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Old 04-12-2013, 12:11 PM   #1 (permalink)
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Default 2003 Elantra GT - Erratic Idle, C3 Misfire

Hello all,
First time using this forum, hope I can find some help.

I'll start by saying my Elantra (~180k miles) has had a C3 misfire for as long as i've owned it (2 years or so). Gas mileage is good and it runs fine so i never looked too far into it. It may be unrelated but just worth mentioning.

Recently it started idling erratically... 1.5-3k oscillation. I took it in for inspection the other day (cleared the check engine light beforehand, i know, im a skeeze) and the check engine light came on while it was there... told me i needed to replace the Idle Air Control valve. So I did. didn't make any difference in the idle issue... it revs consistently between 1.5-3k rpm. I think this erratic idling causes the C3 misfire.

Of course, if I unplug the IAC, the thing runs much better. The idle is still high (1.5k), but is steady. Problem here is if i leave the IAC unplugged, it gives another check engine light indicating the IAC is unplugged, the computer not receiving the return signal.

This is where it gets strange. I got a great idea... leave the NEW IAC bolted onto my engine, but plug the old IAC in and just let it hang out under the hood. This way the computer would get the return signal from "an" IAC, be satisfied, and not return a check engine light. Well, that much worked, but surprisingly, the engine STILL revved erratically even though the IAC that was plugged in did not have ANYTHING to do with the engine!...

So all i've gathered is that if the IAC leads are plugged into anything (umm i tried plugging them into 20ohm resistors, same deal), the engine idles erratically. How could this be? Do I have another sensor that is screwing with me?

This is a hard one to explain so if i've left anything unclear just ask.
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Old 04-12-2013, 06:20 PM   #2 (permalink)
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Sounds like another intake leak, or maybe the MAF is hosed up.
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Old 04-12-2013, 07:29 PM   #3 (permalink)
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Did you have a 0507 code ?

Replaced the IAC and 0507 still come back ??

And we have a 0303 misfire code ???

Be a whle lot better if you include the code recovered, what you did to repair code, the result of repair, and the return of any code..
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Old 04-12-2013, 07:43 PM   #4 (permalink)
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Quote:
Originally Posted by stevepamboukes View Post
Hello all,
First time using this forum, hope I can find some help.

I'll start by saying my Elantra (~180k miles) has had a C3 misfire for as long as i've owned it (2 years or so). Gas mileage is good and it runs fine so i never looked too far into it. It may be unrelated but just worth mentioning.
Repair the misfire, good way to kill catalyst, if it hasnt started long ago..

Recently it started idling erratically... 1.5-3k oscillation. I took it in for inspection the other day (cleared the check engine light beforehand, i know, im a skeeze) and the check engine light came on while it was there... told me i needed to replace the Idle Air Control valve. So I did. didn't make any difference in the idle issue... it revs consistently between 1.5-3k rpm.

I think this erratic idling causes the C3 misfire.
NO, Intake chanber full of air feeding all 4 cylinder will not select a single cylinder for a misfire..

Of course, if I unplug the IAC, the thing runs much better. The idle is still high (1.5k), but is steady.
Yes... idle stuck with rotor fixed in place

Problem here is if i leave the IAC unplugged, it gives another check engine light indicating the IAC is unplugged, the computer not receiving the return signal.
PCM see open circuit on the motor circuit
#3 misfire is most likely a broken intake gasket.. sharp ear may pick up vacuum hiss,, squirt bottle of water will make noise as water sucked in broken gasket,, carb spary really show vacuum leak when sucked into cylinder.

The idle,, take a pair of long needle nose plier and pinch the evap hose between purge control valve and steel line that take off under the car.. possible purge valve not seated closed and leak enough vacuum to jack the idle, then PCM go wild trying to control idle with IAC (0507 - Idle higher than expected)
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Old 04-13-2013, 02:31 AM   #5 (permalink)
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Old 04-23-2013, 05:01 PM   #6 (permalink)
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Quote:
Originally Posted by stevepamboukes View Post
Hello all,
First time using this forum, hope I can find some help.

I'll start by saying my Elantra (~180k miles) has had a C3 misfire for as long as i've owned it (2 years or so). Gas mileage is good and it runs fine so i never looked too far into it. It may be unrelated but just worth mentioning.

Recently it started idling erratically... 1.5-3k oscillation. I took it in for inspection the other day (cleared the check engine light beforehand, i know, im a skeeze) and the check engine light came on while it was there... told me i needed to replace the Idle Air Control valve. So I did. didn't make any difference in the idle issue... it revs consistently between 1.5-3k rpm. I think this erratic idling causes the C3 misfire.

Of course, if I unplug the IAC, the thing runs much better. The idle is still high (1.5k), but is steady. Problem here is if i leave the IAC unplugged, it gives another check engine light indicating the IAC is unplugged, the computer not receiving the return signal.

This is where it gets strange. I got a great idea... leave the NEW IAC bolted onto my engine, but plug the old IAC in and just let it hang out under the hood. This way the computer would get the return signal from "an" IAC, be satisfied, and not return a check engine light. Well, that much worked, but surprisingly, the engine STILL revved erratically even though the IAC that was plugged in did not have ANYTHING to do with the engine!...

So all i've gathered is that if the IAC leads are plugged into anything (umm i tried plugging them into 20ohm resistors, same deal), the engine idles erratically. How could this be? Do I have another sensor that is screwing with me?

This is a hard one to explain so if i've left anything unclear just ask.
I had this happen in park only and had to replace the switch on the transaxle that sent signals to tell what gear it was in. If I put it in neutral or a gear it settled right down.
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