My XLR is throwing two codes...PO171 and PO300

[oyealiz]

Any ideas on what the issue(s) could be? And what will need to be repaired?

The PO171 came first. No symptoms. Drove home and one more short run. Next time I started her, she's missing (running rough) and now has the PO300 code.

PO171 = fuel trim system lean bank 1

PO300= random misfire

 

[AL_Jazz]

On quick glance through the shop manual diagnostic procedures for both of those, (6-846 and 6-872) start with looking for broken, cracked, or loose vacuum hoses or intake. Quickest way to check for a vacuum leak is a can of starting fluid (with a straw tube on the sprayer) and lightly spray around your intake and vacuum hoses while the engine is running. If you notice an increase in RPM, you have found your leak...if that is the issue. Lean condition could also be low fuel rail pressure or an injector issue. Just a place to start diagnosing...

 

[Cadillac Tech]

I would replace the #1 O2 sensor on that cylinder bank. I have seen a bad O2 sensor cause this condition. Best info I have without seeing the car.

 

[oyealiz]

Suggestion from another thread was to check the bolts on the intake manifold. Kevin checked that and said the intake manifold was about to fall off! He said that all the bolts were either not tightened correctly, or they vibrated loose. And, for the running rough, he thinks he accidentally unplugged the #8 coil when he put the cover back on after checking on the check engine light issue the first time.

Back up and running, yay! Now to get my exhaust. (And a warranty, yes?!?!?! )