Hey guys,

I'm hoping you can help with a modern car idle and fuel mileage issue. I have a 2011 Town and Country van with 3.8 v6. We bought it with a little over 90K miles and it currently have a little over 120K miles. Within the last couple of months, my wife it is shuddering at idle. It smooths out upon acceleration, but in general has less power than previously and mileage has dropped from the high teens to around 12. There are no codes. Looking at the rpm with my cheapy code reader, it was jumping about 100 rpm on average at idle with the a/c on. Also, the spark advance was jumping a few points. When I idled it up and held at a steady throttle pressure, the idle held steady and only jumped a few rpm. the spark advance jumped .5.

I'm betting that it needs plugs and general tune-up. I'm checking here to see if it could be anything else based on you guys experience. Thanks in advance!

Plugs will do that. I would also check the vacuum lines, seen a few with broken lines or ends falling apart. IAC will also cause idle issues.

How much data can you see with your tool? Short and long term fuel trim numbers at idle and 2000 rpm would be helpful.

Thanks, guys. I'll check the vacuum lines and see if the tool will read fuel trim numbers.

If I’m reading this correctly, at idle:
Shrtft1 is jumping between - 2.3 and 5.5
Shrtft2 is .8 to 2.3

Longft1is 3.9
Longft2 is 5.5

At 2000 rpm
Shrtft1 is jumping 0.8 to 3.9
Shrtft2 is 0.8 to 4.7

Longft1 is 3.9
Longft2 is 3.9