Steering feels light footed and wants to turn back when holding on a curve road.

[kvcobra]

Hello all....

A Month a go, pick up a 99 Wstar for cheap with 185k miles. The previous owner has had it since 56k and have never change the Trans oil or done a tune up. The only thing he did was change the oil regularly. I have replace the spark plugs, flush/fill the trans fluid & ps fluid, and replace all four shocks with sensatrac. So far I have put about 3500 miles on it and she still runs great so far with around 20-21 mpg hwy.

The only naging problem although I could probably live with is this steering feeling. When sitting idle, I turn the steering a little bit left/right I can hear something like an air release pop or swish. When driving on interstate and doing a gradual curve, the steering tends to want to turn back which makes the van feels very light footed. I have just replace all four tires with new at the front and newer used at the rear but the wierd steering feeling is still there and my power steering had new syn fluid and do not whine like others reported. Help me diag this problem. If it will cost too much to fix, I may just forget it. Thanks.