My 95 convertible with 90k miles was idling rough and I was getting a code 32, 63, and 64, using my Auto X-Ray scaner. I took it to the local dealer and he replaced a vacuum valve (no other description on the invoice) and repaired some broken wires to the right O2 sensor. In one week, the rough idle was back. The dealer now says the car has a PO171 code, and wants 2k to do a tune up (plugs, wires, cap, fuel filter, and water pump). I guess I am old school, and think you should find the problem, before you start throwing parts at it. I have rebuilt many Vette engines, carburetors, and brake systems, but have no experience with C4 electronics. I need some direction for my trouble shooting. Since I am still getting the same 32, 63, and 64, plus the PO171, I assume I should be looking at reasons for the lean condition. Too much air or too little fuel. When the engine is idling rough, you can smell the raw fuel, and when I accelerate fast, I blow black smoke out the back. So I think the computer sees a lean condition on the right side, and dumps more fuel to both sides. The extra fuel is not completely burned, and is fouling the plugs. So I think I should start by replacing the fuel filter. Where is it located? The GM Service manual just says it is inline before the fuel injection unit, but does not show where. The next thing to look at is the right side O2 sensor. Check the wiring, and perhaps replace the sensor (why didn’t the dealer change it). Next, look at is the injectors. One or more could be dirty on the right side. Should they be removed for cleaning, or run some Techron thru the tank? The GM Driveability manual says the MAF sensor could cause a lean (PO171) condition, but not set a MAF error code. They suggest disconnecting the wiring, to see if the problem goes away. Can the plug wires be replaced without removing the water pump? Does anyone have any different suggestions, or a change in the order of the testing? Thanks you your help.

 

Likely a failed o2 sensor.