Hyundai Forums banner

1 - 20 of 21 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter #1
For about a year this car has had an idling issue where it refuses to idle the first minute after startup. I recently was told to look at the short term fuel trim. When I did I noticed that when it doesn’t want to idle the fuel trim is -2 to -12 and when it decides to idle it is steady on -29. If anyone has any advice on to what to check it will be appreciated. It has 230,700 miles and I checked the idle air control valve. I also replaced the MAF which fixed the issue for a week. There are no codes or lights.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #2
For about a year this car has had an idling issue where it refuses to idle the first minute after startup. I recently was told to look at the short term fuel trim. When I did I noticed that when it doesn’t want to idle the fuel trim is -2 to -12 and when it decides to idle it is steady on -29. If anyone has any advice on to what to check it will be appreciated. It has 230,700 miles and I checked the idle air control valve. I also replaced the MAF which fixed the issue for a week. There are no codes or lights.
This was one graph of a few this one is the most accurate.
441447
 

·
Registered
Joined
·
3,919 Posts
Just a few questions ....
When was the last time you checked the air filter?
Also, when was the last time you put in some fuel system cleaner into the gas tank?
When was the last time you cleaned the in-take plenum, throttle?
 

·
Registered
Joined
·
12,158 Posts
I'm surprised there are no trouble codes logged with so much fuel trimming taking place.

Before this idle fault developed where you having any trouble starting the engine after adding fuel to the tank?

Have you checked the engine temperatures on your scan tool data list? Are the intake air and coolant temperature sensors returning plausible values? Before the first start of the day these two temperatures should be the same or very close at least. And should be very close to the ambient air temperature too.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #6
Just a few questions ....
When was the last time you checked the air filter?
Also, when was the last time you put in some fuel system cleaner into the gas tank?
When was the last time you cleaned the in-take plenum, throttle?
The filter is clean. I haven’t put cleaner in the tank but I have cleaned the throttle body and in that area.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #7
I'm surprised there are no trouble codes logged with so much fuel trimming taking place.

Before this idle fault developed where you having any trouble starting the engine after adding fuel to the tank?

Have you checked the engine temperatures on your scan tool data list? Are the intake air and coolant temperature sensors returning plausible values? Before the first start of the day these two temperatures should be the same or very close at least. And should be very close to the ambient air temperature too.
The idle issue occurred about two months after I had the car. My mom had it before for five years. As far as I know she had no issue with idling. The intake and water temps are nothing crazy. I don’t remember intake temps but water was just under 200. I haven’t checked the temps when it’s off. I’ll be able to look at that Friday through this weekend.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #9
I
For about a year this car has had an idling issue where it refuses to idle the first minute after startup. I recently was told to look at the short term fuel trim. When I did I noticed that when it doesn’t want to idle the fuel trim is -2 to -12 and when it decides to idle it is steady on -29. If anyone has any advice on to what to check it will be appreciated. It has 230,700 miles and I checked the idle air control valve. I also replaced the MAF which fixed the issue for a week. There are no codes or lights.
I’m stupid for forgetting this but when the car is warmed up it starts without an issue and has no idling issue. The only time it doesn’t want to idle is when the car is cold.
 

·
Registered
Joined
·
5,231 Posts
I

I’m stupid for forgetting this but when the car is warmed up it starts without an issue and has no idling issue. The only time it doesn’t want to idle is when the car is cold.
What does the engine temp read cold?
 

·
Registered
Joined
·
12,158 Posts
it only ran for 5-10 minutes so it might of been open loop
There is no trimming of the fuel when the management system is operating in open loop control.
The fuel trim figures are usually fixed at 0% until the fuel system switched into closed loop. At least that's what they display on my professional scan tool in open loop.

Actually I have the data on the app but it looks not quite right
No, that doesn't look right. And it might explain the symptoms your experiencing.
 

·
Registered
Joined
·
3,919 Posts
Okay, air filter is not clogged, nor is the injectors stuck open longer than usual
And the throttle body has been cleaned.

