OK, this may be a long story, but here goes...

This vehicle came to me as prep for state inspection. No MIL, but when I ran my scan tool, of course two codes were present. P0301 and P0171. Customer was complaining of small shake at cold startup and adding coolant every 2 weeks or so.

P0301 has been fixed with a fresh head gasket, as the gasket coolant leak was fouling the number 1 cylinder plug, causing the misfire at startup, also warped the head to the point where the plug sleeve had to be drilled out and an insert installed. Also new AC Delco plugs and wires installed.

P0171 was initially thought to be an easy fix. Initial inspection plainly showed a broken hard plastic vacuum line to the PCV valve. I also ordered a fresh air inlet hose to the rear rocker cover direct from GM, it was out of place as they often get bumped around due to air filter replacement. Fresh upper/lower intake gaskets were used (the metal Fel-Pro replacements) and new bolts throughout. Sprayed the intake and throttle body clean, ran the engine after everything is done and P0171 still pops up.

Well at this point I decided to recheck my tracks. I did note a cracked nozzle on the purge valve solenoid, another one has been ordered and should be in sometime today. I also replaced the o2 sensor on GP- car has about 90K miles. Upon rechecking the scan tool, long term fuel trim is running about 21%. The fault sets at idle, normal operating temp. Long term fuel trim does come down to about 3-4% when I give it some rpm's. I have checked all vacuum lines, sprayed throttle body cleaner around the intake and hoses hoping to locate a leak somewhere, all seems to be OK. I induced fuel rich condition to recheck the o2 sensor, it did exactly as it should, as well as watched the voltage cycle back and forth as it should. I also checked fuel pressure at the rail. KOEO, went to 59-60 psi. Running, stayed at 60 psi, spiked to about 62 psi doing a snap test. I am about to check the MAF sensor voltage and frequency.

Although the purge valve should be replaced and although I would like to say its something easy like its the fuel filter or fuel pump or some obscure vacuum leak under the manifold somewhere, my tests are leading me to believe that none of these things are gonna rectify the problem. I would like some feedback to help me identify what could be going on, and to see what have I missed. Thanks in advance.

Yonda Spradley
Technician/Owner
Spradley Professional Auto Repair
Mechanicsburg, Pennsylvania, USA