2004 corolla rough idle p0505. Air sensors changed throttle body too. Heater starts problem

[corolla-er]

Hello everyone. I am trying to help my friend find the cause of an issue of his car.

So he has been having issues with rough idling, then it go so bad it would make the engine splutter and stall. Got error p0505

Then replaced air sensors, no fix, then changed the throttle body, it has SORT OF fixed it.

So now the car will idle fine, until heater is activated. Then this will start making the idle rough, going up and down between 7.5-1050rpm. Giving it some rev sometimes sorts it but not all the time.

How is the heating system connected to the idle system? Is there crossed wires somewhere? Does someone have wiring diagram?

 

I dont suspect it to be a vacuum leak, as it can be activated electrically via the heater. Now there is a noise when I open the fuel tank from releasing pressure, that didnt happen before, should it? Again we have changed the throttle body and the air sensors. Where to check next? Any help appreciated 

[oldcodger]

Hi,

The heater causing the problem is probably down to the electrical power its taking or there is some kind of short in the wiring loom affecting both circuits ?

Try putting the headlights/full beam/rear screen heater  on instead, does that cause the same problem ?

Quiet a bit of info around on that error code , plus  -

https://www.way.com/blog/p0505-error-code/

 

 

 

[corolla-er]

1 hour ago, oldcodger said:

Hi,

The heater causing the problem is probably down to the electrical power its taking or there is some kind of short in the wiring loom affecting both circuits ?

Try putting the headlights/full beam/rear screen heater  on instead, does that cause the same problem ?

Quiet a bit of info around on that error code , plus  -

https://www.way.com/blog/p0505-error-code/

 

 

 

Excellent thanks for your reply! I will get him to try these and report back. Thank you again !

[corolla-er]

Also any photos of the wiring diagram?

[oldcodger]

From a 2004 US corolla manual, should be very similar to yours apart from the actual engine/LHD

Good practice to check your Battery is sound, its terminals and importantly its chassis Earth connections in the engine bay etc.

A poor connection may be reducing the power available, causing the problem when you add  the extra load of the heater etc.

 

10 - Engine Control System.pdf

[corolla-er]

Hi thanks for your help.We have been doing some testing. using your information and some from google too

We have tested and checked the o2 sensor in exhaust, the air sensor in airbox. We have checked TPS on the throttle body and we have checked resistance of the motor for the butterfly valve. All is within spec, nothing seems out of ordinary.

Car will idle fine then it will start rough idling untill you turn the car off / on. SOmetimes it stays doing it after turning on / off sometimes not. Now putting heater on only causes issue sometime. The guy thinks it happens more when its warm

 

Also we had a faulty air sensor from before, which we put in which allowed us to remove the air pipe on the throttle body whilst its running. 

We can see that the butterfly valve is phsyically moving, and It is this action that is causing the rough idling.

My question is what can be causing the butterfly valve to move? Should only the foot pedal cause the butterfly valve to move? Or is there some system in ECU that has a cold start fuction or something

Does this mean throttle body is faulty? Or can it be something on the fly by system? Or maybe the ecu? What things to check moving forward?

Thank you again

[oldcodger]

Hi,

Well there is an Auto Choke function when you start the car up from cold, assume thats an ECU involked function via the temp sensors and would be turned off when warmed up.

The only catch with using second hand parts is you never know how good or bad they are and if they have new problems, unless they are off a working car ?

As in that pdf you can measure the resistance of the accelerator pedal control, but that does not always reflect runing condition.

Am not into this kind of troublshooting, but wonder if you would get some clues by using an OBD scanner where you can Live View various parameters, even cheapish scanners do some basic functions.

If not hopefully others will come in and help............

 

 

 

 

 

[corolla-er]

Hi thanks again. Yes that is what I was wondering. So even though the throttle body looks simple, and its components are within the paramaters for it to function... Sometimes they are just broken? So still replacing throttle body with one we know is weorking. This one was from a scrapyard 

[oldcodger]

Just one last thought from me,  your problem reminded  us of when the Battery has been disconnected for a while.

When power is restored the ECU goes into Learning Mode and for the first few miles the tickover is all over the place, sometimes even stopping/stalling until it works out the correct idle.

If you had been disconnecting the Battery, or had a bad Battery or connections /earth points ,wonder if that could be causing the ECU to reset and re-learn  and giving you those symptoms  ? 

Just a long shot... though have read in the forum a few other similar mystery engine problems cause by a poor  battery.