I originally had this post in General, but it really belongs here. My 95 convertible with 90k miles was idling rough and I was getting a code 32, 63, and 64, using my Auto X-Ray scanner. 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:
• Replace 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.
• Look at is the right side O2 sensor. Check the wiring, and perhaps replace the sensor (why didn’t the dealer change it). Should both right sensors be replaced at the same time?
• 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 Drivability 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. Has that worked for anyone?
• 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.

 

Yes--unpluging will work if it's bad --you should notice immediate idle improvement---since you say you smell raw fuel---check the fuel pressure regulator( connected to the fuel rail)---pull the vacuum line off the regulator if you see/smell fuel at the nipple of the regulator or vacuum the diaphragm could be ruptured---could cause your problem---it would also drive a O2 sensor out of range--just another thought.