Upgrading components on your Saturn Ion Redline, such as installing an LSJ throttle body, is a common path for enthusiasts looking to enhance performance. However, modifications can sometimes introduce unexpected issues. This article delves into a specific problem encountered after a throttle body upgrade on a Saturn Ion Redline: idle irregularities, particularly when the air conditioning is engaged.
After installing a new LSJ throttle body, initial tests revealed promising improvements. The idle became noticeably smoother compared to the factory throttle body. In fact, idling without the air conditioning running was described as “silky smooth,” with no occurrences of the P0507 code (Idle Air Control System RPM Higher Than Expected) or any engine stumbling.
However, engaging the air conditioning introduced a new set of challenges. While the system initially seemed to function correctly, after about a minute, the idle quality deteriorated, triggering the P0507 code once again. It’s important to note that the severity of the issue was reduced compared to the original setup. Instead of violent shaking, the engine experienced a more subtle “random misfire” sensation, suggesting the throttle body’s Idle Air Control (IAC) electronics were partially compensating.
Clearing the diagnostic trouble code and disengaging the air conditioning would return the car to its smooth idle state, only for the problem to reappear when the AC was reactivated.
Further investigation using a diagnostic scanner provided valuable clues. With the air conditioning off, Short Term Fuel Trims (STFTs) remained consistently in the negative range, between -5% and -7%. This indicates a slightly rich fuel mixture, which is often acceptable. However, with the air conditioning switched on, the STFTs shifted into positive territory, fluctuating significantly from +14% to as high as +32%. Positive STFT values suggest the engine’s computer is trying to compensate for a lean condition by adding more fuel.
The significant swing in STFTs when the AC is turned on points towards a potential vacuum leak or an issue with the Mass Air Flow (MAF) sensor or Volumetric Efficiency (VE) tables in the engine tune, especially under increased engine load from the AC compressor. While the user suspects the tune’s AC-related settings are stock, verification is needed. Furthermore, the current fuel situation, a blend of E85 and E10 93 resulting in approximately E30 fuel, adds another layer of complexity. The user is running a stoichiometric ratio of 12.97 for the E30 mix, which appears to be functioning adequately for normal driving.
To accurately diagnose and resolve the idle issue with the AC, it is crucial to eliminate fuel variability. The plan is to run the fuel tank near empty and refill with a known quantity of E85 at a different location before a scheduled dyno tuning session. This will ensure a consistent fuel baseline for accurate MAF and VE calibration.
In conclusion, while the LSJ throttle body upgrade improved idle quality in the Saturn Ion Redline under normal conditions, engaging the AC reveals an underlying issue causing lean conditions and idle instability. Further investigation, starting with verifying tune parameters and ensuring consistent fuel quality, is necessary to fully resolve the P0507 code and achieve a smooth idle with the air conditioning operational. A professional dyno tune after establishing a stable fuel baseline is recommended to optimize the engine’s performance and address these idle concerns effectively.
