[diamondjoe]

Thank god I came across this forum by chance. Sorry you had to find out the hard way. I took my 2000 Echo to the dealer because the check engine light was on too. Diagnosis was also the PO172, system too rich. I've been having trouble with fuel consumption and alot of bogging when I accelerate (no stalling yet...knock on wood). Toyota's said it need the mass air flow sensor replaced. I haven't done it yet (thankfully). I'll try your solution and see how it works. I've aready spent $108.25 just to have the diagnosis and find the code, and they wanted to charge me another $306.16 for the parts and labour on the MAF sensor.
Have you had any problems with your front bushings yet? My front end guy said Toyota is failing inspections left and right because of bushings being out. They said mine were both gone and needed to be replaced. He (front end guy) told me only one of mine was out a bit and the other was ok. He could rarely find anything wrong with the ones that had just been failed by Toyota. Furthermore, you can't get the bushings and you have to replace the whole control arm assemlbly. Toyota wanted me to replace both control arms for $988 plus another $68.94 for a highly recommended alignment after installation. What a rip off scam.
I'll let you know if your trick works for me, thanks again.