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do you have any fault codes? Some codes if intermittent will store in the ecm but may not set the check engine light.
Sometimes a P1231 fault can cause an erratic idle speed.
also faulty Mass Air Flow sensor could be the cause. You really need someone with TECH2 and the ability to understand the data to diagnose it.
Here's the info on P1231
Throttle Position Sensor 1 and 2 Circuit. Sum Out of Range (No Limp Home).
Brief disturbances in throttle valve control that cause the engine to jerk.
Introductory information
· The DTC should be ignored if it appears along with other throttle body related DTCs.
Purpose
The purpose of this DTC is to notify that sporadic jerkiness has occurred at constant speeds and/or that idling is irregular. The jerkiness may be relatively uncommon and produce a sensation similar to driving over small holes in the road. In the worst cases the phenomenon may be similar to rapid, brief losses of engine power, which can lead one to believe that the ignition discharge module is faulty.
Note
The jerkiness must not be confused with the jerkiness that can occur at high engine loads.
Technical explanation
The phenomenon is due to faults in one of the potentiometers (pot.1) in the throttle body. The throttle will briefly move towards closed. This may give rise to an irregular idling speed or jerkiness during cruising. The disturbance is harmless from a safety point of view and does not affect exhaust emission control.
Diagnostic procedure
Ask the customer how often and for how long the symptom is experienced and how serious the problem is (does the throttle body need changing?).
On-Board Diagnostics
Type of diagnosis:
- Continuous.
Enable criteria:
- Engine speeds up to 4000 rpm.
- Constant accelerator position.
The number of jerks is registered and stored by the engine management system and ultimately generates the DTC.
Fault criteria:
- The engine management system has on repeated occasions registered that the throttle valve has not followed the request of the control module.
Dependents:
- None.
System reaction to a fault:
- None.
OK report:
- The DTC is erased if no jerkiness is detected for a long period of time.
Fault handling: (See section Fault handling III, other emission-related components and functions for more information.)
- Type III.
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