Jumping Revs when Cold Engine

[Janisz]

Outside temperature went below -1 celsius and my T25 revs started jumping when I started the engine in the morning, its been like this for 3 days now .. every single morning same thing. Everything was fine when weather wasn't this cold. Yesterday I changed coolant temperature sensor but that didn't help. 

I will attach a video to better understand my problem. Revs only jump after car have been sitting whole night and they are not stable for like 1-3 minutes then they are okey (around ~1,000 rpms) for rest of the day. I can start the car during the day and there won't be any issues. Only the first start in the morning causes these rev jumps. Ohh and I have also changed spark plugs recently. 

Maybe someone has experienced something similar? 

[furtula]

Have you tried reseting it?

Take Battery off for 10 minutes, reconnect, start, let idle for 10 minutes for the ECU to relearn idle settings, go for a short drive.

 

[Janisz]

No I haven't tried taking Battery off. Coolant temperature sensor needs reseting too? 

Guy on Facebook group said this is normal and it does this to warm up faster. But I have this car for 2 years now and I don't recall having this last winter. 

[furtula]

For the car to warm up faster it would start with 1800 rpm, then slowly drop to 1500, 1200, etc, that's the normal behavior.

What i suggested is the simplest thing to try, it just resets the cars ECU, so it relearn's idle positions again.

It's the first thing i would try anyway...

[Janisz]

Okey will try that. 

[mrfixer]

Cold idle rpm should be close to 2000rpm and then fall steadily as engine warms up.

I suggest begin with a thorough clean of the throttle body and Idle Air Control Valve. Use Throttle Body Cleaner and a toothbrush or similar. After cleaning, disconnect the Battery for 30 minutes and then let the ECU relearn the idle (with A/C and electrical loads off).

Check live data and fault codes with Techstream.

 

[Janisz]

I cleaned MAF sensor.

Changed coolant sensor.

Reseted ECU.

Throttle body was cleaned last year. Few days ago weather got warmer and was above 0 degrees. Everything was fine.. no rev jumps. As soon as minus degrees.. revs starts to jump. 

Any ideas?

[Gerg]

In the absence of anything else to try at moment, you could try this:-

The stepper motor for the idle control valve, if I understand your engine correctly, is the black plastic unit that sits at the bottom of this photo (taken off an eBay item). 

If your throttle body does look like this, you could try disconnecting the plug that goes on to it.  This will likely create an error code (which will eventually go away some while after you have reconnected it and driven the car etc.).  The car idle speed will be incorrect, so you may need to apply some throttle just to steady the engine.  If the revs no longer jump around independently of your throttle input, then maybe the stepper motor is at fault?

I had a similar problem with a 2001 Corolla 1.4 vvti.  When the engine was cold (not the weather) the tickover was poor, but after about 2 minutes of running it all corrected itself. It would not fail again until the engine was properly cold.  I confirmed the fault by spraying the stepper motor with Freezer spray, which caused it to go wrong again.

Alternatively, you could put a hairdryer just on to this part before the engine is started, and see if the fault is better.

The stepper is attached by some five-pointed anti-tamper fasteners (why???) which are difficult to remove.  Also, the chamber that the valve sits in could have some muck in it that is independent of the throttle butterfly itself.  Could this be jamming the motor when it is cold/thick?

I replaced just this stepper motor with a secondhand one six years ago, it has never gone wrong since.  I also replaced the bolts with some other ones I already had (shown with a slight blue colouration in the next pictures).

But, on the Corolla an error code was eventually triggered as the engine warmed up, which you don't have.

tures.

[mrfixer]

4 hours ago, Janisz said:

I cleaned MAF sensor.

Changed coolant sensor.

Reseted ECU.

Throttle body was cleaned last year. Few days ago weather got warmer and was above 0 degrees. Everything was fine.. no rev jumps. As soon as minus degrees.. revs starts to jump. 

Any ideas?

I still think you have a fault with the throttle body/idle air control valve. Remove the IACV and clean it thoroughly.

[mrfixer]

1 hour ago, Gerg said:

In the absence of anything else to try at moment, you could try this:-

The stepper motor for the idle control valve, if I understand your engine correctly, is the black plastic unit that sits at the bottom of this photo (taken off an eBay item). 

If your throttle body does look like this, you could try disconnecting the plug that goes on to it.  This will likely create an error code (which will eventually go away some while after you have reconnected it and driven the car etc.).  The car idle speed will be incorrect, so you may need to apply some throttle just to steady the engine.  If the revs no longer jump around independently of your throttle input, then maybe the stepper motor is at fault?

I had a similar problem with a 2001 Corolla 1.4 vvti.  When the engine was cold (not the weather) the tickover was poor, but after about 2 minutes of running it all corrected itself. It would not fail again until the engine was properly cold.  I confirmed the fault by spraying the stepper motor with Freezer spray, which caused it to go wrong again.

Alternatively, you could put a hairdryer just on to this part before the engine is started, and see if the fault is better.

The stepper is attached by some five-pointed anti-tamper fasteners (why???) which are difficult to remove.  Also, the chamber that the valve sits in could have some muck in it that is independent of the throttle butterfly itself.  Could this be jamming the motor when it is cold/thick?

I replaced just this stepper motor with a secondhand one six years ago, it has never gone wrong since.  I also replaced the bolts with some other ones I already had (shown with a slight blue colouration in the next pictures).

But, on the Corolla an error code was eventually triggered as the engine warmed up, which you don't have.

Yes I agree. You are describing the idle air control valve