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Discussion Starter · #1 ·
Car: Elantra 2.0, sedan, M/T (stick shift)

Here is the scenario:

Common thing is that it is a cold start after overnight.
Also, my driving: I start, give it 5 seconds, take off. Then when I coast/roll to a stop in neutral... and here is what is happening.

Summer time (temperature above 35 F outside).
Idle will be around 900 RPM. When rolling in N at about 10 mph idle is say 900 RPM. I come to a complete stop - idle remains same.


NOW
Winter time (temperature below 30 F outside).
Idle will be around 1200 RPM. When rolling in N at about 10 mph idle is say 900 RPM. I come to a complete stop - idle goes UP to about 1500 RPM.
The colder the start, the higher the idle.
If ambient was 15 F - idle could go up above 1500 RPM at stop. When rolling in neutral (say on a small incline) at speed above 5 MPH idle will drop to 900 RPM.

Why?
What makes it to change and why does it change?
It just seems that engine is revving up when I come to a stop.

A solution to it is to... restart engine once its temperature is above 35 F. That makes it more weird to me...
 

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higher idle in the cold when the engine is still cold is very normal. cold air has a higher density so the ECU is forced to add more fuel. partially why your fuel economy sucks in the cold. some cars will tweak the idle a bit higher in the cold to try and warm up the engine faster - cold is when you are wasting the most fuel. i'm not sure if that is the case here or not.

once the engine warms up the idle should drop back down...it shouldn't take long. are you saying the idle is staying high until you turn the car off then back on again?

see if a code scanner gives you any clues...i'm a little unsure as to your description of the problem.
 

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Discussion Starter · #3 ·
higher idle in the cold when the engine is still cold is very normal.
Thanks for input.
Yes, I know that higher idle is normal on cold.
I use ScanGaugeII and there is no codes.

I guess I must take a video of it...
But let's try again.
What I'm saying is that - imagine what I am doing.
I am parked on slight incline. I get to the car, start engine. Idle settles at say 1500 RPM (it is cold, 25 F). I take my foot off the brake and the car starts rolling.
Then idle suddenly drops to about 900 RPM. I do not touch the gas.
I stop. Idle goes up to 1500. I let it roll - idle drops to 900. I stop again - idle goes to 1500... and so on.

So, what does that mean?



I have V6 KIA Rondo. It does not do that. Idle is higher the colder it is, but it is not affected by speed. Although this one is A/T.
 

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i'm going to hold out for a bit of input from other members here. i simply don't have enough hands on experience with that engine to say if that is normal or not. seems odd, i'll give you that. your second description was much more helpful. without any codes to go on.....i would try simply resetting the ECU by pulling the battery cable for 20 mins. easy and doesn't do any harm.

when the engine is fully hot does the idle still stay high?
 

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Discussion Starter · #5 ·
when the engine is fully hot does the idle still stay high?
I'm glad you got what I was trying to describe.

Here is the catch - when it does it (idle higher at stop) I can restart the engine and idle will be OK. I only must restart it when coolant temperature is higher than 35 F. Then it acts fine - no elevated idle at stop.

To answer your question - yes, when it is warm, it is fine. At least I think so.
It will idle at about 650 RPM at stop, while when rolling idle goes up to about 900 RPM. I think this one though, is normal condition. I think...

I am at complete loss as I can't really chase it. I got nothing to catch on.
TPS readback is constant. All other parameters are fine (closed loop, ignition...).
 

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I'm leaning toward the coolant temperature sensor. Check your wiring, I'll have to get you the link for the repair manual. If you hunt around I've posted it plenty of times.

You can use a multimeter to figure out if it's working right. Very easy, just takes a little time.
 

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Discussion Starter · #7 ·
I'm leaning toward the coolant temperature sensor. Check your wiring, I'll have to get you the link for the repair manual. If you hunt around I've posted it plenty of times.

You can use a multimeter to figure out if it's working right. Very easy, just takes a little time.
It reads reliable temperature.
I use ScanGauge to give me exact reading.
Ambient can be -10 C, engine will be -8 C. When at operating temp it is +82 C. Fan kicks in at +95 C. Hence, I'd say it is OK.
With it completely disconnected - it will read -40 C and engine goes to some "fault mode" not knowing what is the true temp.
 

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These cars I believe use an IAC . sometimes these need to be cleaned or they do occasionally malfunction.
 

