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Discussion Starter #1
Not sure whats wrong. I can be going 65 and it will start surging. I can feel it in the pedal. Rpm jumps back and forth while surging. Code was P0455 Large Evap leak. Change evap canister valve,MAP sensor,Purge Solenoid Valve,Throttle body,new gas cap and it's still doing it. Have not checked the brake pedal position sensor yet.
 

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Did the code clear? Any codes now? How many miles on it and have you changed the plugs. I kind of doubt it is the accelerator pedal position sensor.

About the only suggestion I would have would be to try to catch some live data when you are experiencing the problem, if you have a scanner capable. Does it seem to slip when the rpm's are jumping around? With the problem being specific to a certain speed would seem a possible trans issue.
 

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Discussion Starter #3
Before any of this happened I had codes P0097,P0113,P11C2,P228. Got purge solenoid,MAF sensor,Evap canister valve and those codes left and never came back. Yes I cleared the codes. None are on now but the engine light eventually comes back on woth code P0455. It's got a hard start as well. Same code keeps showing. Large evap leak. My symptoms are
1.Hard start
2.Nozzle clicking while pumping gas occasionly
3.RPM jumping
4.Feels like I have to use more pedal pressure
5.Clicking by back end possibly evap hose
6.Idles a little high when starting then it gets quiet.
7.Oil inside vacuum hose attached to throttle body. When I disconnected throttle sensor I can see the wires on the pigtail. Don't seem broken but Im pretty sure they'll eventually touch. Inside sensor was oil all over connection. Don't wanna move it too much. Seems it could break.. I cleaned it.
8. PCV valve is attracting oil.
155K miles no issues til now. Keep everything changed. Never had spark plugs done but I have some now.
 

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Discussion Starter #4
I have a code reader. I was in park while car was running to get this reading
Data Stream
Fuel Sys1 CL
FuelSys2 CL
Load_PCT 16.1%
ECT 101 degrees Celsius
SHRTFT1 1.6% to 5.5 to 4.7 to 0.0 etc
LONGFT1 28.9 STEADY NOT CHANGING
SHRTFT2 0.8% to 1.6 to 0.8 to 0.0 to 3.9 etc
LONGFT2 35.9% STEADY
FRP 360kpa to 381 Kia
MAP 35.0kpa STEADY
RPM 660.685
VSS Okm/h
SPARKADV -2.0-4.5
IAT 48-50 degrees C
MAF 3.30-3.52 g/s
TP 14.5% STEADY
Air_Stat OFF
O2S11 0.070v to 0.080v to 0.07v to 0.190v
SHRTFT11 1.6% to 7.0% to 7.8% etc
O2S12 0.650V to 0.665v
SHRTFT12 99.2%
O2S21 0.715V
SHRTFT21 1.6% TO 5.5% to 2.3% etc
RUNTM 776 Seconds
MIL_DisT 0km
FRP 3290kPa to 3160kPa
EVAP_Pct 14.9%
Fli 25.9%
Warm ups 18
CLR_Dis 584km
VP 60.8pa
Bark 100kPa
CATEMP11 512 degrees cel steady
VPWR 13.92V to 13.82V
Load_Abs 14.1%
LAMBDA 0.999 STEADY
TP_R 3.9%
AAT 4 degrees cel
TP_B 14.5 %
APP_D 19.69%
APP_D 9.8%
Tac_pct 5.9% to 5.5%

Evap Monitor 0.090"
Component $40.00
Limit type: min + max
Value 425.25
Min 0.0
Max 425.00
Status:FAIL🤔

Purge flow monitor Pass
Sensor heater B1-B2 Pass
Secondary air 1 pass
Misfire Cylinder 1-6 All Pass
 

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Have you changed the vent valve solenoid back by the fuel filler pipe? Purge valve solenoid underhood?
 

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I think you are going to have to take it into a repair place with a smoke tester. Possible a line broken or cracked?

Pat
 

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Did you change those components yourself? It sounds like possibly when the components got changed, a hose was left disconnected or broke. You fixed your old codes but introduced a new one. I would be looking over the work that was done before I started replacing other parts.
 

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Discussion Starter #9
I had about 4 codes to begin with. After changing all those things I was still stuclk with P0455. However I just changed my throttle bottle. At the connector I can see wires. They have a little oil on them. I didn't wanna move them too much so noting would break. I think it should be replaced. Oil was inside connector when i took it off as well. I cleaned it up pretty good.
 

