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Ask Proud Hyundai Owner (Corey) Your Own ...
Proud Hyundai Owner (Corey)
Proud Hyundai Owner (Corey), ASE Master/Hyundai Master
Category: Car
Satisfied Customers: 225
Experience:  Working cars 18 years on Hyundais since 1998 acheived highest level of technician awards for Hyundai
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2002 sonata: idles rough..runs fine..idles fine..traffic

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have a 2002 sonata, idles rough after driving around a while. runs fine when you start up. when you stop for just a few seconds it idles fine, but if you get stuck at a long light or in traffic or just sit a while the idle gets rough. car has new plugs, wires coils, canaster purge valve, idle air control valve, fresh oil and filter and air filter. and i cleaned maf sensor. any ideas?   Its driving me nuts.

Hello, I would like to know how many miles you have on the vehicle.

There still a few possibilities of what could be causing the rough idle.

Proud Hyundai Owner (Corey) and 8 other Car Specialists are ready to help you
Customer: replied 8 years ago.
Reply to Proud Hyundai Owner (Corey)'s Post: Hi, thanks for answering. the car has 94000 miles on it. i got it at an auction a few months ago so i dont know the maintaince history. It is a really nice car and seems to run fine when you are driving it no chugs or hesitationshen you give it gas when you are moving, it seems smooth. Its just after you drive it a while when you stop for more then a few seconds or sit with it runnimg its idels rough the longer you keep it running the worse it gets especally after getting off the highway any ideas? already tried those other things i mentioned.

I have worked on Hyundais since 1998 and I have seen this problem caused by partially

fouled injector with a bad sray pattern, sticking valvesand EGR system, Tge ijector theory when car is cold start the engine needs a richer fuel mixture so the dribbling injector works fine but when the engine warms up it needs a very fine spray mist so a dribbling injector will caus the rough idle. Sticking valves happen usualy after the car heats up valve stem hangs in the guide causing a slow closure. The EGR valve can cause the same problem giving a rich mixture when cold it is ok but when hot runs realy rough.

Customer: replied 8 years ago.
Hi one more time. what is an egr valve, and can i fix or replace it myself? Also will a fuel injector cleaner from autozone help at all? I have few options because money is really tight right now and i cant aford to bring it to a service center to get it fixed. I bought the car for my daughter and want to make sure it is safe to drive. it dosnt stall out or anything when idling so is it safe? Hope you can get back to me one more time with your advice, so far sounds right on the money. no one can seem to figure out what the problem is. Thanks again.

I would like to know if you have had the car checked for any codes set by the onboard computer (ECM)Engine control module.I also would like to know if yes what the codes were.

Injector cleaner might help but that is a (might). Injector cleaner is an inexpensive tool but not always helpful if you have a badly fouled injector. I also would like you to make sure you hvae a good working PCV valve Positive Crackcase Ventalation Preferable a new one. the PCV valve is located on the valve cover and has a hose that has been know to suck in on itself creating a vacuum leak it should not be flat anywhere

I also wanted to know if the timing belt has been changed it was due at 60k


The term EGR valve is (Exhaust GAs Recirculation) Valve.
Hello I just rememberd an easy check at no cost to you. On the top of the throttle body there is a green striped hose for the EGR system. When the car is warmed up and running rough pull that green striped hose from the top of the throttle body, if you do this and the idle smooths out the EGR solenoid is sticking causing vacuum to be sent to the EGR valve making stay open when it should not be.
Customer: replied 8 years ago.
Hi again you have been very imformitive. wow so many things it could be i will definitly be accepting your advice after this last time i hope anyway, m not sure about the timing belt, there dosnt seem to be any vacume leake(i will check that hose tomorow. no service light are on but the was an old code for that canaster purge valve wich i replaced and did nothing. could the fuel pump cause the rough idle because the car seems to loose a little power after a while especelly going up a steep hill ( could be because its just a 4 cylinder? i dont have a clue, Thanks again.

Hello again, Yes it could be fuel pressure related but I can tell you that motor is not very strong especialy with the a/c on

Fuel pressure (psi)Vacuum hose disconnection(47-50) at curb idle
Vacuum hose connectionApprox (38) at curb idle

I would definatley check the green striped hose theory first. Don't forget get the car needs to be completely warmed up to where it is doing the rough idle and pull the green striped hose from the top of the throttle body. If the roughness clears up you will need to get a new EGR solinoid.

The reason I asked about the timing belt is because that motor is terrible about when the belt gets worn it will jump 1 tooth on a cam gear and cause rough idle but that idle is the way all the time.

Remember if this one breaks it will distroy that head.

Hello again I was wondering if you got anywhere on the problem yet.

I will check every day. Remember if you need anything just ask.

Customer: replied 8 years ago.
Hi was away for the holiday weekend, didnt get a chance to mess with the car yet. I will try the green striped wire test tommorow and let you know what happens, thanks for asking.
Hello I understand that will be no problem I will be here at least once a day to check.