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Discussion Starter · #1 ·
Hey guys. I just joined the board but I've been a looker for over 2 years. We purchased our first Hyundai Elantra GLS (base no ABS) back in April of 11 and have loved the car ever since. We have 129,600 miles as I pulled into the garage. We have used it for gas savings and it has been worth the initial cost x10. Until recently.... :)

Back in October I need to replace the struts and the down stream catalytic converter. We reused the old o2 sensor and the code went away. Since then we have found out that the wheels need to be replaced due to being bent. There was a lot of shaking going on upfront which is why we replaced the struts to begin with.

Now flash forward to the last couple of weeks. We've noticed issues with the car going haywire for no real reason.

- the car will have issues shifting from 3-4
- the car will shut itself off after idling for 3-5 min with the heater on
- the car will try to start and rev to approx 1k rpms then die

After the car dies it might take 2-10 different tries to get the car back operational. I don't believe the transmission is going out however I do need to either flush or do a partial flush with new fluid. The car throws a code when it stalls or bucks moving from 3-4 but will not retain the code for viewing.

Today I replaced the input and output sensors after reading many of the experiences had by Elantra owners. After driving the car 2-3 mi I shut it off and started it back up. I had shifting problems, issues with idle and the car stalling. After I finally got the car started and running I took it for a drive to a local larger city 10-12 mi) and had issues with the car bucking while on the off ramp but never had an issue since. At the parts store I turned the car on and off 15+ times, and never had an issue.

I'm getting frustrated with this as it is what we drive daily and with the temps not higher than 20 here in the Midwest I can't risk hauling out 2 year old in the car.

Possible options that come to mind:
- downstream o2 sensor is bad?!?!?!
- transmission low on fluid? (Doesn't explain why it will stall even in park)
- sensor replacement but which one?
- transmission going out?!?!?!

Any and all help and advice will be greatly appreciated.

Thanks,
Nate
 

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Throttle position sensor is the first thing I can think of. I cant remember the coloring or part number, but there was an issue that would cause stalling, amongst other driveability concerns.
 

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Discussion Starter · #3 ·
Thanks, I'll add TPS to my list.

Do you think this would cause transmission issues?

We have not experienced any issues with the car until we replaced the struts and found out the wheels were bent.
 

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Discussion Starter · #4 ·
Could this be related to the charcoal canister?

I find it odd that I can drive the car ok sometimes but not all the time. Fuel filter?

Idle air control valve?
 

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Could this be related to the charcoal canister?
no

I find it odd that I can drive the car ok sometimes but not all the time. Fuel filter?
no

Idle air control valve?
without supporting trouble codes, i doubt it.

occam's razor suggests that these problems are related - provided that they presented at roughly the same time.

i think the big question is why would the car shut off only with the heater running? that doesn't seem to make sense to me....the heater is only an extra heat exchanger on the coolant system. is the car overheating? an auto shutdown at idle *could* be a safety feature in the ECU to protect the engine from damage.

the high idle would suggest a rich mixture....

the shifting would seem unrelated....

its difficult to say at this point....you've got a good one. i enjoy trying to crack problems like this. start with some general checks. i'd like you to get a mechanic's stethoscope on the injectors to start with (see that they sound the same, sharp snap when firing), any ECU (check engine light) codes must be known. a code scanner is not necessarily expensive. also would like to know condition of trans fluid. pull dipstick out, put some of the fluid on your fingers. does it look cherry red or brown? does it smell burnt? does it feel gritty when rubbed between two fingers?

finally, start checking for intake leaks. trans shifting is based on the throttle position sensor and your RPMs. the poor man's test is idle the car and spray some start fluid around the hoses and intake (especially gasket area) and see if the RPM's change. it should increase and be quite obvious, but may be delayed by even 10 seconds.

this is after you check all those vacuum hoses for leaks and cracks of course.

at this point i need more info to solve this one....see what you can find.
 

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Discussion Starter · #6 ·
without supporting trouble codes, i doubt it.

occam's razor suggests that these problems are related - provided that they presented at roughly the same time.

i think the big question is why would the car shut off only with the heater running? that doesn't seem to make sense to me....the heater is only an extra heat exchanger on the coolant system. is the car overheating? an auto shutdown at idle *could* be a safety feature in the ECU to protect the engine from damage.