There is an issue when the engine is cold.
Engine runs rich.
Hmm, what was the problem you're having?

Bear with me, I am still learning what goes on.
Oh, that temp data looks wrong.
It seems that your engine is running extremely hot
And probably should have boiled over.
Please correct me if I am wrong.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #15
There is no trimming of the fuel when the management system is operating in open loop control.
The fuel trim figures are usually fixed at 0% until the fuel system switched into closed loop. At least that's what they display on my professional scan tool in open loop.


No, that doesn't look right. And it might explain the symptoms your experiencing.
I have another cheapo scanner I’ll play with but I’m not sure what that will or won’t give me.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #16
Okay, air filter is not clogged, nor is the injectors stuck open longer than usual
And the throttle body has been cleaned.

There is an issue when the engine is cold.
Engine runs rich.
Hmm, what was the problem you're having?

Bear with me, I am still learning what goes on.
Oh, that temp data looks wrong.
It seems that your engine is running extremely hot
And probably should have boiled over.
Please correct me if I am wrong.
The issue is that the car won’t idle when it isn’t warmed up. When it decides to idle it has a short term fuel trim of -29. I’m hoping knowing what causes the negative short term fuel trim helps fix the idling issue for good. I’ve cleaned the idle air control valve and the throttle body and replaced the MAF. This is the more interesting thing. When I replaced the MAF the issue all together was fixed for a week. I didn’t have a scanner then so I have no clue what any readings were. Also I have almost all the service history since my family has owned the car since new.
 

·
Registered
Joined
·
12,158 Posts
The issue is that the car won’t idle when it isn’t warmed up. When it decides to idle it has a short term fuel trim of -29.
Sounds to me like the mixture is too rich to allow the engine to idle when the fuel system is operating in open loop. It will idle once it switches to closed loop (warm engine) because a lot of fuel is being trimmed away, weakening the mixture (negative trim figures). As I said earlier, no fuel trimming takes place in open loop.

AdaMerlock said:
I’m hoping knowing what causes the negative short term fuel trim helps fix the idling issue for good.
A quick and easy test I would try is run the engine until it is able to idle, then set up your scan tool to monitor short term fuel trim.
Now take a pair of long nosed pliers and use them to clamp the hose between the inlet manifold and the purge control valve.
See if clamping that hose makes a significant difference to the fuel trim figures. If the fuel trim goes more positive when the hose is clamped you may have a leaking purge valve, which could explain the negative fuel trim.
 

·
Registered
Joined
·
5,231 Posts
That graph of the coolant sensor is nasty. If that graph is accurate you need a new sensor. Once the engine is hot enough it probably reads correctly. Some go open cold and some hot and some get weird all over the place like yours looks to be. The fuel delivery is strictly governed by the coolant temperature, TPS, and RPM..
 

·
Registered
Joined
·
3,919 Posts
Did not think of that. Stuck open purge valve could be letting extra fuel into the intake
Making the mixture rich and the idle a hard time?

GRC is on the coolant temp sensor??
Are the radiator fans working properly?
 

·
Registered
Joined
·
27 Posts
Discussion Starter #20
Sounds to me like the mixture is too rich to allow the engine to idle when the fuel system is operating in open loop. It will idle once it switches to closed loop (warm engine) because a lot of fuel is being trimmed away, weakening the mixture (negative trim figures). As I said earlier, no fuel trimming takes place in open loop.


A quick and easy test I would try is run the engine until it is able to idle, then set up your scan tool to monitor short term fuel trim.
Now take a pair of long nosed pliers and use them to clamp the hose between the inlet manifold and the purge control valve.
See if clamping that hose makes a significant difference to the fuel trim figures. If the fuel trim goes more positive when the hose is clamped you may have a leaking purge valve, which could explain the negative fuel trim.
I’ll definitely try that this weekend. I don’t think I’ve looked in that area before.
 
1 - 20 of 21 Posts
Top