I Changed full synthetic engine oil, filter and
air filter 12/17, rotated tires. Drove a bit locally
without issue. On 12/20, it was raining, the car did not
accelerate properly when entering highway.
After about 20-30 miles/hr, pressing down the
pedal won’t accelerate further. When press
pedal all the way to the bottom, still not
acceleration and the engine speed is just
2000 to 3000 rpm. When depress the pedal
can feel the car choke a bit. On the way back
via local, couple times it did accelerate to
about 40-50 miles/hour, if I slowly and gently
press the pedal. The temperature looks
normal. Engine light is off, so are other lights.
The car just passed its 150k miles mark.
Any suggestions what could go wrong?
Transmission? Brake paddle stopper? Thank
you and Merry Christmas!
What makes this problem better or worse?
slowly and gently press the pedal seems help to accelerate
How long has your 2008 Hyundai Sonata had this problem?
RepairPal Certified shops can diagnose and repair your 2008 Hyundai Sonata. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Remove air filter and check for ANY foreign debris that may have entered the intake tube interfering with mass air flow sensor - causing poor acceleration - no check engine light.
Just a hunch since the air filter has been replaced recently.
Otherwise seek *hands-on* assistance from qualified personnel.
Good luck!
Also inspect that big air tube from air filter box to engine - there can be NO leaks at any point!
This often happens upon air filter replacement and may take a few trips to show up.
Just trying to concentrate on the obvious after resent services and offer best ‘online’ guess..
That’s all anyone can do without the vehicle present.
Hi Pushrod,
Thank you for your time and suggestions. I checked couple things last night and the car somehow become running normal again. I will describe the details so not miss anything. Even though it seems runs again I still like to figure out what was wrong and fix it, so it does not come back again.
I checked the code although no engine light. No code. When I turn the key to on position the hissing sound was like before, indicating the fuel pump works at least, and maybe normally.
Turned the key to start, and found that the battery was low, so the engine is cranking but wont start, even when I pedal on for about 10 seconds. This reminds me (I forgot to mention) that on 12/20 when it did not accelerate properly, the battery was also low at start, but the engine was able to start when pedal on for a few seconds, and I drove out without waiting for the battery to be charged. I used the jump starter and the car started right away. When the car starts from cold it always has some cyclic grinding sound for a few minutes around crankshaft and camshaft, that I was believing to be due to the interference at cold temperature. This time I opened the hood and try to see if there is anything abnormal in that region. The car was running for about couple minutes and the grinding sound diminished as in the past.
I then stopped the engine. The battery red pole has no build up. I checked the air filter counter part. No debris from the air filter to the engine as I can tell, although I can not see the air entrance to the engine. The pipe seems clean. I removed the air mass flow sensor, and it looks clean too.
I need to get a fuel pressure gauge to measure the fuel pressure, and plan to check the catalytic converter the same time when I jack up the car. So last night I turns on the engine again without the jumper, and it started right away. I drove it out and everything becomes normal… I tried accelerate to 60 miles/hr and there is no hesitation of acceleration.
So the battery is my culprit and here is my theory. On 12/20 I marginally started the car with a low battery and immediately went on the road. The battery was still low, while I turned on the head light, the AC heater & defrost to high power, and also the stereo. The battery was barely charged when the car hit high way. So when I pedal up to enter high way, the battery cannot provide the power to the fuel pump to get more gas to the engine. Today when I went to O'Reilly I will also ask the battery be checked out, and probably get a replacement battery if confirmed. I will update when back from the store.
The battery is confirmed bad. The alternator is good. Replaced the battery and it drives good. I will drive and see for a few days. Thank you for the help so far.
Also inspect that big air tube from air filter box to engine - there can be NO leaks at any point! This often happens upon air filter replacement and may take a few trips to show up. Just trying to concentrate on the obvious after resent services and offer best ‘online’ guess.. That’s all anyone can do without the vehicle present.
Hi Pushrod, Thank you for your time and suggestions. I checked couple things last night and the car somehow become running normal again. I will describe the details so not miss anything. Even though it seems runs again I still like to figure out what was wrong and fix it, so it does not come back again. I checked the code although no engine light. No code. When I turn the key to on position the hissing sound was like before, indicating the fuel pump works at least, and maybe normally. Turned the key to start, and found that the battery was low, so the engine is cranking but wont start, even when I pedal on for about 10 seconds. This reminds me (I forgot to mention) that on 12/20 when it did not accelerate properly, the battery was also low at start, but the engine was able to start when pedal on for a few seconds, and I drove out without waiting for the battery to be charged. I used the jump starter and the car started right away. When the car starts from cold it always has some cyclic grinding sound for a few minutes around crankshaft and camshaft, that I was believing to be due to the interference at cold temperature. This time I opened the hood and try to see if there is anything abnormal in that region. The car was running for about couple minutes and the grinding sound diminished as in the past. I then stopped the engine. The battery red pole has no build up. I checked the air filter counter part. No debris from the air filter to the engine as I can tell, although I can not see the air entrance to the engine. The pipe seems clean. I removed the air mass flow sensor, and it looks clean too. I need to get a fuel pressure gauge to measure the fuel pressure, and plan to check the catalytic converter the same time when I jack up the car. So last night I turns on the engine again without the jumper, and it started right away. I drove it out and everything becomes normal… I tried accelerate to 60 miles/hr and there is no hesitation of acceleration. So the battery is my culprit and here is my theory. On 12/20 I marginally started the car with a low battery and immediately went on the road. The battery was still low, while I turned on the head light, the AC heater & defrost to high power, and also the stereo. The battery was barely charged when the car hit high way. So when I pedal up to enter high way, the battery cannot provide the power to the fuel pump to get more gas to the engine. Today when I went to O'Reilly I will also ask the battery be checked out, and probably get a replacement battery if confirmed. I will update when back from the store.
Have alternator output voltage tested as well - can be done in conjunction with battery testing.
The battery is confirmed bad. The alternator is good. Replaced the battery and it drives good. I will drive and see for a few days. Thank you for the help so far.