P0303 Code Update

Plugs and wires have been in service for approx. 10,000 miles. Reversed plug 2 and 3, still getting P0303 code only. Replaced ignition coil, no help. Motor runs great off idle through the entire power band, (that's why
I don't think the plugs or wires are the problems). Gets same mpg's. Only have rough idle condition. Noticed lately that engine rpm will increase slightly then back down to rough idle. Any component you can think of that would cause that condition? Thanks for all the help.
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why
Only
that
Forgot the vehicle, in case you need it - 96 Elantra
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Mine is doing almost the exact same thing P0302. It doesn't feel like a misfire. At idle the rpms move between say 750 and 800.
Some things I have tried to correct.
replaced coil (used part) replaced plugs and wires (new) replaced acceration sensor (new) used injector cleaner 2x pcv (new) air filter (new)
Tried to change the fuel filter yesterday, but its on very tight and need new wrench to get it off. I believe it to be the original filter. Car has 134,000 miles.....
Craig wrote:

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Thanks tj, sorry to hear you're in the same boat with us. I guess P0302 means your #2 cylinder is misfiring. I put on a used coil just like you, replaced the plugs and wires. I got a troubleshooting flow chart from the Hyundai site (hmaservice.com), I checked the primary and secondary coil resistance like it said in the chart. Secondary resistance was low on the coil that's why I bought a used one. Used one had the exact same readings as the original. I didn't replace the fuel injector but the car runs strong off idle and runs strong so I can't imagine it being the injector. The worst thing about the flow chart is the very last item says verify ECM connector is secure, if ok replace ECM and verify codes do not appear. I'll keep in touch with you, if I come up with the fix I'll let you know and if you figure it out, please let me know.
P.S. Where is the fuel filter on this heap?

Reversed
no
(that's
increase
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Not sure on the 96 Elantras, but on the 97's it located right below the brake booster/master cylinder and believe me it is tight fit!!!!! Line wrenches come in real handy for this!
Rick

coil,
mpg's.
of
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Hello Craig,
I also downloaded flowchart from hmaservice. I have my doubts that the computer is bad. But if it is. I found a few on ebay for about $100. Mine behaves very strangly some days the light is off other days it blinks like crazy. The other day the light started blinking while driving at about 55. So I pulled over to check how it ran at idle. It seemed to be running fine, I revved it up a few times while light was blinking and it seemed exactly the same as if light was off.
Does your CEL turn on at idle or while driving?
Fuel filter. Well Mine is a 2000 but I think its in the same place on the 96. driver side near firewall. Bought a new one from autozone. About $16. Tried to change it on sunday. The bottom fuel line is on there really tight. I would recommend using a 14mm line wrench. Also the bottom nut on the filter itself is very small so getting a hold on this is difficult. I was going to try a strap wrench along with the 14mm line wrench. Will let you know how this goes this weekend as I gave up on sunday. Also you have to remove the rear seat to unplug the fuel pump before you do this. After that start the car until it stalls and then remove the negative battery cable also.
Also what kind of plugs did you use? I've heard a lot of bad comments about using bosch plugs in these cars.
Regards,
TJ
Craig wrote:

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Don't replace the ECM! The flowcharts are flawed. If I replaced the ECM every time the flow chart said to do so, there'd be about 200 more cars out there with improperly replaced ECMs.
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Have you done any injector testing? If problem is only at idle, I would suspect a mechanical problem.
Do a cylinder leak down test. You may have a burnt valve, worn valve guide, worn intake cam lobe. etc.

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Check for an intake manifold gasket leak. The key to this possibly being the issue is that it runs fine off idle. At idle, an intake manifold gasket leak is a significant amount of the air sucked into the cylinder. At higher rpm's, vacuum is low and the leak becomes insignificant.
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hyundaitech,
Thank you very much for the accurate advice. I sprayed the area around number 3 intake with starting fluid and the engine smoothed right out. I checked all the nuts and they were all tight. I noticed a discolored spot on the intake manifold and could detect a slight hissing sound so I put a few drops of oil between the intake and the head and it sucked it right up. I cleaned the area thoroughly and put a thin layer of high-temp silicone gasket maker, (cheap fix), on the leaking area. You were dead right on this one. Thank you very much for your accurate and expeditious diagnosis. You saved me a lot of time and trouble.
Thanks again, Craig

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