Correct me if I'm wrong, but the electric throttle body uses the throttle plate for idle air control, right?

When I blip the throttle, the engine will lose revs and nearly die before returning to idle. Scanner shows absolute throttle position bouncing around between 0% to 3% while the engine is trying to return to idle. No codes, no lights.

Additionally, I found that when I press the pedal just a little bit, I can can cause the revs to drop.
At idle, the absolute throttle position is around 1.6-2%. When I just barely press on the pedal and hold, the throttle position will change to 0.4% and rpms will drop to around 400. As I press the pedal more, the absolute throttle position will steadily increase.
My understanding that this should not happen, right? Shouldn't the electronic idle control maintain at least that 1.6-2% absolute throttle position in order to maintain proper idle, regardless of my pedal position? Maybe someone else can test this in their car and provide results.
If this is abnormal as I suspect, does anyone have any idea why such a thing would occur?

 

Not to take this away from the TB but, it sounds like you have an unmetered air leak between the MAF and the TB to me. Clean the MAF and check for any air leaks especially on the underside of the corrugated air pipe where the plastic gets cooked.

 

With electronic throttlebody plate opening amount in relationship to the pedal position is not at all 1:1. It is everything in between and fully live adjustable via ecu. Look what does egr do the same time when you press the pedal. As egr is dirty air and therefore air is passing through it, plate is not needed to turn that much. And of course there is a possibility of unmetered air. In other makes of cars rpm's that dippes clearly under the target idle speed when coming from the higher rpms issue is pretty much always dirty tb. This is because tb idle opening area is pretty small in degrees and air gap between body and plate is narrow. When ecm always ofcourse turns the plate to idle area carbon from the egr gas starts to bild up to the idle area of the body thus reducing airflow what normally would be enough to achieve target engine idle speed.

 

Update:
Cleaned the Throttle Body
Cleaned the MAF
Looked extensively for air leaks in the intake elbow and full load breather - couldn't find anything
Looked for vacuum leaks with ether - couldn't find anything

The rpm drops after bliping are not as bad now, it only drop to around 500-450 instead of 400-350. That being said, it still does have some sort of issue.
Fuel trims are also immaculate.
Not sure where to go from here.

 

I would carefully adjust your TPS while the engine is up to full operating temperature. You don’t really need a data list readout of it. Just adjust and lock it in place and see how the engine reacts to it. I’ve done it that way before.

 

Aye sounds like a TPS issue to me, I'd had similar on bikes.

 

How would one go about adjusting the TPS?

 

Does it drop under target rpm when you let off the gas from steady rpm ? Lets say 2000rpm ? Very quick blip may too be too fast to ecm catch the rpm drop. I would not touch the tps if not neccessary. When you do this steady rpm test. Will the ecu catch rpm top of the target and slowly lower it to the target? Or does it fell straight under?

 

Unmetered air leak - can of brake cleaner, puff it around and see if revs rise...leave the TPS for now...cracks or leaking gaskets you won't eyeball.

 

Yep...sounds like it's drawing more air than fuel, causing the rpm to drop.

 

Check for air leaks; but also take the slack out of accelerator cable.

I guess I can search for it, but how do you adjust the throttle valve?

 

"Does it drop under target rpm when you let off the gas from steady rpm ? Lets say 2000rpm ? Very quick blip may too be too fast to ecm catch the rpm drop. I would not touch the tps if not neccessary. When you do this steady rpm test. Will the ecu catch rpm top of the target and slowly lower it to the target? Or does it fell straight under?"
When I let off gas from a steady rpm, the ecm does catch the drop properly. It's only on short blips that it falls under, and when I decelerate to a stop.

As for air leaks, I have checked around with a can of ether and have gone through the engine 3 times. I've done everything short of a smoke test. Speaking of which, any of y'all know a cheap way to do a smoke test?

Accelerator Cable is properly adjusted as per the manual, I checked that a couple of weeks ago.

I agree that it's likely a vacuum leak, but I just can't find where it is.

 

I'd say tha your're car is a ok. When there is no trimms that are off limits and engine runs fine that is then a feature, not fault.

 

I'd agree with you except that the rpms sometimes dips low enough that the engine almost stalls when I decelerate to a stop. It did actually stall once. The car also hot starts with a very lumpy idle (jumping between 400-600) sometimes.

 

In ocassional problems it is better to have livedata from the engine in hand when problem is on hand. Only then you may be able to see what is goin on. Otherwise it can easily be just guessing.

 

I might have missed it in the thread, but have you cleaned the throttle butterfly & venturi? I've seen idle issues on other cars due to a ring of oily carbon where the butterfly sits at idle. I think if the gunge builds up too much it blocks the air within the ECU's expected idle speed opening & then it has to react by opening further.

 

I have cleaned the throttle body.
I will try to get data during the occasional problems.
In the past, when the engine was having trouble, the STFTs would be around 5% positive at idle (normally it's around 0). Lamba ratios were good. I do not recall what the absolute throttle position was doing, which may be important, so I will try to get that information.

 

Everything under + - 5% of stft and ltft is completely ok and normal wear and tear.

 

I noticed the car was running exceptionally well today so I tested blipping the throttle and it was able to return to idle normally.
Out of curiosity, I shut the car off and turned it back on. This time it was back to its old ways of rpm dropping after blipping.

To summarize: Car normally runs bad. Car ran fine. Car ran bad again after cycling the ignition.

This sounds like an electrical issue, no?
Or is an intermittent vacuum leak a thing?