Q: I have been working on a lexus ES350 I'm getting codes p0300 p0174 and c342d and can't figure out what the problem is, can u help?

C342d relates to faults in the throttle position sensor (TPS) or the idle air control valve (IAC). Check the wiring to the TPS sensor and the IAC valve and test for high resistances which will show up as voltage drops. P0355 can be caused by wiring faults but also by a faulty IAC valve so the IAC should be looked at closely. The TPS sensor response can be tested using a real time scan tool. With regard to the other codes, two common denominators across those codes are oxygen sensors and vacuum leaks. To resolve all of these codes, a real time scanner is necessary to look at actual engine operating parameters, for example the response of the oxygen sensors, the integrity of the heater circuit, and, with regard to vacuum leaks, to see if such leaks perhaps show up in measured fuel trims that are read off of a scanner. To have the required diagnostic steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, the recommended service to get your issue(s) resolved is a check engine light diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.