All at once yesterday, the car started idling very lumpy. While driving, she seemed fine though. Which was good, as I was on a short road trip. I had no CELs.

This morning however, just as I started driving back to work from the hotel, a slew of CELs / OBC codes hit at the same time.

P030X misfire codes for every cylinder except the number 1and 3.
P1316 code for excessive misfires and emissions
P0133 & 0153 for both upstream O2 sensors “Slow to Respond” (both sensors are only about 20,000 miles old)

Again, except at idle, the car seemed to be driving fine so I cleared the codes. Then I checked pending codes “while” I was driving.

P0171 & P0174 both banks lean. So I checked the FTs.

During cruise on level or downhill roads all the FTs were max’d out and steady. No fluctuations at all. Completely max’d out.
However, if I put even a little load on the engine, say while accelerating slightly uphill, the FTs immediately (and I really mean “immediately”) dropped to normal. This should rule out "supply" problems - pump, filter, MAF, etc.


I haven’t had a chance to pull the plugs yet (tonight), but I’ll bet they’re going to be sooty. Over the 150 mile trip, I averaged at least 1 MPG below where I should have: 23.3mpg @ 41 mph (I plot Avg MPG vs. Avg MPH for every tank of gas)

Like I said at the start: This situation hit all at once yesterday. The car has been running SWEET for many thousands of miles, so some “single” thing has happened to cause all these anomalies.

ECM? Throttle Position Sensor?

I should add: When I popped the bonnet briefly yesterday, there was a strange and noticeable noise coming from (or around) the supercharger. It almost sounded like sucking. That’s unlikely though, as both sides would have had to develop drastic (and equal) leaks simultaneously, and I just installed new intake gaskets & seals all the way from the TB to the heads last Spring. Could the SC itself be going? What the Hell does THAT sound like?! I just changed the SC oil about 30K miles ago. It's been running quiet and smooth.

I'll post again later with the spark plug results. But I'll take any guesses to the problem's cause in the meantime.

THANKS!

 

Sounds like an air leak to me, as the symptoms are worse under high vacuum. Are there vacuum lines on the throttle body you can check? I would pursue the source of that noise and see if it leads to a popped hose of some kind. Just a thought.

Best of luck, keep us posted.

 

Thanks FM. Yeh - classic vacuum leak scenario. I replaced all the seals & gaskets while chasing down a constant P0171, and found a broken EGR pipe. But the car ran fabulously despite the P0171. The onset of the current scenario was so abrupt and the effect on engine operation was so dramatic that I was thinking it could be something else. The "instant" FT recovery seemed odd, and the "Slow O2 Sensor Response" codes kinda mucked things up in my mind as well.

The one breather hose I could not visually check last night was the one from the right valve cover to the rear of the engine - where it plugs into the elbow. I'm heading for that connection first when the air duct comes off.

 

I'll tell you what - that propane test for vacuum leaks isn't worth SQUAT! Turns out the leak was from a huge tear in one of my brand new, 80 friggin' dollars a piece, supercharger boots. I put the propane right up against that area and none of the FTs even blinked. I finally found the leak by dangling a paper towel into the area. The leak was so bad that not only did it pull the paper towel toward it, it sucked the paper towel INTO THE DUCT! Thankfully, I saved the OEM boots, which were just fine, when I installed the new ones. As soon as the engine cools, I'll make the swap and report.

80 dollars a piece! Just shoot me.

 

Yup. That's got it. Friggin' boots. It took a long time for the idle FTs to come down, but they finally settled below 10. The running FTs were all over the place though. Sometimes the LTFTs were max'd positive while the STFTs were max'd negative and occasional the LTFTs settled for a while at around 5. No CEL. All is good. We'll see what she's like driving around town tomorrow.

At least I didn't have to rip the top of the engine apart. Given that all the other gaskets and seals I put in were "similarly new", I'm gonna be worrying for a while.

 

Was it actually running closed loop? With such a big leak, may well not have been. Trims are moot if not. (They're not valid.)

 

Hi JV8. I'm not sure I know how to tell if it was closed-loop. The engine was completely warm though. I did the test shortly after returning home from work, and the engine was running for quite a while during my search.


Now "this" is odd: My idle FTs are down to 8.4, but my higher rpm (2K) FTs spiked to "maximum" this morning (19.5 is as high as my reader will report LTFTs). And I threw a P0171, which hasn't appeared in many, many months since replacing the EGR pipe and fixing the brake booster fitting. (sigh). Guess I'll clean my MAF sensor (again) tonight.


I wonder if all those miles driven with the torn SC boot mucked-up my O2 sensors?

 

OBD tool like elm327 can tell you.

 

Thanks JV8. I've got a pretty good plug-in reader so I doubt if the ELM would tell me any different, but I have been considering installing one just for convenience.

Other than one P0171 and an RP the next morning, I've been CEL free, so I'm hoping that the O2 sensors and ECM are settling back to normal. Driving 150 miles with that torn boot probably messed up my baseline pretty badly. Cruise FTs are now around 6 and idle FTs are around 8. Not bad.