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.

 

Forgot the vehicle, in case you need it - 96 Elantra

 

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.....

 

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?

 

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.

 

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

 

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

 

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.

 

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.

 

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