Sonata NF (2006-10) :: Intermittent Rough Idle Caused By Power Steering Sensor Switch

I've been experiencing an annoying intermittent condition on my '07 Sonata (Lambda V6). I wanted to share this in case any of you are experiencing intermittent rough idle complaints in your Sonata (4G) as well. I was finally able to get it into the dealership during the malfunction; in my case, the MIL never lit. Here are the symptoms: ONLY after being fully warmed up, when coming to a full stop, or using just idle speed to, for example, pull into a parking space, or inch up to a stoplight, I would experience a very rough idle (I could hear the engine sputtering with the window down), see the RPM gauge bouncing, and feel the vehicle going "putt-putt-putt" as it tried to keep running under what seemed to be a misfire or too much load. The problem occurred more noticeably with the A/C off but still did occur with it on as well. While exhibiting this problem, acceleration from a stop gave a slight hesitation as well, but once going faster than 1,000RPMs, the problem went away totally. I thought it must have been my imagination until one day, I pulled up in front of a glass window and could see the reflection of my car lurching forward as it struggled to keep idling. Getting it to the dealership while it was behaving badly was the hardest part.

Once I got there, I got a tech to ride with me and finally, after 3 visits to the dealership, someone else witnessed the problem. Up until now, I've been asking people, "Do you feel/hear that?" "Huh?" I digress... The tech immediately said he thought it was a power steering issue and he thought there was an upcoming bulletin on it. I was sure he was wrong, I was thinking it had to be the spark plugs, wires, MAF, or TPS.

After getting the part in for me (Power Steering Sensor Switch) they put it in today and my vehicle is just as new again. It was never a serious issue, but was rather embarrassing to try and show off my Sonata and have it stutter and sputter like that it idle.

This part is complete speculation; maybe a more knowledgeable person can jump in here and correct any logical errors: Apparently, there is a switch in the Power Steering Unit that detects highway speeds versus slower speeds. When vehicle speed is above a certain limit, the power steering pump is either turned off or "turned way down" (so people get the stiffer feel of the wheel at highway speeds). When the vehicle slows down to idle (to be detected by this switch), the vehicle expects the power steering pump will draw full power from the engine and needs to have a slightly higher idle speed to compensate for the load. My switch was malfunctioning; it was not registering to the ECM that the power steering pump was under load when it actually was; the vehicle then did not bump up the idle speed appropriately, and thus, the rough idle and hesitation.