RPM) table. Adjust both screws equally. When
mixture is correctly adjusted, replace roll pin to block adjustment
screws.
NOTE: If final RPM differs more than 30 RPM from specified curb
idle speed, reset curb idle, and repeat mixture adjustment.
LEAN DROP (RPM) TABLE
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Application Man. Trans. Auto. Trans.
4.2L .................... 50 ........................ 50
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THROTTLE POSITION SENSOR (TPS)
NOTE: Adjustment of TPS only applies to the 4.0L models. It may be
necessary to remove throttle body from intake manifold, to
access sensor wiring harness.
Checking & Adjusting - 4.0L (Automatic Transmission)
1) Locate the square TPS connector. Note connector terminal
identification stamped on the back of the connector. Turn ignition on.
2) Connect voltmeter through back of wiring harness
connector. Connect negative voltmeter lead to terminal "D" and
positive voltmeter lead to terminal "A" to check input voltage. DO NOT
disconnect TPS connector.
3) Hold throttle plate closed against idle stop and note
voltage. Input voltage should be approximately 5 volts. Disconnect
voltmeter positive lead and connect to terminal "B" to measure output
voltage.
4) With throttle plate closed, measure the output voltage.
The output voltage should be approximately 4.2 volts. If output
voltage is not within specification, loosen TPS retaining screws.
5) Partially tighten one retaining screw. Rotate TPS to
obtain correct output voltage. Tighten retaining screws once correct
voltage is obtained.
Checking & Adjusting - 4.0L (Manual Transmission)
1) Turn ignition on. Connect voltmeter through back of wiring
harness connector. Connect negative voltmeter lead to terminal
"B" and positive voltmeter lead to terminal "A". DO NOT disconnect TPS
connector.
