Had a former GM tech get codes, mass air flow sensor and #6 cyl miss fire. Replaced the plugs and wires, didnt help. Engine starts skiping @ 4000 rpm feels like a rev limitor but not all the time. Bad fuel milage and loss of power. Has a 3800 supercharged engine
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Have it tested with a scan tool ,check engine sensor data parameters ! Possible dirty or bad mass air flow sensor ,O2sensor ,Coolant temp sensor, map sensor etc... Check for vacuum leaks , Plugged fuel injectors , dirty throttle plate , also check fuel pressure . Is your check engine light lit ?
Your car cold start valve puts more gas into the system keeping your engine running higher RPM. When you car warms up, the cold start valve will stop working and your car RPM will drop. What you could have is a vacuum hose disconnected which puts more air into your engine - therefore when you press on the gas pedal, your engine would shut off or you find lack of power and then shut off.
check engine light will not go out or codes cleared till computer is cleared so if you have set off a code while trying to diagnose it will stay in memory with that in mind
PO171 & 174 are related to bank 2 lean o2 sensor reading high oxygen in exhaust at sensors PO120 has to do with throttle position sensor input out of range PO306 is a misfire in #6 cylinder
in my opinion any miss will cause o2 sensors to read lean because the cyl is in effect a air pump sensors only pick up o2 not the fuel does you engine run rough or hesitate/shaking on acceleration i would check coil wire and plug for #6 also the injector not working will cause miss also they look ok do compression test on cyl will read 150psi if you find cause of miss you will be able to diagnose lean
with the tps sensor check to see if the connector was disconnected at any time you were testing
basically you need to isolate misfire and fix then have the computer cleared of codes drive car and if engine light comes on then we will go through test procedures for new codes
i hope this helps you to get a few ideals on how to proceed good luck ley me know
check aux air control valve , thats what controls the idle it may be bad,also with that kind of mileage i would replace the mass air flow sensor ,do that first, good luck , the mass air flow sensor has alot to do with your gas mileage .
Well there are several things that could cause this problem...
1. one of the coils may not be firing.
2. the ignition module could be bad.
3. the mass air flow sensor could be tellign the car to run rich (too much gas)
4. if the car is equiped with a map sensor it could do the same as a mass air flow sensor.
5. fuel pressure regulator could be leaking at vacuum port drawing in more fuel than needed.
6. the computer itself could be bad as well.
The car either has a map sensor or mass air flow not both. The mass air flow would be right after the air cleaner housing usually a 4 wire connector. map sensor is normally located on the rear of the upper intake manifold with 1 vacuum line going to it with 3 wire connector. Hope this helps.
fuel pressure regulator on the fuel rail is probably it or the egr valve is stuck open allowing burnt fuel to flood the intake, im leaning towards the fuel pressure regulator because the o2sensor is probably reading rich or if its reading lean then i would choose the egr valve . good luck