Idle low at 500 rpms. Where to look?

[777funk]

Also if I gun it and let off it kills.

[chrism]

I would clean out the throttle body if it hasn’t been done recently. The plate may sticking in the crud.
Are you getting any fault codes?

[vtl]

Look first at the fuel trims (STFT, LTFT). If it indicates unmetered air sucked in then smoke the intake next. No holes found - look at MAF. If the engine is turbo, IAT is also important. More important than MAF in fact.

[br0dy519]

Look first at the fuel trims (STFT, LTFT). If it indicates unmetered air sucked in then smoke the intake next. No holes found - look at MAF. If the engine is turbo, IAT is also important. More important than MAF in fact.

Is there any crash course for fuel trims? I hear about it often but I'm not sure how to interpret the data.

[vtl]

Look first at the fuel trims (STFT, LTFT). If it indicates unmetered air sucked in then smoke the intake next. No holes found - look at MAF. If the engine is turbo, IAT is also important. More important than MAF in fact.

Is there any crash course for fuel trims? I hear about it often but I'm not sure how to interpret the data.

Short term fuel trim (STFT) oscillates around 1.0 in a constant search for the better fuel utilization, you usually see it jumping from around 0.98 to 1.02. Some readers report it in centered around 0.0, others - in percents, like 98% to 102%.

When there's a problem with air or fuel, STFT starts to drift to lean or rich side permanently. At this point this deviation is committed into the long term fuel trim (LTFT), so that STFT can return back to 1.0. LTFT reaches some threshold, the code is thrown. In the worst scenario STFT is drifted far away from 1.0 and does not return back.

STFT larger than normal means computer adds more fuel than needed, which indicates a vacuum leak, i.e. intake has a hole. Or fuel is too oxygenated, like E85 is used instead of E10. Or fuel pressure is low in fuel rail.

STFT smaller than normal means computer reduces fuel delivery, which indicates problem like an injector leak or too much pressure in fuel rail.

Both can indicate problems with sensors, or ignition, or compression, too.

[vtl]

I forgot to mention both oxygen sensors are supposed to be replaced every 100k miles. Old upstream sensor will degrade engine efficiency (MPG drops), old downstream sensor will report the dead catalytic converter.