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Discussion Starter · #1 ·
Have got a 02 4.8 dual fuel that idles at 1100 when warm in park ,can anyone tell me how to lower the idle without taking it to dealer Thanks

64 Posts
Straight From the Manual for a TB48 M/T but look the A/T is the same

Idle Air Volume Learning
“Idle Air Volume Learning” is an operation to learn the idle air volume
that keeps each engine within the specific range. It must be
performed under any of the following conditions:
I Each time IACV-AAC valve, throttle body or ECM is replaced.
I Idle speed or ignition timing is out of specification.
Before performing “Idle Air Volume Learning”, make sure that all of
the following conditions are satisfied.
Learning will be cancelled if any of the following conditions are
missed for even a moment.
I Battery voltage: More than 12.9V (At idle)
I Engine coolant temperature: 70 - 99°C (158 - 210°F)
I PNP switch: ON
I Electric load switch: OFF
(Air conditioner, heater fan, headlamp, rear window defogger)
I Cooling fan motor: Not operating
I Steering wheel: Neutral (Straight-ahead position)
I Vehicle speed: Stopped
I Transmission: Warmed-up
Drive vehicle for 10 minutes.

Engine and transmission Idle speed Ignition timing
type (in “P” or “N” position) (in “P” or “N” position)
TB48DE M/T 675±50 rpm 5±5° BTDC

1. Turn ignition switch “ON”. Wait at least 1 second.
2. Turn ignition switch “OFF”. Wait at least 10 seconds.
3. Start engine and warm it up to normal operating temperature.
4. Check that all items listed under the topic “PRE-CONDITIONING”
(previously mentioned) are in good order.
5. Turn ignition switch “OFF” and wait at least 10 seconds.
6. Start the engine and let it idle for at least 30 seconds.
7. Disconnect throttle position sensor harness connector (brown),
then reconnect it within 5 seconds.
8. Wait 20 seconds.
9. Make sure that idle speed is within specifications. If not, the
result will be incomplete. In this case, find the cause of the
problem by referring to the NOTE below.
10. Rev up the engine two or three times. Make sure that idle speed
and ignition timing are within specifications.
If idle air volume learning cannot be performed successfully,
proceed as follows:
1) Check that throttle valve is fully closed.
2) Check PCV valve operation.
3) Check that downstream of throttle valve is free from air
4) Adjust closed throttle position switch and reset memory.
(Refer to Basic Inspection, EC-93.)
5) When the above four items check out OK, engine component
parts and their installation condition are questionable.
Check and eliminate the cause of the problem.
It is useful to perform EC-121, “TROUBLE DIAGNOSIS —
6) If any of the following conditions occur after the engine
has started, eliminate the cause of the problem and perform
“Idle air volume learning” all over again:
I Engine stalls.
I Erroneous idle.
I Blown fuses related to the IACV-AAC valve system.

Premium Member
1,064 Posts
Does it idle too high on Gas only or on both. If it's gas only and you have a mixer setup there should be an idle screw on the converter. Mine is a 10mm bolt on one side.
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