I would like to compare some parameters with other members. I have a 2003 Monte Carlo with a 3.8L w/out supercharger. My desired idle seems a bit out of range, and my long term fuel trim seems a bit high. I did a lower intake manifold gasket replacement, but did not change out the upper plenum gasket.. However, I do not know what my readings were before I performed the work.. Also, all engine components are stock.. Thank you in advance..

Note: these parameters were taken at idle, in closed loop, with engine running at normal operating temperature.

Actual RPM: around 740
Desired RPM: 696
Short term fuel trim: fluctuates between -1 and +2
Long term fuel trim: +8
HO2S1: normal fluctuation
HO2S2: steady
IAC count: 28

 

Everything seems fairly normal, but your LTFT indicates that you may need a tune up - or maybe a vacuum leak or exhaust leak.

 

the slightly high idle and long term fuel trim values would make me think its a very slight vacuum leak somewhere. check all you vacuum hoses and throttle body gasket after the MAF and i'm sure you'll find something. if not the UIM gasket is probably leaking.