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Discussion Starter · #9 ·
These cars I believe use an IAC . sometimes these need to be cleaned or they do occasionally malfunction.
I do not argue they do not need cleaning; however, this is a permanent issue. It has been acting like this since day one (as the second owner).
It is not a randomly occurring issue - it is temperature driven.

I am trying to understand it and find out if there is a way to alter this behaviour.
When on very cold day I come to a stop and idle smoothly, but quickly, goes to 1500 or 1700 rpm (as I said - the colder the higher idle) then it looks... weird to have engine running at so high speed.

I know we have some experienced service folks here. Would you chime in?
 

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Discussion Starter · #10 ·
So here is a video of what is happening.
I recorded it in on one morning where outside was -10 C (14 F). Maybe this will help to understand what is happening.

So guys, now when you see it - any suggestions?
The thing is that I have no one to compare it to. My friends Touring, which is A/T does not do that. The best would be M/T sedan... but nothing here.
@dtech, you said IAC valve - it would show its issues some other way as well, right?
@zero_gravity, I checked coolant. No problems there. Unless you disconnect the sensor and it goes to -40 C and after a minute gets crazy, because, what I think, it knows it had enough time to rise the temperature and it does not see it.
@sbr711, you seem to work for Hyundai, so maybe you have some cars to compare it to?

 

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if it was my car I'd be looking at a lot of different areas to try and identify the problem and eliminate some possibles causes:

bad or dirty maf
vacuum leak - yes they can sometimes be small and effects only noticed in cold weather, like manifold vacuum leak
check IAC - operation - is current being applied to the valve when your idle jumps
operation of coolant temp sensor, is ECU getting a consistent signal

also I'm not sure about this engine but many engines operate in open loop until the temp sensor signals the engine has reached a certain temp, then it switches to closed loop and the O2 sensor comes into play to adjust the mixture. So things a bad MAF signal or vacuum leak could cause the ECU to be making adjustments that raise idle speed.

that's all I can tell you, good luck !
 

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if it was my car I'd be looking at a lot of different areas to try and identify the problem and eliminate some possibles causes:

bad or dirty maf
vacuum leak - yes they can sometimes be small and effects only noticed in cold weather, like manifold vacuum leak
check IAC - operation - is current being applied to the valve when your idle jumps
operation of coolant temp sensor, is ECU getting a consistent signal

also I'm not sure about this engine but many engines operate in open loop until the temp sensor signals the engine has reached a certain temp, then it switches to closed loop and the O2 sensor comes into play to adjust the mixture. So things a bad MAF signal or vacuum leak could cause the ECU to be making adjustments that raise idle speed.

that's all I can tell you, good luck !
in a nutshell sounds like it could be a fuel trim problem which the ecu tries to correct - do you have the equipment to check the AF trim and verify ?
 

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Discussion Starter · #13 ·
bad or dirty maf
vacuum leak - yes they can sometimes be small and effects only noticed in cold weather, like manifold vacuum leak
check IAC - operation - is current being applied to the valve when your idle jumps
operation of coolant temp sensor, is ECU getting a consistent signal

also I'm not sure about this engine but many engines operate in open loop until the temp sensor signals the engine has reached a certain temp, then it switches to closed loop and the O2 sensor comes into play to adjust the mixture. So things a bad MAF signal or vacuum leak could cause the ECU to be making adjustments that raise idle speed.

that's all I can tell you, good luck !


in a nutshell sounds like it could be a fuel trim problem which the ecu tries to correct - do you have the equipment to check the AF trim and verify ?

To answer both comments:
MAF is clean as pearl
No vacuum leaks
IAC - works OK. There is no rough idle, no sticking valve.
How consistent coolant temp signal is - I am not sure, but using ScanGaugeII I can tell readback is steady.

It goes to CLOSED loop within 10 seconds. I was doing extensive check on closed loop with this one. Once it goes to closed loop in about 10 seconds from start it stays there no matter what you do - floor it, gently ride, sudden acceleration. Under only one condition it opens the loop - engine breaking. Cuts off the fuel completely and opens the loop.

Guys, you are looking on it on wrong side.
If you look in the video, when the car rolls down on the hill - once I restart it (with engine temp at about +30 C) it does not happen again.
That suggests me some programming issue.

I do not have any problems with the engine itself and its controls.
I'm looking for an explanation if ECU can be doing it, and if it does, how can I change it.

And it has been doing it since day one, meaning for the last 3 years I have the car. It is somehow related to coolant temp. I did not play with a resistor to trick ECU to think engine is warmer than it really is.
 
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