Okay, this may be a little long, but I really could use some help.
My brother-in-law just gave us his 2000 Hyundai Tiburon. It had been sitting about 2.5 years as he had major problems with it and since he didn't have everything done at a Hyundai dealer, the warranty is void.
They had about $4000.00 worth of work done on it at a Hyundai Dealership here in St. Louis area and they still could not figure it out. When he had it, the check engine light was on and the car did not run right and would stall or just die and that's why the car was just sitting for so long and why the spent so much trying to get it going.
When we got the car, we replaced thebattery and tires and got is going. It was running fine, but then the check engine light came on. We took it to Auto Zone to have the code read and it stated (don't remember exact codes) random misfire, misfire with cylinder 2, misfire with cylinder 3 and misfire with cylinder 4. We replaced the plugs and wires, but didn't have the code cleared. Well, I was driving it for about 2 months back and forth to work (100 miles round trip) and got 32-35 miles per gallon gas mileage. Well, we have to have emissions test hereand when I took it in, they put it on the diagnostic machine and stated they couldn't pass it because of the check engine light and the codes coming off. We talked to another non-Hyundai mechanic who stated to have the code cleared and drive the car. Well, we had the code cleared on Thursday and it came right back on. We have taken it to the mechanic I last talked to to see if they can figure it out...but I thought I would ask for any suggestions of what might be going on. To us, if the car was misfireing, it wouldn't run very well and wouldn't get such great gas mileage.
Any ideas?

 

Is the code still a misfire code? Sometimes you can get a misfire and the car still runs okay. I tend to agree that there isn't anything wrong with the car if it runs well and gets good mileage, but if the code is still there I would guess one of the sensors is bad. Let me take a look at WebTech and see what it says. You can get your own logon to Hyundai's WebTech for free at http://www.hmaservice.comand read through the diagnostic charts. If you're going to try to do this yourself I suggest getting familiar with WebTech. I wrote instructions on registering and using the site. The instructions are at http://www.dfwhyundais.com/diy/DIY-WebTechGuide.html.

 

I looked and didn't see anything useful... except.... it says that the CEL comes back on until you have 40 warmup cycles (from cold engine to warm engine) with the condition that caused the CEL being cleared. So if you haven't driven the car 40 times from cold to hot since the spark plugs were replaced, you may have to drive it some more for the code to go away....

 

You stated that if the car is running fine and getting good gas mileage that it may be a sensor. Do you mean a sensor for the check engine light or what kind of sensor?
I have not driven 40 times since I had the code cleared, but I have driven it a LOT more than 40 times since the plugs and wires were changed, does it make a difference?
Thank you for your help!

 

If the plugs and wires cleared up the issue, I think it would have gone out by itself... there are several sensors that control the fuel and spark of the car; one of those could be giving the bad reading that's causing the CEL. Unfortunately I'm not a mechanic; I get most of my information from other forums and WebTech.

 

Hmm... i'm sitting here thinking and i'm at a loss as to why its still throwing a misfire code even though its running fine.
Exactly what codes is it throwing (P-----)?

What plugs did you put in and what wires?
Auto Part store aftermarkets or Hyundai wires?

 

both, aftermarket and stock plugs and wire have been used. the ecu has been replaced and about 4k worth of work was done by a hyundai delaer and they could not figure out what was wrong.

 

Has the coil pack been replaced?
Thats the only thing I can think of is maybe a weak coil pack.