98 I30 engine hesitation

[lishumo]

Dear everyone, I got my 98 I30 few month ago. There are 134000km on it. The car is great except one problem.

The problem is, when the car shifts into the OD (around 58km/h-60km/h), and I try to slightly step on the gas paddel to keep the speed, the engine starts hesitating. It is really noticeble when going uphill. It is like lacking lots of power. If I step in deeper, the gear shifts down and then the power will be too much. As soon as I let go the gas paddel, it shifts into the OD again, and same thing happens.

I have changed spark plug, air filter, fuel filter and put a bottle of injection cleaner, cleaned the throttle body valve, and checked no exhaust leak, and new castrol sythn oil, new oil filter, but same s*** happens. BTW, the SES is not on.

Is there anyone had the same problem before? or any ideas?

[lishumo]

I have been using the 91 gas since I got the car~, idle is good and smooth
Modified by lishumo at 12:56 PM 7/8/2009