I've been running 5w-20 PU in my car since I've bought it. It was normally available at the local Walmarts, but it became unavailable. (I can do site to store now, but at the time that option wasn't available on their site for PU.) Anyway, I figured I could run Supertech 5w-20 synthetic for one interval until I could get a hold of PU again and not miss a beat. Also, I figured it might be an opportunity to find a hidden gem. Well, since I've put the stuff in my car, I notice that sometimes my car idles a bit "hard" and the idle will fluctuate. It has settled down some as I've driven it more, but it's still not like it was prior to the fill. Also, I noticed that the engine isn't as quiet as it was with the PU. Moving forward, I'll be going with QSUD or PP when I can't find PU since it was factory filled with Quaker State. I figured I'd experiment this one time. My question here is has anyone ever experienced something like this? I read reviews on Walmart's website for the ST synthetic oils and I saw another review that mentioned the same characteristics. I've always had a great deal of appreciation for the conventional and high mileage ST motor oils, but I'm feeling like I need to dump this stuff out as soon as possible since I'm not totally satisfied with it. I wish I could get my money back for this oil and get reimbursed for my OEM filter, but I don't think there's a way that can happen. Anyway, what are your thoughts?