As per TSB PIP4578 (Fig. 4), when replacing the throttle body because of a P0121, perhaps in conjunction with a P0507, use an OEM-enhanced scan tool to relearn idle. If it doesn’t work, simply do a soft reset of the vehicle and reflash the PCM to the latest calibration ID. For whatever reason, if the codes and symptoms still do not disappear, the OEM recommends replacing the PCM and reflashing it.
2000 GMC Safari misfire
Using Mode 6, or a misfire counter on the Bosch Tech2 (Fig. 5), we can count cylinder misfires. Using OEM-enhanced bidirectional controls, a fuel injector power balance test can be done. The result of the test was that the misfire was related to the poppet-style fuel injectors and the issue was corrected by running a fuel injector-specific cleaner through the fuel rail (See Fig. 6).
It is recommended that if the misfires return to simply replace all the fuel injectors.
2009 VW Jetta 2.0L P2004, no symptoms
Volkswagens with direct fuel injection have major carbon build-up issues in their intake manifolds due to the high compression in the engine. It is recommended to either do periodic intake cleanings with a fuel system cleaner tool or consign the vehicle to having a symptom-less P2004 Intake Manifold Runner Stuck Open DTC. (See Fig. 7). If this DTC occurs, the intake manifold can no longer be cleaned. Instead, it will have to be replaced.
2000 Toyota Camry 2.2L running lean
Lastly, a vehicle that runs rich at idle, but not under load, typically has dripping fuel injectors. However, a speed density system, like a 2.2L Toyota, works the opposite way. All the systems on the vehicle checked out, but there was no way to verify whether the fuel injectors were responsible. Even though an HC per cylinder test with an emissions analyzer might find something, the only way to know for sure is to test the fuel injectors on a bench. Here, the Launch X-SonicClean does a sprayability test, which shows the injectors spraying at different levels and that the far left injector is dripping (See Fig. 8). The repair to this issue is to ultrasonically clean the fuel injectors.