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George H.
George H., Hyundai Technician
Category: Hyundai
Satisfied Customers: 18696
Experience:  Hyundai Gold certified, ASE Master tech 15+ years
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I have a 2004 Elantra. 1. About 4.5 weeks ago the check

Customer Question

I have a 2004 Elantra.
1. About 4.5 weeks ago the check engine light came on (Engine Code P1166).
2. About 3.5 weeks ago the symptoms started.
3. Symptoms: When I step on gas more than a little (about 1/4) the engine gets a throaty sound and no added power or acceleration. Difficulty climbing hills (revs high). Less often, the car idles roughly and has stalled a number of times in 2 weeks (usually after climbing a hill or stepping harder on the gas). Rough idle can be fixed by turning off car and restarting. Car can get up to interstate speeds slowly on flat ground.
4. 3.5 weeks ago found a nest that mice had made in air filter compartment. Cleaned out.
5. 3.5 weeks ago I checked spark plugs and cleaned throttle intake and the mass air flow sensor. No improvement. The plugs were clean. A little carbon deposit on one eroded plug. Replaced that plug. I have 3 other new plugs.
6. 3.5 weeks ago I more thoroughly cleaned the mass air flow sensor. Check engine light went off briefly but then came back on. At that point I replaced the mass air flow sensor. No improvement.
7. 2 weeks ago the check engine light was off for most of the day and the car drove more normally around town but I did not try much hill climbing. The check engine light did come back on at the end of the day.
8. The next day I replaced the spark plug wires.
9. 1.5 weeks ago I took the car to the garage and they replaced the catalytic converter saying it was plugged. I thought the problem was fixed but the same symptoms came back in the afternoon on the 2nd day I drove it. The check engine light was back on shortly after I drove it home.
Submitted: 2 years ago.
Category: Hyundai
Expert:  George H. replied 2 years ago.
Hello I will help you with your question,
It sounds like your exhaust is restricted. Likely the result of the catalytic converter getting melted and when they replaced it some of the debris was left in the muffler.
See if they will drop the back of the exhaust and run it to see if it will now rev freely.
Was the airfilter chewed through? If it was look through the air intake for any leftover debris and inspect the little wire on the Mass Air Sensor to see if there is something caught on it. If there is remove it with a fine brush.
Let me know what you find once you check those two items.
Thank you
Customer: replied 2 years ago.
No damage to the air filter. The garage replaced the manifold catalytic converter but not the mid-line one. They said the car was set-up for California emissions though I'm not in California.
Is there a reason why the problem is intermittent?
When it is acting up it gets worse after reving higher as in climbing a hill (severe power loss and idles too low to the point of nearly stalling).
I think it is worse when the engine is hot.
Re-starting the car seems to temporarily reset the problem.
Expert:  George H. replied 2 years ago.
OK, then the mice didn't get to the mass air sensor.
I suspect part of the old cat is rolling around in front of the back cat or maybe to the muffler and acts as a plug. When you restart the car then the piece falls forward and until it is pushed back by the exhaust it is free flowing. Easy enough to check by dropping the joint between the manifold cat and the flex pipe long enough to see if it revs up and sounds normal again. The roar you hear is the restriction.
Let me know what I can do to help you with this
Thank you