It has not overheated. All the coolant levels and everything else is in check. When at idle and it stalled it seems like the rpms just get lower and lower. The car idles around 500 rpm typically. Does that mean the timing might be off? I had a shop replace the timing belt, etc about 10-15k back since I wasn't sure if/when it had been done.

the high idle would suggest a rich mixture....

the shifting would seem unrelated....

its difficult to say at this point....you've got a good one. i enjoy trying to crack problems like this. start with some general checks. i'd like you to get a mechanic's stethoscope on the injectors to start with (see that they sound the same, sharp snap when firing), any ECU (check engine light) codes must be known. a code scanner is not necessarily expensive. also would like to know condition of trans fluid. pull dipstick out, put some of the fluid on your fingers. does it look cherry red or brown? does it smell burnt? does it feel gritty when rubbed between two fingers?

the tranny fluid is more of a brown color which is why I'm going to have the shop flush or partially flush the tranny with Hyundai sp-iii fluid. Since I've never had the check engine light stay on I can't get the code reader to provide me with any codes.

finally, start checking for intake leaks. trans shifting is based on the throttle position sensor and your RPMs. the poor man's test is idle the car and spray some start fluid around the hoses and intake (especially gasket area) and see if the RPM's change. it should increase and be quite obvious, but may be delayed by even 10 seconds.

i replaced the unstable manifold gasket earlier this year.

this is after you check all those vacuum hoses for leaks and cracks of course.

at this point i need more info to solve this one....see what you can find.

Thanks for all your help so far. I will try to keep you posted on what I find out. I really appreciate you guidance as I am dumbfounded and I don't want to pay a shop to troubleshoot this and rack up a major bill. I'm fully capable of fixing almost anything I just seem to hit a brick wall with everything I think it could be. This is my first Hyundai and non-American made car so I'm new to some of the intricacies surrounding their design.
 

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Discussion Starter · #7 ·
I actually went out and tried to drove the car again. The problem seems to present when the car is "cold" after it sits for a bit. Since its 20 degrees as a high for the day, this will be a long winter if we don't fix it soon.

When I drove it just now, the car went about a mile was under load going up a hill and the car missed/slipped when going up a slight incline with my foot on the throttle just slightly as to not downshift.

I turned it back around and headed home.

When I pulled in the driveway I shut off the car and went I start it again. The car would start for 2 seconds quickly idle down and then stall. I did it twice and stopped. Same circumstances as I experienced earlier this afternoon.
 

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You need to get it to a Oreillys etc for a scan of codes.

Just throwing parts not really a good idea. Lots if stuff can cause an engine miss.
 

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Discussion Starter · #9 ·
Already scanned it... No codes to be pulled.

The only thin electrical that I've remotely touched was the o2 downstream sensor.

I only replaced the input and output sensor for the transmission because when reviewing others similar problems with shifting, etc it really sounded like my same situation. Apparently not. The old input and output sensors are back in the car.
 

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sabta06 - we've been after these codes several times now and the OP has stated several times that there are none.

i'm wondering...being so closely related to the outside temperature....does temperature of the engine make any difference?

low and dropping idle is a strong indication of a vacuum leak somewhere. get looking under the hood and test as described above, i think that has to be eliminated as a possible issue. if no starter fluid, use WD-40. similar results. keep in mind, the gasket you replaced may be a botched job. don't throw any possibility aside until proven.

best course of action here is to fix this idling/stalling problem first and then see if that has anything to do with the transmission issue. don't throw in random parts and don't try to fix them both at the same time.
 

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Small intake manifold leak causes cyclinder misfire codes ; really big would also cause codes.
No codes is the weird part, makes it hard.
Have you checked the torque on the intake manifold studs; it is a very awkward job and the manifold is heavy; so I'm thinking like zero right now.
It's only an $8 part normally, but it is critical.
 

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New intake gasket normally. Spraying might help confirm it, cyclinder #2 is where the intake gasket broke on my 2001 and 2002 Elantra's.

Had idling problems and cyclinder misfire.
 

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Discussion Starter · #14 ·
Must be a common problem. I kept getting a code when i finally replaced the intake gasket for the same problem as you are describing.

I'll check for leaks again and update everyone as soon as I find something out.
 

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i'd still like to know if the car has trouble once engine is warmed up....have another thought.

intake air temp. sensor...wanted to do a bit of my own research to see what sensors the car has for intake before mentioning this (not completely familiar with this engine). my theory is when its cold the sensor may not be reading this temp change correctly, and cold air is more dense. therefore, more fuel is required. if its not adjusting correctly then the mixture is off, you're running lean and could cause all of these symptoms.

the intake needs to be checked as well.

do NOT start replacing sensors yet! this is actually why i don't put down all my ideas normally...want more info to confirm since people seem to get trigger happy with replacing parts. there's no need for that and if anything makes diagnosis harder.
 

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to sum up: there are several valid working theories here. testing and more info is needed to start whittling that down to one.

and yes it is VERY strange we don't have any ECU codes...almost starting to wonder faulty ECU but that is rare and goes to the bottom of the list of possibilities.
 

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Discussion Starter · #17 ·
I sprayed the intake with carb cleaner and the motor didn't hesitate.

I want to check the voltage of the TPS and see what it reads.

I did go back to the input and output sensors and I realized that the input sensors pigtail connector had a crack in it and the latch (that snap connects to the sensor) was broke. I didn't notice this yesterday however I did notice that the output connector was tougher to get of when compared to the input connector; leading me to believe this has been broke prior to my replacement of the sensors. I'm going to contact the dealer tomorrow to see if I can purchase one of these as it will need replaced regardless.

More to come...
 
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