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Car idles funny but doesn't throw codes


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eqrash
User

May 13, 2024, 8:38 PM

Post #1 of 10 (853 views)
  post locked   Car idles funny but doesn't throw codes  

2006 Hyundai Elantra
Engine size: 2.0L
mileage: ~312,000

I’ve checked just about everything I can think of, plugs are clean and right gap, o2s are new, idle air control valve is new, maf is reading fine, air filter is new, coolant is full and seems to cycle, temp sensor seems to read about what an infrared thermometer does… But it seems to idle rough and revs up and down when the car is sitting and idling for a while… It runs and drives fine if I give it a little gas when it idles low or poke the accelerator and release the idle will drop back to normal… But I can’t figure out why the computer keeps changing the timing advance… No codes are popping up, it just revs funny sometimes…

I don't think I ever messed with the timing belt position... I have been meaning to change the belt but could it have been tampered with? Could it be as simple as advancing the timing belt by a tooth? How do I check the timing belt on this vehicle?

I can't seem to post an image least I provide a link... This is what I'm getting on my little obdII scanner....




(This post was edited by Hammer Time on May 14, 2024, 3:22 AM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 14, 2024, 3:24 AM

Post #2 of 10 (836 views)
  post locked   Re: Car idles funny but doesn't throw codes  

I edited your post to show the pic here.

Have you checked mechanical basics like the compression?

Check that the intake snorkel doesn't have any tears or leaks.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



eqrash
User

May 14, 2024, 4:53 AM

Post #3 of 10 (827 views)
  post locked   Re: Car idles funny but doesn't throw codes  

I haven't actually stuck a guage on it recently to check the compression, I have recently, in the last couple of months, but the car has no loss of power so I'd assume it's fine. I can check a little later when I can make more noise.

As per there being a hole in the snorkel, I don't think there is, I've been around with some air intake cleaner looking for vacuum leaks recently as well, I can check again when I can make more noise, but I don't believe there is any rips or tears.

I do have a Haynes manual for the car and looked up how to check the timing on the timing belt, I've done a timing belt change on this make and model before so its really not something I wouldn't touch, I just don't remember tampering with it on this particular vehicle.


(This post was edited by eqrash on May 14, 2024, 5:00 AM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 14, 2024, 4:58 AM

Post #4 of 10 (825 views)
  post locked   Re: Car idles funny but doesn't throw codes  


Quote
but the car has no loss of power so I'd assume it's fine.


That would be a bad assumption with the miles you have.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



eqrash
User

May 14, 2024, 5:02 AM

Post #5 of 10 (822 views)
  post locked   Re: Car idles funny but doesn't throw codes  

I know it's old, I maintain and oil it regularly though, and it seems fine when driven, it's not driven like a race car.

But again, I will check later when I can make more noise, I have a gauge for that and will check it.


eqrash
User

May 14, 2024, 8:35 AM

Post #6 of 10 (812 views)
  post locked   Re: Car idles funny but doesn't throw codes  

Nope, not compression related... I tested each cylinder for roughly 10-15mins and each held right about the same I left it with... I did it by removing all the spark plug wires and plugs, and bumping the key to turn the engine, and they held at like 110,90,115, and 115... I really didn't see a change in the pressure except for not turning the key enough or not knowing what position in the crank cycle it was at, I just bumped the key a couple of times and let it sit...

I did a visual inspection of the snorkel without taking it off, and it looks fine, old and dusty, but I didn't see or feel any tears or rips while wiggling it around...

I'm going to check the timing on the timing belt, its a pain but on second thought I think I tried toying with it once years ago, and its never ran quite right since. I could have sworn I put it back where I found it but I had a bolt missing from my exhaust, a bad O2, a bad idle air control at one point, and one of my flex pipes on the exhaust needed a new flex pipe welded in at one point... I kind of haven't double checked it... (Yes I disconnected the battery when I welded on the rocker panels and the flex pipe.) I need to do the timing belt some day soon anyways, I'm going to take a peek...


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 14, 2024, 8:42 AM

Post #7 of 10 (811 views)
  post locked   Re: Car idles funny but doesn't throw codes  

You might not want to hear it but there is your problem. The compression is way too low.

The spec for this engine is 218PSI with a minimum of 145PSI.

You got your money's worth. It's time for a new motor.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



eqrash
User

May 14, 2024, 8:46 AM

Post #8 of 10 (808 views)
  post locked   Re: Car idles funny but doesn't throw codes  

How many cranks are needed to register that compression? I just bumped the key like 4 times... I didn't crank it for a long time...


eqrash
User

May 14, 2024, 9:29 AM

Post #9 of 10 (803 views)
  post locked   Re: Car idles funny but doesn't throw codes  

I'm still gonna check the timing... I think the guy that showed me how to do the belt said if it gets off by even a tooth it can lower the psi cuz it changes when the valves close and when the piston compresses the cylinder... If I need a motor I'll have to find a way to do the repair but I think you're telling some people wrong... when the cam shaft and crankshaft are out of sync it can cause a lower psi, its holding psi, but its starting to compress later in the revolution because the valve is open or closed too long or at the wrong time.

It looks like I need a new belt anyways, just trying to break the tensioner loose...


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 14, 2024, 10:08 AM

Post #10 of 10 (796 views)
  post locked   Re: Car idles funny but doesn't throw codes  

OK, you know better than I do. What do I know.

Timing belts don't move once installed. You have over 300K on that engine and it's time for it's funeral.

I'm closing this question now as you are unwilling to face reality.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







 
 
 






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