Rough idle/ hesitation when reving...
 

I have a 2001 hyundai tib with 130k miles. It idles kinda rough. Enough to make the steering wheel shake noticeably. When I press the gas pedal quickly then let off, the engine has a moment of hesitation. It drops down to about 200rpm for a split second and feels like its stalling, then climbs back up. I tapped the gas pedal repeatedly (and very lightly) and the engine started sputtering then stalled. Occasionally, it will get really weird, I can lay my foot on the pedal very lightly and it will sputter like its going to stall, but adding a little pressure gets it back on track. I've replaced the tps 2 times, cleaned the throttle body, replaced the intake manifold gasket, checked all vacuum lines, replaced the fuel pressure regulator on the fuel rail, changed the fuel filter, and still no fix. I'm thinking it could be a bad motor mount causing the vibration at idle, but is the hesitation normal? When I rev it up to about 2K, it runs smooth with an occasional vibration in the steering wheel. I'm considering the front 02 sensor? If the timing belt has skipped a tooth, it would be running right?

How are your plugs and wires? Clean air filter? Be sure the MAF was installed correctly and not backwards if you have a CAI.

I don't think a bad O2 sensor would cause any problems right (except for bad gas mileage)? My O2 sensor has a broken wire (one of the two wires is broken it looks like)...but I don't have any check engine light or codes and my car runs just fine and gets 30+ mpg.

I would check the IAC being the issue is only close to idle, It may be carboned up and the valve could be sticking.



But the tune up items stated (plugs/wires/filter) need to be checked aswell.



What does it idle at with you off the pedal?



Why do you think the timing belt is off a tooth? Recently changed?



Do you have any way to read vacuum or fuel trims?

Did you replace the TPS with new or used sensors?

I replaced the tps with a new one off of ebay. Maybe it's just cheap? haha



My MAF was replaced right after I got the car and I have stock intake setup. Sensor is facing the correct direction.



I recently did plugs, wires, and air filter.



As for the tooth off thing, when I bought the car I was told the head had been replaced. At first I wondered if they did something wrong, but I'm starting to think I would definitely know if it was off.



The car is fast and gets great gas mileage.....but I can't stand rough idle! haha



Could it be a motor mount? And maybe all of this split second hesitation stuff is normal and I'm just not used to feeling it?



BTW, the reason I mentioned the o2 sensor is the quick hesitation. If the first o2 adjusts fuel trim, and the o2 is delayed or inaccurate or all of the above, then the fuel trim is incorrect for a split second. Right?



I have an obdii scanner (I think it still works). I'll check on fuel trim at lunch or after work.

Probably the IAC for the hesitation, but I can't imagine that it'll cause the steering wheel to shake. That sounds like a motor mount as well unless it's just trying to stall out at speed, which would be rather odd. Both of those are common at this age. The IAC can usually be cleaned which would take only a few minutes and only cost a can of carb cleanser.

O2 sensor.

Had a breakthrough!



I took my car for a drive yesterday and everything seemed worse. So when I got home, I popped the hood and poked around a little. I tapped the tps and the idle went down. I pulled on the sensor a little and it displayed all of the symptoms I've had.



So I unplugged it. Idle went up then came down and ran perfect....now for the new problem.



I tried doing a "quick rev" to see if it hesitated like before. It did not, however, I do here a loud knocking noise coming from around the valve area. Its only when I punch the gas the let get very quickly. Its after the tb is closed if that helps any.



I can rev high and hold it and there is no knock or tap or anything but quick rev=knock:/



I recently learned a little about HLA's. If these are needing cleaned, would they contribute to this noise?

Buy a *new* TPS and your engine running should improve drastically.



Stick your head right over the engine, and see if your loud noise is coming from the idle air bypass valve or the engine itself. If it's the IAC it's due for a cleaning.



Good advice in general for a new-to-you car with a Beta engine with HLAs: If you have something besides an OEM Hyundai filter, a purolator pure one, the expensive K&N, or similar high quality filter, change your oil filter to one of those and top off the oil. If you have the cheapest FRAM on it, definitely change the oil filter. The HLA top end needs a lot more oil than a solid lifter top end, and cheap filters starve it of oil. If it's just clattering a little like 1-2 clicks and then goes quiet, I wouldn't sweat it too much.



At your next oil change, run a flush through the system IAW the directions on the bottle before changing the oil. If anything will clean them, that will. Then use a quality synthetic in the appropriate weight with an OEM filter and don't worry about the oiling system again.