Runs rough till warmed up

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Oct 10, 2018
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#1
Make
chevy
Model
malibu
Year
2007
Miles
134.000
Engine
3.5
When I star it when it's cold it starts rough and the tach drops out. I read the codes and got a code for the MAF sensor so I changed it. I have changed the engine temp sensor, the wires and connector to the throttle position sensor, ran fuel injector cleaner several times and checked for eddy sparks through spark plug wires while it was dark (none seen). When the car gets warmed up to running temperature, it runs great. Right now the codes that I have are saying that bank 1 and 2 are running lean. When I started it today to let it warm up, it smelled like it was running rich. It's like the car has nothing to choke it for cooler weather. Any suggestions?
 

billr

wrench
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#2
Check fuel pressure? That's one thing that isn't usually available from live-data, which is my next suggestion. Live-data can let you check a lot of things and avoid much guessing and parts-swapping.
 
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Sep 11, 2018
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#3
Happy Friday! Let me start out by saying that computer codes only gives one the name of the street. It is up to the mechanic to figure out he exact street address. Replacing sensors just because they set codes get expensive and seldom solves the problem. Low fuel pressure can cause a lean condition, but so will too much air (O2). The engine running fine after it reaches normal operating temp is a key clue. When ever something gets hot, it expands. I suspect that's what's happening here. Check for vacuum leaks. One way to do this would be to spray throttle body cleaner around vacuum fittings, the intake manifold and throttle body. Listen for changes in engine idle. Malibu intake gaskets have/had a reputation for failure. Good luck.
 
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#4
Probably intake gasket. As Chester says use alternative fuel source and go around intake. They usually fail at the ends of the valley where rtv is used. The only thing is these areas USUALLY don't seal up from engine warming. Early on they MAY. You may want to use a propane torch, unlit, instead of carb cleaner. Either way if the idle smooths out you've found the area of the leak.