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Hi, i have a 2004 sonata that i just got three days ago from my brother through a trade. car has 188xxx miles with an automatic transmission and the 2.7l v6. i've read around but havent found my situation yet but i have found some situations that are similar. the car has three codes, one for o2 sensor bank one sensor one, one for coolant temp sensor voltage, and one for something else that i am having trouble remembering. i'll get it scanned again and update this. the engine light comes on and off and rarely stays on.

from time to time the engine will surge, sometimes as high as 2500-3000 rpm. if i tap the throttle then it will drop back down for a few seconds at the most and then go right back up. sometimes it will lower the rpms on its own with no assistance. this happens while in park, neutral, and in gear but i havent found any patterns in this symptom to be able to say that its anything but random. this is mainly a problem when i'm at a light or stop sign trying to hold the car back with the brakes or if i pull up to a light with someone in front of me and this starts causing the car to try to jump forward. this problem will happen regardless of if the engine light is on or off.

if i turn the car off when it is doing this then i have to wait a few minutes before i can get it to start again. it will crank and will do so in what sounds to me to be in a healthy manner but it wont start or even give any hint that its trying to do anything but crank. at the same time that this started i had caught a bit of a fuel smell that lingers for a bit but goes away. i cant find any leaks or vacuum leaks with the old trick involving spraying starting fluid on the hoses and intake parts and listening for the idle to change. i did this test because i can hear what sounds like a sucking of air coming from around the throttle body. i have unplugged the maf sensor and have seen no change with the problem. i am currently looking into the idle air control valve and engine coolant temp sensor hoping that these things fix the issue but i'm also wanting to know if there is anything else that i havent looked into? ive read that the tps can cause this so it will be getting tested very soon as well.

This car has an aftermarket remote start system on it and i have been looking into if this could have anything to do with my issues. if i think of anything else then i'll will update this and i appreciate anyone taking the time to read this. take care!
 

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the car has three codes...one for coolant temp sensor voltage...from time to time the engine will surge
Engine idle speed is adjusted based on the Engine Coolant Temperature. If you have a fault with the coolant temp sensor circuit (P0118?) that could be the cause of the engine speed surging. It could also be the cause of your other symptoms too since the ECM will enrich the mixture in response to a high ECT signal voltage (low temperature). The enriched mixture could cause your O2 sensor codes and could cause too much fuel to be injected to allow the engine to start when it's hot.
 

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high idle, try unplugging the TPS while in park, don't drive it like this, but see if the RPM drops when you do. also mine has the same air sucking noise at the throttle body. for the longest time I thought I had a leak but after trying to starter fluid method a boat load of times I figured it was just the IAC just moving air but not leaking. how long does your engine take to get to temp? I ask because if you have restriction In your cooling system the coolant temp sensor may not be getting an accurate reading. good luck
 

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So it takes about ten minutes minimum to get to operating temperature when allowed to sit and idle. This seems like a little long to me so I'm going to go ahead and throw a new thermostat in it while I'm tearing into everything. I picked up the ects since I'm throwing a code for it and I've had a car before whose idle was crazy because of one. I unplugged the idle air control valve while the car was acting up and it immediately went to normal. Idled well until I plugged it back in.

I'm going to say my problem was a combination of a bad ects and a bad idle air control valve. I appreciate the info everyone. Take care.
 
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