I have a 1999 Chevy Tracker FWD 2.0 4AT. For several weeks my Tracker has been hard to start, and would occasionally stall for no particular reason. My Service Engine Light Soon light did not illuminate. I put my scanner on it and it turned up three codes, P0420, P0440, and P0455. The live data feed showed two issues:

1) Calculated Idle Air Control air flow was running at 63 gallons per minute (GPM). The standard is 0 to 43.99 GPM.

2) Fuel Tank Pressure 14mm Hg. The standard is -32 to 10 mm Hg.

I took the throttle body off, removed the Idle Air Control Valve (IACV), and discovered my breather hose was split. The breather hose runs from the top of the throttle body to the top of the valve cover. I replaced the hose (maybe that leak was why my IACV was reading high in the live data.) I cleaned the throttle body and the IACV then reassembled everything. I started the engine and the live data still showed too much airflow through the IACV.

I replaced the IACV with a new one, let the engine run so that the car's computer could figure out a new IACV was there, and the air flow was reduced to normal. I also observed that the IACV was now opening and closing in the live data.

Bottom line: Check out the live data on your IACV if you're experiencing similar symptoms.

I have not done any troubleshooting on the high fuel tank pressure yet. More to follow.

 

My Tracker started hesitating, stalling, bogging down, etc. The car was not setting any codes. I did see multiple codes but they were not permanently set. The Service Engine Soon light was not illuminated. I ordered a camshaft position sensor from NTK, installed it, and the car runs like a scalded jack rabbit.

Bottom line: Beware sensors made in China.