Problem on cold start

MARK87

MEMBER
2010 HYUNDAI I20
1.4L
4 CYL
2WD
MANUAL
125,000 MILES

Basically when you start the car the RPMs go up to 1,000, then after a 1 minute or 2 it goes down to around 860 RPMs which is normal RPMs, but during this 2 minutes if you press the gas pedal you can feel a misfire or a bit of rough idle which makes it difficult to get power from the engine, client a told me that the agency advise to change the IAC valve. Took the car checked the spark plugs which were okay, cleaned the throttle body and IAC valve nil fix. I also notice when you first start the car it won't hold idle it will just shut off, but after a second attempt it will start. Client also complained about getting low fuel mileage.
Will an IAC valve go bad without throwing a code? Any suggestions where I can start off? How to confirm if the IAC valve is the culprit? Would the IAC valve cause low fuel mileage?
I put the scanner there was no code found status was okay.

I have another client with the same issue but for her it's just the loss of power within the 2 minute period on cold start.

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

There are a number of things that can cause this, but we need to start with the basic things that can cause this. That means we need to find out if we have a fuel pressure issue using this guide to help with this:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

We need to know what the pressure is when this issue is happening and then we need to check for a vacuum leak when this is happening as well.

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

More than likely you will find a vacuum leak but if not, we need to put a vacuum gauge on the engine and that will tell us if we have an intake valve issue as well which would cause all these issues.

Below is a chart that will show what the vacuum gauge should be, and issues based on what it is doing.

So, let's run through this and we can go from there.

Thanks

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Monday, April 11th, 2022 AT 7:54 AM

MARK87

MEMBER
61 POSTS

Will go for the fuel pressure test first. Is there such a switch called " cold start switch" on all modern engines? A colleague was saying to check for a cold start switch which can cause this problem during a cold starting.

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Thursday, June 9th, 2022 AT 11:00 AM

KASEKENNY

MECHANIC
18,907 POSTS

No. Sounds like they are either messing with you or talking about something different and just calling it this name.

There definitely isn't a switch that you would flip that would cause the engine to start differently when it is cold.

The PCM handles all this by using the temperature sensors and determining the best way to start the engine.

If they can provide more info on what they were talking about then I am sure I can help figure out what they may be talking about.

Thanks

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Thursday, June 9th, 2022 AT 12:29 PM