Moving beyond the K&N filter, I turned my attention to the throttle body. Although a throttle body cleaning provided temporary relief, the OBD2 P0121 code and associated symptoms returned quickly. Upon inspection, the throttle body didn’t appear excessively dirty, but I did observe a small buildup of carbon residue beneath the throttle plate. While cleaning offered a brief improvement, the problem resurfaced, suggesting a deeper issue than just surface carbon deposits.
Considering all the evidence, I’m now leaning towards a defective throttle body as the root cause of the P0121 code. The subtle oil residue, while present, doesn’t seem consistently related to the problem’s occurrence. Furthermore, the error code itself points directly to an “unexpected throttle position,” not a mass air flow (MAF) sensor or related issues.
Interestingly, the P0121 code only seems to trigger under specific driving conditions: when applying a slight throttle input while going uphill or downhill. Normal acceleration or more aggressive throttle inputs that cause the vehicle to downshift don’t seem to cause the problem. This pattern suggests to me that the throttle body might be sticking or hesitating momentarily, particularly with small changes in throttle position.
Has anyone had experience replacing a throttle body on a 2.4L engine to resolve a P0121 code? From what I can gather, it appears to be a straightforward, bolt-on replacement. Online parts retailers even list replacement throttle bodies for around $125. Is there any reason why attempting a throttle body replacement wouldn’t be a reasonable next step in diagnosing and fixing this OBD2 P0121 issue?
In the meantime, I’ve found a temporary workaround: using a more assertive throttle input when accelerating uphill. This seems to prevent the conditions that trigger the P0121 code, allowing me to drive without the error reoccurring, at least until I can address the suspected throttle body issue.
