Wonky engine revving.

A couple days ago my LGT started revving up to 3k RPM (give or take 1k) while driving. RPM would drop back to normal if I blipped the throttle so I drove it home and parked it for the night.

The next morning I started it up and instantly it is holding around 3k RPM so I shut it off. I had a spare pedal and 5 min so I swapped it. No change.

At this point I reset the ECU and that has helped it not rev freely while driving and if I blip the throttle after startup it will go down to normal.

I have researched over the last 2 days and have come up with either a faulty 02 sensor or TPS. No DTC whatsoever and the car will drive normal now after startup.

Anyone have any sage advice before I change the 02 sensor? I have not experienced a bad 02 sensor without the corresponding check engine light.

I would try cleaning the throttle body first.

As stated, a log would give us more information. Good luck

Does it make any sense that I just started it with the 02 sensor unplugged and it started normally?

I figured if the throttle itself was sticking it would get stuck at a specific rpm insteadof the hunting type of behavior it is exhibiting.

I can log but cannot upload until the morning.

Wouldn't the throttle body need to be removed to clean properly? Doesn't that require removing the intake manifold?

You can pull the TB-Intercooler hose and spray TB cleaner and scrub away with a toothbrush without pulling the manifold. Shouldn't take more than 30mins.

Car running fine without O2 sensor leads me to believe an issue with closed-loop operation, which could very well be a failing O2 sensor (or failing MAF sensor, MAP sensor, ECT sensor, etc.). Doesn't sound throttle/DBW related to me.

Speed density so no MAF and MAP can't have 10k miles on it.

I'll give the throttle body a quick scrub for good measure.

Can't find an o2 sensor locally anyway.

Stupid Ford country.

Speed density so no MAF and MAP can't have 10k miles on it.

 

I'll give the throttle body a quick scrub for good measure.

 

Can't find an o2 sensor locally anyway.

 

Stupid Ford country.

That makes more sense. I wouldn't expect that sort of behavior without CELs or other major drivability issues on a MAF setup. I'm not too familiar with SD, but from my understanding the only inputs it relies on are manifold pressure, intake air temperature, and RPM. Which means sensor-wise, you could have a problem with MAP sensor, IAT sensor (which is part of the MAF unless you've changed that as well), and I believe crank position sensor.

Perhaps it's worth checking the contacts on the MAF sensor or wiggling the harness? They're known to become intermittent causing all sorts of fueling issues on MAF-based cars. If the IAT sensor contacts are intermittent, I could see that screwing things up on an SD tune.

Yeah the IAT is run into the MAF harness.

I have fiddled with the MAP and the IAT wiring. Based on the change when the o2 is unhooked I'm still leaning in that direction.

While my tuner seems to do a good job, he doesn't explain much (understandably) and the SD details were certainly not divulged. He makes the "kit" including IAT and wiring.

There really aren't any driveability issues after the ECU reset other than the revving at startup.

I'll try to log a pull on the way to the gym and upload in the morning.

For what it's worth, the 3krpm rev hang happened to me on a cold startup, once, this winter. I had the AF sensor fail within a month of that, but could be a coincidence. If you want to test it out, I have a known good spare that I pulled off my parts car.

Thank you for the offer, but I already ordered one online. After finding out nobody stocked them locally.

Not sure how helpful this abbreviated log will be, but I'll post anyway.

The difference between the target boost and actual boost is very odd to me.

Also the throttle position dipping below %100 shortly after the pull begins is interesting as I'm fairly certain I didn't lift until the end.

I could have sworn I had different parameters setup to log, but I guess not.

datalog16.1.csv

datalog17.csv

Update.

Upstream O2 has been changed for a couple weeks. (only had to remove the headers twice) :spin:

The car still revs to 2.5k rpm upon initial startup and revs between shifts constantly until at operating temp and sporadically after. It is most prevalent between 2nd and 3rd gear and when shifting into neutral and coming to a stop.

The difference between my boost target and actual boost remains the same as in the logs I posted. Fuel trims are better (all within 3%-7%) and I cannot find any leaks using the "block off the intake and blow into BPV hose" method. Air pressure holds for 5+ seconds and when I remove my thumb from the line I can hear the air escaping.

I'm at a loss and beginning to wonder if my AEM MAP sensor is bad. Are there any other values (other than boost target and boost) that I can compare to verify proper MAP functionality? I found MAP absolute pressure, but have no idea what that should read in comparison to everything else.

