High HC at Idle???

[UZ4runner]

My 1uzfe out of a 93 LS400 failed emmissions at idle (590rpm). The max allowable Hydrocarbons is 220 PPM and 1098 was read. CO was measured a 0.54% (1.2% max allowable) The high speed (2500rpm) test passed at 173 PPM HC and 0.75%. Any Ideas what could be causing this?

Info:
1. I did find a loose spark plug after the failed test. There was obvious signs of leakage aroung the plug.
2. The EGR is blocked off.
3. I have been running 87 octane gas.

Any ideas? Thanks!

Andrew

 

[George_R]

High CH figures typically indicate incomplete combustion and maybe some oil in combustion chamber, the latter is likely due to never replaced stem seals.