Ideas To Trace A High Rpm Issue

varunatech · May 10, 2012

Experts, I am trying to zero down on a problem shown by a Toyota 1NZ-FE engine at cold starts. Following is the background.

Engine: 1NZ-FE 1.5l YOM 2003 110k kms.

Air Filter: New

Tuning: Recently done

Throttle Body: Clean

MAF Sensor: Clean and ok

Plugs: Good

Fuel Consumption: Normal and Good

Engine Oil: Toyota, good condition

Overall: Well maintained

Fault Codes: No Fault Codes

Symptoms: "ONLY" on "some" cold starts, the engine revs to 2200 to 2400 RPM. And get settled after warm up.

Mind you this is NOT the usual engine warm up and self diagnostic routine, where RPM goes to 1800 and later settles. Please rule out that. This high RPM is beyond that.

And I detected a pattern after reviewing that this happens when and only car sits for more than 24 hours. If the car runs everyday and long distance, everything is ok.

Beyond this the user says at rare intervals and in traffic the engine try to go lower than 600 RPM and then kicks back. And this is rare.

Please comment.......with your views.

harshansenadhir · May 10, 2012

try replacing the idle control motor. Failing which, next culprit in most instances would be ECU itself. Try re-setting the ECU (search on web or follow the most common method. That is remove earth cable on battery terminal and press brake pedal for few times) whether would it help or result in changing of patterns

varunatech · May 10, 2012

On 5/10/2012 at 9:08 AM, harshansenadhir said:

try replacing the idle control motor. Failing which, next culprit in most instances would be ECU itself. Try re-setting the ECU (search on web or follow the most common method. That is remove earth cable on battery terminal and press brake pedal for few times) whether would it help or result in changing of patterns

Sorry forgot to include.......did reset ECU......and mind you this is not recurring. I also have suspicions on IAC Valve.

rather than jumping on replacing, I want to build a case and zero on with facts.

harshansenadhir · May 10, 2012

First try replacing with a one as a trial, may be a one from a working system. This always helped me in isolating which part is troublesome in this complicated EFI business.

varunatech · May 10, 2012

On 5/10/2012 at 9:24 AM, harshansenadhir said:

First try replacing with a one as a trial, may be a one from a working system. This always helped me in isolating which part is troublesome in this complicated EFI business.

Thanks buddy, it will help. But I really would like to see where it comes from and to find out based on theory. What makes it does this only on long stops. What does change in long stops.

Because the pattern is clear...............

invisibleuser · May 10, 2012

I also experiencing this now a days.

Malaka2 · May 10, 2012

Try to reset the ECU. probably it got wrong data on previous reading.

1st remove the battery terminals

2nd turn on reading lamp or something that work without relay.

3rd wait for 1/2 hr, so the Electronic circuits Capacitors will drain its electricity.

4th turn the terminal cables back, And don't start. Check Air filter and Coolant, If everything ok then start.

5th let it run in idle for 5 minutes(Don't trottle)

6th Drive it in a flat road about 20Kms. Now your Sensors picking up right signals.

Next morning your RPM works fine.

varunatech · May 10, 2012

On 5/10/2012 at 11:15 AM, Malaka2 said:

Try to reset the ECU. probably it got wrong data on previous reading.

1st remove the battery terminals

2nd turn on reading lamp or something that work without relay.

3rd wait for 1/2 hr, so the Electronic circuits Capacitors will drain its electricity.

4th turn the terminal cables back, And don't start. Check Air filter and Coolant, If everything ok then start.

5th let it run in idle for 5 minutes(Don't trottle)

6th Drive it in a flat road about 20Kms. Now your Sensors picking up right signals.

Next morning your RPM works fine.

Please see my post, I have reset the ECU and also this does not occur every day.

Malaka2 · May 10, 2012

Did you reset the ECU with this method or just removed the terminal?

The Don · May 10, 2012

On 5/10/2012 at 11:28 AM, varunatech said:

Please see my post, I have reset the ECU and also this does not occur every day.

Varuna, even I suspect the Idle speed controller or ICV (I think different manufacturers refer to the same thing differently). I had a similar problem where the engine will race too high at the start but it happened every single time the car was started with the AC on.

Also have you plugged your car into a diagnostic system just in case it is reporting a minor problem? In my car the issue was the combination of a number of things including a defective ECU.

Can you start the car without the AC on and see if it still has similar symptoms.

varunatech · May 10, 2012

On 5/10/2012 at 1:34 PM, The Don said:

Varuna, even I suspect the Idle speed controller or ICV (I think different manufacturers refer to the same thing differently). I had a similar problem where the engine will race too high at the start but it happened every single time the car was started with the AC on.

Also have you plugged your car into a diagnostic system just in case it is reporting a minor problem? In my car the issue was the combination of a number of things including a defective ECU.

Can you start the car without the AC on and see if it still has similar symptoms.

AC or non AC the issue is same and it only occurs after a prolong cold period. More than 24 hours. Else everything is pretty normal and the power up diagnostics and procedure goes well. Yes will connect this to a scanner and see and I am planning to check the ICV as well.

Thank you for suggestions.

varunatech · May 10, 2012

On 5/10/2012 at 11:31 AM, Malaka2 said:

Did you reset the ECU with this method or just removed the terminal?

Malaka, I did reset the ECU the same way you have suggested.

NRX · May 21, 2012

What's the latest news on this Varuna ?

The Don · May 21, 2012

On 5/10/2012 at 6:45 PM, varunatech said:

AC or non AC the issue is same and it only occurs after a prolong cold period. More than 24 hours. Else everything is pretty normal and the power up diagnostics and procedure goes well. Yes will connect this to a scanner and see and I am planning to check the ICV as well.

Thank you for suggestions.

With some of these issues, you need a data logger rather than a one time diagnostic, because the problem is intermittent.