Pontiac Repair: Could temp engine surge, mass air flow sensor, mass air flow

Question
I have 2k pont gp se with a 3.1.Below 20F the engine surges like starving for fuel.Only during winter.Never summer.If I ease the peddle or I press enough to shift out of od I can prevent this.The car has 120k and has had a fresh tune(plugs,wires,coil pacs,oil change and air filter.It also has new fuel pump,and filter and regulator.The injectors have cleaned(by gm dealer)and #2 replaced.Other than that the car runs and drives like a much younger car.Could this be a sensor?The ses light is never on wile driving.Justduring systems check at
start up.Also the mpg is 30 or so.Thank you Vince


Answer
Hey Vince:

Well with as many miles as it has on it thare are few things it could be. Yes a sensor could be bad or going bad giving the computer bad info when you start it up cold. A engine or air intake temp sensor could be off by a bit and throwing off the fuel mixture. You could have a mass air flow sensor that's dirty and throwing off the fuel trim. The only way to see that is with a scan tool. you could have a dirty throttle body and plate that is a big factor for idle quality! Make sure this engine has a ac delco pcv valve and not a one size fits all valve! These fuel injectors are noted for deposits forming on them and they will cause a lot of issues. You said you had them cleaned but with what product? There is a new "more better" product that GM has that is used in pressure flusher assembly.The car is actually ran on the product it's not added to the tank. It works pretty good. The last possibility is carbon build up on the back of the intake valves On this engine it happens quite a bit. you can get a product called top engine cleaner at any Gm dealer and use that you have to run it through a vacuum line on the engine get 2 can of it. BG makes a pretty good product for this as well. What this issue is the carbon on the back of the valves acts like a sponge and it absorbs the fule instead of the mixture going into the combustion chamber so it runs lean for the first little bit untill it can't absorb anymore. there is also a gm product called fule treatmnet plus you can add to the tank as a maintence item. These are just a few ideas off the top of my head there are other possibilites as well. Good luck :]