RPMs drop on the first startup of the day

YAZIDAN

MEMBER
2007 TOYOTA COROLLA
1.8L
4 CYL
2WD
AUTOMATIC
210,000 MILES

On the first start up in the morning, the RPMs goes approximately 2,000 which is normal however when I rev the engine the RPMs drops and the engine shakes it like when you put brake clean in the intake and start the car, and ounce white smoke with the smell of gas came out the engine (i think I have exhaust leak). It's like it flooded with gas. No codes, no check engine light and when the car acted up the check engine light did not flash. I checked the coolant level it's still same level and the oil is not milky.

7 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This could be a couple of things, so we need to start with some testing first.

When you first start the engine and it revs to 2,000 RPMs, does it stay there until you press the throttle?

If so, what happens if you don't press the throttle? Do they stay high and then slowly come down as the engine warms up?

when they are high, does the engine run poorly or does it only run poorly when the RPM drops? What do the RPMs drop to?

If you want to get a video of what happens with this then that could answer a lot of these questions.

However, I am thinking we have an issue with a vacuum leak that is not there when the engine is warm.

Here are a couple of guides that will help with this:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/engine-idles-too-high

Clearly this is going to be different depending on what we find with this.

So, let's start with a video of you pressing the throttle and then one of not pressing the throttle so that we can be on the same page.

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Thursday, February 3rd, 2022 AT 3:07 PM

YAZIDAN

MEMBER
107 POSTS

Yes, it stays at 2,000 RPMs until I press the gas pedal.
If I don't press the throttle the RPMs starts to drop slowly with no rough idle
it runs poorly. Only after I press the pedal and the RPMs drop to approximately 1,000.
Also, the car has no IACV. High idle is controlled by the electronic throttle body.

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Thursday, February 3rd, 2022 AT 4:32 PM

KASEKENNY

MECHANIC
18,907 POSTS

Okay. What is the temperature where you are when this happens? How long has this been happening? If you think about it, could it have started when the temperature dropped?

Basically, this is not uncommon on cold days because what is happening when the engine starts, the RPMs rev and try to warm the engine as quickly as possible. As the engine warms up, the idle will come down. However, if the idle comes down too quickly then the air fuel is off when it is cold.

If this has been happening even on warmer days, then there is another issue that is causing the air/fuel to be off. So, this would be a vacuum leak, spark plugs, or even injector issues.

So, let's start with this info and go from there.

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Thursday, February 3rd, 2022 AT 4:34 PM

YAZIDAN

MEMBER
107 POSTS

Very cold outside temperature about 25. I don't know if it does it when it is warm outside. When I start the car, it idles high, about 1,800 if I don't touch the gas pedal it will drop slowly with no rough idle. If I touch the gas pedal it will drop to approximately 1,000 and idle rough.

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Thursday, February 3rd, 2022 AT 4:38 PM

KASEKENNY

MECHANIC
18,907 POSTS

Yeah. This sounds like it is normal for cold weather starting.

We could have some other minor issues with worn spark plugs or even injector issues. However, at this point, I would start the engine and let it warm up for a few minutes and not touch the throttle.

However, then when it is warm outside, above 40 degrees, retest this and see if it has a rough idle when you touch the accelerator after you start it. If it doesn't then this is just cold starting. If it still does it then we should change the plugs and run some fuel cleaner through it to see how it does.