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That sounds like a problem I had once with a bad torque converter lockup solenoid I had. It would kick in and out and rpms were all up and down and car would lunge. Never had a code for it but replacing the solenoid in the tranny ended the issue. Only happened at highway and cruising speeds.
 

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Put a
Not sure whats wrong. I can be going 65 and it will start surging. I can feel it in the pedal. Rpm jumps back and forth while surging. Code was P0455 Large Evap leak. Change evap canister valve,MAP sensor,Purge Solenoid Valve,Throttle body,new gas cap and it's still doing it. Have not checked the brake pedal position sensor yet.
FUEL FILTER
 

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Put a FUEL FILTER in it!! If you are afraid to move the wires then you shouldn't work on it. The wire braids not the wire usually harden and break! The wires dont! If they do, then replace that part of the harness. Use CRC electrical cleaner on wires and connectors. Does it surge with a FULL TANK? Put a Fuel filter in before you do anything else...
 

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Put a FUEL FILTER in it!! If you are afraid to move the wires then you shouldn't work on it. The wire braids not the wire usually harden and break! The wires dont! If they do, then replace that part of the harness. Use CRC electrical cleaner on wires and connectors. Does it surge with a FULL TANK? Put a Fuel filter in before you do anything else...
The 2012 Chevrolet Impala does not have a separate, serviceable fuel filter. The filter is part of the fuel sending unit module, mounted inside the fuel tank. The filter is “self cleaning”, as it sheds any fine debris that it stops when the engine is turned off.

If the vehicle is flex-fuel (I previously bought a new 2012 Impala LTZ model which was flex-fuel) - there were problems with the flex fuel-sensor, which caused the car’s computer to adjust the fuel trims based on the type of fuel the sensor was reading (full gasoline, E-10 or E-15 gasoline, or E-85 ethanol). It the sensor was bad, it caused drivability issues.

A previous poster also suggested having a smoke-test done - good advice. This should tell you where the leak is, since you have the code return for a large leak.
 

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First thing I thought of was using a vacuum gauge but I figured I would look in a Haynes's Manual first and I found this under Trouble Shooting: No. 12, Title; Engines surges while holding accelerator pedal steady. The items are #1 Intake air leak, #2 Faulty fuel pump, #3 Defective Throttle Position Sensor, and #4 defective ECM. If it was me, I would check #1 with a vacuum Gage and then check #3. I have had throttle positions do that kind of thing, but it was on a Ford. Hope this gives you a start on finding the problem. These modern cars have a lot of vacuum hoses and the heat can get to them. A vacuum Gage is one of the first mechanic's tools and engines are still basically air pumps.
 

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P0455 doesn't absolutely mean there's a big leak.
The code is set when the computer is not able to pull the fuel tank pressure down to the engineered value for the EVAP readiness test.
The PCM runs the EVAP test by setting the vent valve at the tank closed, setting the purge valve duty cycle to @20% IIRC, and monitoring the fuel tank pressure sensor for a preset negative pressure in a set number of seconds.
If the vent valve leaks, the fuel cap leaks, or the tank or fuel vapor system has sprung a leak somewhere it'll set P0455 and maybe others.
P0455 can also set when the tank pressure sensor has either failed completely or is no longer operating in calibration.

Plug in your Bi-directional OBD tool, start the car, and go to the EVAP testing section. Check that the tank pressure reads 0" Hg with the fuel filler cap removed. If the tank reads positive or negative pressure of more than 0.01" Hg with the filler cap removed the fuel pressure sensor is likely shot.
Assuming the tank pressure sensor is reading zero when it should be.
1- Put the filler cap back on and tighten it three clicks.
2- Command the Purge valve duty cycle to 40%, command the vent valve closed, and watch the tank pressure drop. If the tank pressure doesn't change at all the fuel tank pressure sensor is likely knackered. Remove the filler cap as a sanity check. It should make a sucking noise as it releases vacuum in the tank. If it doesn't suck vacuum when you remove the cap find the leak in the tank, filler neck etc.
NOTE; You can usually hear a sucking noise from a leaking filler cap or a leaking vent valve intake when you run the purge test.

I'm not sure the fuel tank pressure sensor can be replaced separately from the fuel pump/sender module... they may be a single unit. Some are and some are not.
 
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