On a road trip with my daughters yesterday, I got the reduced power light on the cluster. This was after about 2 hours of highway driving. Pulled over and checked the codes. They are as follows:

P0128 Powertrain, Coolant thermostat. (I replaced the whole thermostat assembly last year. When It is under 40 degrees out I get this code.

P0201 Powertrain Cylinder 1 misfire

P0302 Powertrain Cylinder 2 misfire

P0300 Powertrain Random/multiple cylinder misfire

B2AAA Body

Recorded the codes and cleared them, was able to drive back home, no issues at highway speed. However, as soon as you slow down to stop I have a rough idle and it resets the codes. 124,000 miles, plugs last changed at 70K. Performed an oil/filter/air filter/cabin filter change day before. Running mobil 1 5/30 full synthetic.

Visually checked coils last night, no oil leaking into sparkplug tubes, no carbon tracing on coils. Check intake boot for cracks and leaks, none found.

here is the Freeze Frame Data after it set the code one time.

Freeze frame information:

------------------

Fuel Status = 0 byte

Engine Load = 38.431 %

Engine Coolant Temperature = 188.6 °F

Fuel Trim Bank 1 Short Term = -1.562 %

Fuel Trim Bank 1 Long Term = 10.156 %

Engine RPM = 819.5 rpm

Speed (OBD) = 1.243 mph

Timing Advance = 3 °

Intake Air Temperature = 80.6 °F

Mass Air Flow Rate = 4.25 g/s

Throttle Position(Manifold) = 16.078 %

Run time since engine start = 2,623 s

Fuel Level (From Engine ECU) = 86.275 %

Barometric pressure (from vehicle) = 14.649 psi

Voltage (Control Module) = 14.512 V

Engine Load(Absolute) = 34.902 %

Relative Throttle Position = 5.098 %

Ambient air temp = 55.4 °F

Absolute Throttle Position B = 16.078 %

Accelerator PedalPosition D = 14.51 %

Accelerator PedalPosition E = 7.451 %



Any suggestions?

 

Start by changing the plugs. They are overdue.

 

With other cars when short or long term fuel trims get in the vicinity of +/- 10% that's error code territory. A positive fuel trim -- long term fuel trim -- is the engine controller having to add fuel. Could be an intake air leak. An inspection may not spot the leak. In some cases the intake system is pressurized and filled with smoke. This makes the leak easier to spot.

In the old days using an aerosol can of Carb cleaner -- leaves no residue -- sprayed at various places of the intake system -- with the engine idling -- would be used. The engine reacts when the spray hits the leak.

Could be a weak injector. The engine controller adds fuel by increasing the injector pulse width of all injectors. This can make otherwise good cylinders act up, aka misfire.

I don't know what the plug change intervals are but if they are close then i like mini... advice to change the plugs is good advice. I'd be tempted to replace the coils too.(I replaced the coils -- no misfires -- just on general principles on another car -- with around 140K miles -- along with plugs even though the plugs were about 10K miles from being due. Afterwards the engine ran noticeably better. I had the plugs changed before on scheduel and the engine never reacted one way or the other. The new coils accounted for the improvement in how the engine ran. (This engine also ran better after I had all 4 O2 sensors replaced at 132K miles, but in this case one sensor was triggering an error. But the engine otherwise ran fine so the improvement from the new sensors was a bit of a surprise.)

If you change the plugs be sure you use the right plugs and double check the gaps.

 

Going to change the plugs and coils, car is parked till then. Will try and borrow smoke tester and see if we can spot anything. Anyone replace their Valve cover? I have changed the gasket, but reading a lot of threads of bad valve covers, or is that mainly on the turbo engines.

 

4 New NGKs 95770, and 4 new bosch coils later. Misfire cylinder 1 still. Rough idle. Highway speed no codes and not showing misfire. at idle, STFT 1.6, LTFT 21.1, at 70mph STFT -.08 LTFT 10.2.

Tomorrow hunt for vacuum leak.

Any suggestions appreciated

 

verified injectors and coils firing, then did compression test

compression test
1 0
2 150
3. 150
4 150

pulling valve cover and then probably intake and exhaust today,

 

Well that might be the problem.

 

Machine shop got back to me. Pressure checked, resurface and replace the one valve. Valve should be here this week, then hopefully get the head back by next weekend.