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P0191, too low fuel pressure on idle etc.


Arttu_T
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Hi guys!

I am new in here and my English is not perfect, don´t judge me please :D 

My car is Toyota Avensis T25 2.4L 2004 Automatic-transmission

So my problem(s) are these:

- On cold start, temperature approx 10 Celsius. When i start my car the idle goes wild. Revs change from 800 to 1000 or so, very quickly. This happens like 0.5 intervals. Revs go up and down 2-6 times an then idle settles down to normal speed 800 or so but does not change. Sometimes i get P0191 code

- When driving, warm engine. Decreasing speed to a full stop in traffic lights. Idle starts changing for +-100 revs, MIL-light shows up when it drops down like 150, to 650-600 rpm code P0191. When accelerating sometimes car goes to limp mode, sometimes not. When i lift the throttle up and press again once or twice the limp mode deactivates and i get full power. 

- I did get my hands to OBD tester that did read fuel pressures. On cold engine idling the pressure was 8-9MPa, but on warm engine pressure drops to 7MPa. When i press the pedal just lightly like 1millimeters, the pressure builds up to 8MPa. When revving the pressure reads at 14MPa. 

-The MIL-light checks itself sometimes when ignition is switched off for several hours. 

So what would cause the problem... I have thinked that maybe some moisture in connections in engine bay... Is the idle too low? Workshop manual says that fuel pressure should be from 8 to 14MPa. 

Do anybody had same problems?

I appreciate your thoughts and comments!

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Changed the Battery recently?

That sounds like you disconnected the Battery, and upon reconnecting you did not let the car idle for 10 minutes, if this is the case, disconnect Battery for 10 minutes, reconnect, let idle for 10 minutes, take for a short drive.

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23 hours ago, furtula said:

Changed the battery recently?

That sounds like you disconnected the battery, and upon reconnecting you did not let the car idle for 10 minutes, if this is the case, disconnect battery for 10 minutes, reconnect, let idle for 10 minutes, take for a short drive.

Well i have disconnected the Battery after these problems occurred. Before that i don´t remember when i did  disconnect the Battery. I have not done this procedure ever when I have disconnected the Battery... And this is the first time this have happened. Why is that so important to let it idle for 10 minutes?

Yesterday i did clear the code and it did not show later on that day. I haven´t drived since that day. But i will do this procedure to my car to see if that helps. Do i need to put it in gear or turn the key twice or something like that before 10 minute idle?😄

My dad did say that this car have had allways too low and wavy idle and had vibrations due it. In Toyota dealership mechanics they did just raise the idle speed after dad said these symptoms😄 (we have had this car for at least 10 years)

Thanks! Any other thoughts? 

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Symptoms you described reminded me of replacing the Battery, but not letting the car do the re-learn procedure after that, which is the 10 minute idle thing.

Anyway it does not hurt to try it, as it resets the ECU and it has to learn idle values again etc.

No special procedures, just take negative terminal off for 10 minutes, reconnect, start car and let it idle for 10 minutes.

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8 hours ago, furtula said:

Symptoms you described reminded me of replacing the battery, but not letting the car do the re-learn procedure after that, which is the 10 minute idle thing.

Anyway it does not hurt to try it, as it resets the ECU and it has to learn idle values again etc.

No special procedures, just take negative terminal off for 10 minutes, reconnect, start car and let it idle for 10 minutes.

I did try this method. No MIL-light when started, idled like 2-3 minutes and the light came up. P0191 code.

Now it did shut it self down once when idling with MIL-light on. 

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A quick search for the code gives "Fuel Rail Pressure Sensor Circuit Range/Performance". This could mean that the sensor is at fault or possibly clogged or dirty. You should probably check the fuel filter and replace it if needed, and check the fuel tank pump pressure with a gauge. Then try to diagnose the sensor and it's wiring and connector. Idle air control valves and dirty throttle bodies can also cause idle problems like this. Another source of problems with idle speed could be problems in the oxygen sensor systems, leading to the short term fuel trim values being wrongly adjusted. Have a look at those with your diagnostic tool, if you can. Is that a petrol or diesel engine, by the way?

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51 minutes ago, paul9 said:

A quick search for the code gives "Fuel Rail Pressure Sensor Circuit Range/Performance". This could mean that the sensor is at fault or possibly clogged or dirty. You should probably check the fuel filter and replace it if needed, and check the fuel tank pump pressure with a gauge. Then try to diagnose the sensor and it's wiring and connector. Idle air control valves and dirty throttle bodies can also cause idle problems like this. Another source of problems with idle speed could be problems in the oxygen sensor systems, leading to the short term fuel trim values being wrongly adjusted. Have a look at those with your diagnostic tool, if you can. Is that a petrol or diesel engine, by the way?

This is petrol engine so the fuel filter is in the fuel pump, in a gas tank... Can you give any spesific guides how to do these? I need to get a gauge from somewhere. I have been looking for how to change the fuel filter element but havent found any good ones yet.

Is there any limit range/bounds to sensors? Only what i have found was the fuel pressure 8-14MPa. And it was in that range, allmost the whole time 😂

And the fuel pressure sensor is under the intake manifold... 😂

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