LexusTJT

Starts and runs normal for a minute or so then idle begins surging up/down after warm up.
Its a very low surging idle, barely runs down to about 300 rpm.
Have since thrown CEL codes p0171 p0130 p0133 p0150 p0153.

This all happened at once, not gradually over a period.
How should I begin troubleshooting this problem?

LoudonMan

Check for vac leaks. Common problem, as the hoses get hard over time, and you can't tell by looking only. Remove, look and feel. If they are hard, replace them. And/or but an big stogie, and blow smoke HARD into the vacuum booster hose. Engine not running, of course. Have somebody with good peepers look for you.

LexusTJT

The first thing I looked for was a vacuum leak but found nothing obvious.
I'll go back and re-check more thoroughly, including the smoke test.

I did replace the IACV with a remanufactured unit, no change of symptoms.
Also checked brake booster unit for vacuum leak by pulling & plugging the large vacuum hose, no change of symptoms.

LexusTJT

Problem Fixed.!.
LoudonMan's advice was spot on, found (2) vacuum leaks doing a smoke test.
One leak was large the other was small, both were hidden from obvious view.

SC400slide

iTrader: (11)

Awesome! Thanks for reporting back.