97 Gtp P0171

[duke_winchester]

I just replaced the lower intake manifold gaskets (replaced with aluminum gaskets from ZZPerformance), supercharger gasket (garlock), injector o-rings, vacuum lines, etc. When I started the car up after doing all of this, it ran very eradically on idle, but smoothed out when I gave it gas. At this point (yesterday), there was no SES light. I checked vacuum lines and couldn't find any leaks. The weird thing is that if I turn on the A/C at idle, that smooths it out some.
This morning, the SES light came on. Had it scanned and it came back with P0171 System too lean. I started spraying some carb cleaner around and the engined revved when I sprayed at gasket between supercharger/intake manifold (just below throttle body), so I tightened up on the S/C bolts some more. That helped some. Idle smoothed out some, but I still detect some rough idle and the SES light is still on (even after I tried to reset it). Note: after revving the engine, the rpm drops down to just below a thousand for a few seconds, then drops down to between 500 and 750. Before I did all this work, the PCV valve, EGR valve, O2 sensor all seemed to work fine, and none were throwing codes. I also checked air intake and it is all clear.

Also, if i were to remove the supercharger again (S/C only, not the intake manifold), would I have to drain coolant in order to do so, and then would I have to change the oil again afterwards?

Any advice would be greatly appreciated.

[BNaylor]

Welcome to AF.

Unless you have doubt about your work I would try to rule out other possible causes maybe missed before removing the supercharger.

DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero the PCM is reducing the amount of fuel to compensate for a rich condition.

Here is the course of action per the GP GM service manual:

Check all vacuum hoses at intake system.
PCV Valve
Possible throttle body blockage (clean input screen and body)
IAC (idle air controller valve)
Check fuel injectors (bad o-ring seal)
MAF sensor
EGR valve
Check 02 sensor
Contaminated fuel