Others, I'm sure, will chime in, but I chased a similar problem. There seems to be multiple possibilities for this issue.
If you have access to a scanner, I would check to see if you're getting any codes. I was getting the P0123 for TPS high voltage (I think). Plus the screwy numbers coming out of the live scanning pushed me to the TPS conclusion.
Hope this helps.
Thanks for that.
I found a device I purchased in the past from Innovate Technology. There's an app for your iPhone that's free, but the tuner part that plugs into the OBDC port is a purchase.
I plugged it in (thanks to those who steered me in the proper direction to find the port) and it connects via WiFi to my iPhone. There are numerous cool features with this device. I've captured some screens for you to see:
Here is the trouble code section (no problems reported):
Fuel economy section below:
Finally, a graph from a run I took up the street in my neighborhood. Just testing this out. It's full of great information:
I didn't know this would work on my SLK32 AMG... but it works great. I believe the cost was only $145 when I purchased. Again, the app is free for the iPhone. I don't know if they have an app for Android phones or not.
The device works by WiFi. Just don't leave it plugged in and forget about it. I ran down the battery on a Mazda RX8 be leaving it plugged in and forgetting about it. I couldn't figure out why the battery kept running down. I'd forgotten all about the device, tucked up under the dash...
Anyway, if anyone wants a slick, inexpensive system for checking out many things on their car, this will do it. The website is tuneyourengine.com
. I have the OT-2 Scan Tool, which is shown above in screen captures.
Hope someone finds this info helpful. I've even cleared engine trouble codes using just this device. Very helpful in that respect.