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Discussion Starter · #1 ·
Okay I just registered here today, as I do with any vehicle I purchase or own. I join the forums and share my knowledge and gain knowledge as well.

Anyways, bought a 2002 Sonata 2.4 with 135k, power windows all working, sun roof working, lights working, no burn marks (was a smokers car though) a few dents and scratches (Il be posting pics of the car here shortly).

The owner said he ran the car low on gas til there was none left and had to replace the fuel filter, this was two days before i was scheduled to purchase it. He replaced the filter and called me saying the car was not idling in gear ( it was previously not idling in park or neutral before the filter install ), then he calls back saying he got it working.

Shows up, cars running like a champ, quiet as ****, everything worked great. I pay him, end of deal.

First day I decided to install a after market stereo so I could have an Aux port. After blowing a couple fuses by accident ( cluster, ecu, radio, clock) I replaced them all with fresh ones and finished the install.

Now comes the problem...

I went to start the car up and it wouldn't start, so after maybe 4 attempts i gave it gas and it started. The idle went down so it wasn't holding it at 800 rpm or whatever it is.. i figured **** i forgot to reset the ecu so maybe the air fuel mixture is way off. My scion tc would turn off if you didn't let it idle for 15 minutes after resetting the ecu... soo I pop the hood, to my amazement the MAF sensor is disconnected...

I checked under the hood prior to buying the car and didnt notice this, dont know why!.. so i pop it back in, disconnect the battery neg for 5 min, press brake pedal, reconnect negative and go to start but it wont even hold idle. it turns off every time.

NOW it said on some Hyundai post to get in and immediately drive the car, i can do this and when i do it and then park the car idles fine and if you turn it off, it cranks back up with ease and runs perfect . but i have yet to drive it for 30 minutes as it said to do... maybe only 5-10 but still shouldn't that be enough for the ecu to learn the air to fuel ratio or is this another problem?

maybe the maf is dirty? haven't been able to check cause i don't have the torx bit.

Any input from you guys is GREATLY appreciated :D
feel free to ask any questions
 

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Or, try this get the engine fully warmed up to "closed loop" (learning ) mode, then remove the battery cables touch them together, then step on the brake to make sure everything is discharged, then replace cables, and let it idle for a few minutes, then just drive it in the style you normally do, this should do it!
 

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Discussion Starter · #6 ·
is the motor suppose to run rough after you reset the ecu ? Im not able to drive the car but I did the reset and when the motors cold I have to give it throttle for it to start, then hold on the throttle around 2.5k til it gets warmed up, then Im able to let off and it idles PERFECT.

Does anyone know the cause of this ?
 

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It is not uncommon for an engine to run a little rougher just after resetting the ecu, but this should only take a brief time for it to reestablish proper setting and then run smooth if that is the only fault.

But based on original post, it was marginally running properly when you bought it. Not knowing how to believe (from my perceptions) the former owner and what was done in maintenance in the car's history, you are caught in the middle of of the unknown in what needs to be done to get car running to your daily satisfaction.

If it was my car, I would clean the intake system, which would include the MAF sensor, throttle body, idle air control system, throttle position sensor, and PVC valve. I might even clean the EGR valve just to know it was not full of ****. Then see if it runs and idles correctly. If it seems good then, I would run it for about an hour to burn any residual cleaner from the system, then change the spark plugs and know that all should be good for some time.

The things I listed above are very common causes of poorly running, idling, and accelerating, either individually or collectively. SeaFoam Deep Creep cleaner and Electrical Contact cleaner and a couple hours of time should do the job - pretty cheap. Of course I can't guarantee that solves all your problems but it very well may, and is a cheap and good place to start eliminating common problem areas. And of course you learn a lot more about your car.

edit: Forgot to mention - look for any vacuum leaks, say an aged hose splitting at it mount or actually split anywhere along its length, or even detached. Look first about the throttle body assembly, and at the fuel pressure regulator. Car is old enough original tubing is definitely aging out.
 
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