TPS and low RPM stumble

My logged throttle position sits around 4% idling w/o my foot off the throttle, pretty sure that's normal. Does the low rpm/stumble occur after the car's fully warmed up and has been idling for a minute or 2, or did you notice it right after reflashing?

-Right after- an ECU reset/map reflash, my car exhibits wonky behavior when slightly moving throttle position above base idle before the car is fully warmed up. As I just start to touch the pedal the rpms dip into the 550-600 range and the car feels like it wants to stall. If I let it warm up (coolant temp > 168-169) then let it idle for a little bit, it completely sorts itself out and idle/low throttle behavior is nice and smooth. I'm almost positive it's not an idle trim issue as I have CL MAF scaling pretty well dialed in.

TA mentioned in another thread that some cars need adjustments to the low throttle/idle airflow tables. I've done a bit of logging right after a reset/reflash and after fully warmed up and behaving normally, compared them and made a few adjustments but the changes didn't appear to do anything. Car's behaved like this after reflashes since I bought it 3.5 yrs ago, so while annoying, i'm used to it. It behaves fine after it fully warms up the 1st time after a reset/flash.

The TPS should never read zero while the engine is running. Older fuel injected vehicles with drive-by-cable throttle bodies used a special solenoid called an IAC (idle air control) valve. In those applications, TPS would read zero at idle, as the idle airflow was entering the intake via different methods. On our cars, with there is no IAC with our drive-by-wire throttle bodies. Instead, the ECU simply applies voltage to the throttle body plate actuation motor. So, in short, having a TPS reading above zero is 100% normal in our applications. For example, my outback typically reads 5% idling, and 7% with the A/C pump engaged.

Are you on stock fueling? If so, and you're getting a weird stumble, go into detail about it. Also, make sure you're up to date on all the scheduled maintenance; plugs, intake manifold gaskets, air filter, MAF, etc.

Edit: Low RPM stumble, assuming the car is 100% mechanically sound, is usually a MAF or injector scaling issue in the tune. Since you're only stage 2 I'm assuming you're on stock fueling. Do you have an aftermarket intake?

My logged throttle position sits around 4% idling w/o my foot off the throttle, pretty sure that's normal. Does the low rpm/stumble occur after the car's fully warmed up and has been idling for a minute or 2, or did you notice it right after reflashing?

 

-Right after- an ECU reset/map reflash, my car exhibits wonky behavior when slightly moving throttle position above base idle before the car is fully warmed up. As I just start to touch the pedal the rpms dip into the 550-600 range and the car feels like it wants to stall. If I let it warm up (coolant temp > 168-169) then let it idle for a little bit, it completely sorts itself out and idle/low throttle behavior is nice and smooth. I'm almost positive it's not an idle trim issue as I have CL MAF scaling pretty well dialed in.

 

TA mentioned in another thread that some cars need adjustments to the low throttle/idle airflow tables. I've done a bit of logging right after a reset/reflash and after fully warmed up and behaving normally, compared them and made a few adjustments but the changes didn't appear to do anything. Car's behaved like this after reflashes since I bought it 3.5 yrs ago, so while annoying, i'm used to it. It behaves fine after it fully warms up the 1st time after a reset/flash.

Yes we've found this, can be tuned out.

-Brian

The TPS should never read zero while the engine is running. Older fuel injected vehicles with drive-by-cable throttle bodies used a special solenoid called an IAC (idle air control) valve. In those applications, TPS would read zero at idle, as the idle airflow was entering the intake via different methods. On our cars, with there is no IAC with our drive-by-wire throttle bodies. Instead, the ECU simply applies voltage to the throttle body plate actuation motor. So, in short, having a TPS reading above zero is 100% normal in our applications. For example, my outback typically reads 5% idling, and 7% with the A/C pump engaged.

 

Are you on stock fueling? If so, and you're getting a weird stumble, go into detail about it. Also, make sure you're up to date on all the scheduled maintenance; plugs, intake manifold gaskets, air filter, MAF, etc.

 

Edit: Low RPM stumble, assuming the car is 100% mechanically sound, is usually a MAF or injector scaling issue in the tune. Since you're only stage 2 I'm assuming you're on stock fueling. Do you have an aftermarket intake?

Thanks for all the info. Previous owner stated he had all the maintenance done on the car. By stock fueling I'm assuming you mean stock fuel pump and injectors? Yes. Only mods on the car are catless up pipe, catless down pipe, cobb SF intake and a GFB bpv.

datalog6.csv

datalog4.csv

datalog5.csv

No, you would need to go on our full etune, can't edit eric's maps.

-Brian

looks like i fixed my after reset/reflash low idle before warmed up problem. after resetting I fired up the car and then logged accelerator position, idle airflow and throttle position. I slowly started pressing the throttle pedal, rpm would dip to around 550 and shake, then start to smooth out as I continued applying more throttle. in the logs I saw that as soon as I started to touch the pedal, idle airflow would suddenly drop from ~ 4.9-5.1 to a flat 3.33 and the low rpm and shaking would start. logged throttle position would dip to 2-3%. figuring that the minimum throttle position my car needs to idle smoothly after warmed up and all learning has happened is around 4%, I edited my Idle Airflow Targets table to specify throttle position of 3.60 at all idle airflow below ~5 g/sec. I flashed that revision, started it up cold, started to slowly press on the throttle pedal and rpm dropped only very very slightly before increasing in relation to continued pressing on the throttle pedal. before it warmed up I then went out for a low speed low throttle local drive. gone is the rpm dropping and bad shaking right after ECU reset/reflash. Wish I'd bothered w/ this 3.5 yrs ago. I've flashed hundreds of revisions over the years and have put up w/ this nuisance the whole time.

YMMV w/ changes like what I made but it appears to have worked well for my situation.