Thanks, un fortunately that doesn't make any of the values I'm seeing make any sense.

I cleaned the throttle body (on the car) a little more vigorously yesterday and the revving got worse.

I'm leaning towards replacing the throttle body (or at least the TPS) but I don't see how that could possibly be causing my difference between target boost and actual boost.

I've also unplugged and reseated both the throttle body plug and the APP plug. Neither showed any signs of corrosion.

Replaced throttle body with integrated tps with one I found for cheap along with the throttle body to intake manifold gasket.

No change in anything. Currently considering taking it to TiC instead of reloading the parts cannon.

Just took a look at the logs you posted earlier... no reading of the MAP sensor in any of them, and a bunch of parameters that aren't particularly helpful in diagnosing this stuff (TD, wastegate max, AVCS). In all honesty, depending how your tuner set everything up, your boost target mismatch doesn't mean much of anything. If your measured boost looks okay, that's all you need to worry about. The target boost parameter has other compensations applied before it's really used in the turbo dynamics. You'll notice that your boost error doesn't actually equal "Boost - Target Boost" precisely for this reason. Boost tuning is predominantly done with the wastegate duty tables.

Can you post some logs with your MAP sensor readings chosen as a parameter?

Just took a look at the logs you posted earlier... no reading of the MAP sensor in any of them, and a bunch of parameters that aren't particularly helpful in diagnosing this stuff (TD, wastegate max, AVCS). In all honesty, depending how your tuner set everything up, your boost target mismatch doesn't mean much of anything. If your measured boost looks okay, that's all you need to worry about. The target boost parameter has other compensations applied before it's really used in the turbo dynamics. You'll notice that your boost error doesn't actually equal "Boost - Target Boost" precisely for this reason. Boost tuning is predominantly done with the wastegate duty tables.

 

Can you post some logs with your MAP sensor readings chosen as a parameter?

Yeah I can take a couple logs. The boost vs target boost was just a new thing I noticed that had never looked that way before all this.

The log will likely not be a normal WOT 3rd gear pull as I don't feel comfortable driving the car far enough to my normal logging spots. The revving when the clutch is pressed in has reached 4k rpm a couple times and I'd rather not get too far from the house.

Would a log while idling be helpful at all?

The only MAP parameter I showed said MAF (MAP) and never changed from .96 g/s.

Unfortunately I doubt I'll be able to post the logs until Tuesday as I left my laptop at work Friday.

I'll see if I can download AP manager on my tablet.

Edit: No dice on the AP manager download.

For speed-density, MAF (MAP) is a calculated value of airflow based off the MAP sensor (pressure), IAT (temperature) and the RPM (volume), and it should be a directly correlated to your load, or in other words, a combination of your RPM and throttle position, as well as your boost. If that's not changing, then there's definitely a problem.

A useful paramater to log would be manifold absolute pressure (not sure what Cobb calls it, or if they even expose it for logging). That's a direct conversion from the MAP sensor. There may even be a MAP voltage parameter, but I'm not sure about that.

There is a manifold absolute pressure but no MAP voltage.

The MAF (MAP) parameter definitely didn't move from .96g/s in my trip around the block. A bad MAP sensor could also explain the new boost/target boost relationship.

Just hard to believe an AEM 3.5 bar MAP sensor would fail around 10k miles. I'll clean it again and inspect the wiring closely in the morning.

Just to clarify:

MAF = Manifold Air Flow. Can in theory be measured anywhere, but is on Subies and most other cars measured before throttle body (and turbo when it exists).

MAP = Manifold Air Pressure. (Has to be measured after throttle, and sensor might be on throttle body).

MAP + TPS + Engine RPM is one way to determine the amount of air that flows into the system, the MAF is another. That's why some engines lacks a MAF since the MAP+TPS+RPM is sufficient, but a MAF can improve the in data so later engines have a MAF.

It's also possible to get rid of the MAP if you have a MAF, but I don't know if there's any engine that has that configuration.

Here is a second gear pull (datalog19) with the MAF (MAP) parameter. Unfortunately I didn't include the "manifold absolute pressure" parameter. Note MAF (MAP) is a constant .96 the entire time.

I'll also be sending this to my tuner in hopes he can find a few minutes to take a look.

The other datalog20 is me attempting to catch the odd behavior when coasting to a stop with the clutch depressed. Note the up and down fluctuation of the RPMs 2/3 of the way down the log. That is with zero throttle input.

datalog19.csv

datalog20.csv