Good news, my recent battery cable replacements seem to have worked fine so far. Bad news, while driving on the freeway back from Maine in cruise control at speed, the check engine light popped up and when checked in the Torque App, it revealed the codes P0174, P0171, P1111, indicating "powertrain system too lean [bank 1 and 2]". Since these didn't seem to be anything that would prevent getting home I continued, and later experienced some hesitation at freeway speeds while under load, that I assume was the car not being able to burn all the fuel properly if it is running too lean.

Questions: after looking into other people on the forum who've come across these codes, it seems they are related to either the intake manifold gaskets (upper and lower), vacuum leaks or brake booster hose. Anybody have any input on what they think they might be?

Many thanks in advance for your input.

 

There are many threads about them so do some reading

You'll need a tool for live data as per the threads.

 

I’m betting a vacuum leak. Search for several threads on that. I changed all parts for the major culprits and still had the leak. Mine turned out to be the small vacuum tube that attaches on top of air intake and connects other end to fuel pulse valve on the 3.0 engine

 

Ian, because you are getting the code on both banks, odds are, you are looking at an issue with the PCV hose. You don't mention the year or engine that you have. But, if you look at the front valve cover near the driver's headlight, you will see the PCV valve and you can follow the PCV hose back to the intake. If you have a smooth hose, definitely replace it. I bet you will find that on the underside of that hose it will be split. If you have the ribbed hose already, then I would be next checking the vacuum line that runs between the top of the intake and the brake booster. If you look near the brake booster, you will see a "football" shaped piece in the middle of the line. Rub it with your finger. Does it start to crumble as you rub it? If so, it is time to change it as that is most likely your cause of leak. Known failure item.

You can replace the IMT valves, but normally these will only cause a vacuum leak on one bank, not both. Having both vacuum codes come on at the same time would indicate that both IMT valve o-rings failed at the same time. Not impossible, but, not likely either. But, these are also cheap and easy to replace just to eliminate the normal sources.

If you still have a problem, the next place I would look is at the accordian piece just upstream of the throttlebody for a rip. Because you got both codes at the same time, the problem tends to be upstream of where the air flow splits. This pretty much leaves it upstream of the throttlebody unless it is a pretty significant leak.

Your other option (smokers love this one) is to pull out a cigar and light it up and with the engine running, gently blow the smoke into the engine bay and watch the smoke waft through the engine bay. Where you see the smoke make a sudden change in direction points you to where the vacuum leak is. The big thing is you should tend to do this with the motor cold and ensure that the dash heat-A/C is turned off. By doing these 2 things, it will help ensure the fans remain off, making tracking the smoke easier. If you have the fan running, they will tend to push the smoke around, making finding the vacuum leak more difficult. If you don't smoke, I am sure you have a friend that will smoke a nice cigar for you if you buy them one.