What is this part?

liquidefex

liquidefex

Greenie N00B Member
Greenie Member
I've been struggling after a full engine rebuild lately, so anyone's input would be appreciated!

Got everything back together, started the car up and it is running kind of weird. No real mods besides a few bolt ons. New turbo inlet pipe, cobb intake, rebuilt stock K04 turbo, balance shaft delete, and that is about it.

When I first fired up the car, it runs at a really high idle, like 2k, then after five or so minutes it drops down to 1200, then starts surging between 1200 and 1800 on repeat.

I pulled the codes initially and got
P2122 Throttle/Pedal Position Sensor/Switch D Circuit Low
P0089 Fuel Pressure Regulator 1 Performance

I did a little digging and people suggested replacing the accelerator pedal, so I did that...and now I have three codes and the engine runs significantly worse. Struggles to maintain an idle around 1k and sounds really rough. The new code is:

P2128 Throttle/Pedal Position Sensor/Switch E Circuit Low

After which I got curious about the actual throttle position sensor under the hood, which looks like the attached photo because I thought something might be wrong with it...but in the process I broke a small white plastic piece which that throttle position sensor actuates on a different component under the hood.

After I broke that piece off, now the car won't start at all. Still cranks fine and sounds like it is very eager to run, but I have to replace the piece I need help identifying so I can get back on the problem solving track.

So I have two questions, first of all, what is the name of the part with the greenish/greyish dome shape in the other attached photos.

And two, any ideas on a possible solution for the surging idle?

Thanks so much for your time!
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Are you sure all the vacuum lines and clamps and all that are plugged in properly? Do you have a way to monitor or log? Also if you're really in Tucson I might be able to come down and take a look.
 
Yeah I am in Tucson, west side near Star Pass! If you ever wanna come down, I got lunch and a few beers for ya. I am...probably 98% sure I have all the vacuum lines and electrical connections plugged in properly. I have bluedriver for my phone, so if there is some way to monitor/log via that app then yes I do.
 
Torque App. Things to look for are Manifold pressure, AFR, Throttle position, MAFv, Fuel Rail Pressure.
 
Sounds good. You wouldn't happen to know what part I'm referring to, would you? I think I have to get that replaced before I can get the car running again.
 
It looks like it's for the VCTS system; the flappers on the intake mani.
 
Yeah that's the VCTS control flappy deal (technical term)
 
@Enki did that VCTS fix and replaced the purge valve and the car is running amazing right now. Really happy with it, now I am just curious about the sound/volume of air being sucked through the intercooler by the turbo. I did a pretty good vacuum leak check this morning, sprayed brake cleaner lots of places to see if I could hear any changes and I got nothing.

This is a link to a video of the sound I'm talking about if you want to check it out:

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Tomorrow morning is new outer tie rods, ball joints, CV axles and rear stabilizer links, then it should be ready to drive.

Excited to get it back on the road after this full rebuild!
 
That sounds like a vacuum leak. Get the information from ODB2 that I referenced previously to confirm.
 
Dude I couldn't find ANYTHING spraying brake cleaner all over the engine bay. I'll get some more data in a little bit and post some stuff here.
 
Let's step through the columns in the order I checked them:
1. Throttle position: Steady state, a little bit of variance. Looks like you're sitting at idle; no issues here.
2. LTFT (long term fuel trim) Steady state 0; either trims are good or not adapted yet; acceptable.
3. IAT (intake air temps): Nothing out of the ordinary here, some fluctuation is expected, especially if the fan kicks on.
4. Throttle: Looks pretty steady state, with some variance. As expected, nothing jumps out here.
5. Short term fuel trim: Issue spotted, went from adding 25% fuel to adding none...Why?
6. Intake mani pressure: Big drop in pressure suggests a sudden influx of flow or a leak allowing a large amount of air past the throttle (blipping it, but we know this isn't the case)
7. Massflow (mass air flow rate): I don't know if you know how much air actually weighs but in one cell you went from 6 grams per second airflow to 20, all through the mass airflow sensor, and with no throttle movement.

There are a few possible causes for this:
1. Some kind of weird leak (which seems to be audible in your case)
2. The TPS (throttle position sensor) is not working right
3. There is a problem with the airflow over the MAF (doesn't seem to be the case, as flow is relatively steady until it rockets up briefly)

Further Testing:
1. Try to isolate the source of the sound, using a hose near your ear (don't put it IN your ear, just use it like a directional funnel for the sound)
2. Log again, but with RPM and accelerator pedal in the list, and blip the throttle. If the pedal matches TPS and RPM, TPS is registering fine. Keep in mind these cars are drive by wire so some variation in TPS is expected as the ecu will adjust that to hold idle, etc.
3. Pull the filter and look down the intake. Is the MAF dirty? Anything obstructing airflow? Does it run better without the filter? (Don't run without a filter for a long time, just long enough to test/log and don't blip the throttle if you're not 100% certain that there's nothing that will get sucked into the turbo)
4. If you are using a thick thermal gasket on the intake manifold, make sure that there's some kind of spacer between the bottom mani bolt (the one closer to the starter than the TMIC) as if this is not present it won't let your intake mani sit flush. As a quick test, you can loosen this bottom bolt and see if that noise goes away.
 
Okay as far as stepping through them, I am pretty sure I may have blipped the throttle once or twice, so a few of those readings being slightly wonky could've been because of that.

Now jumping down to your possible causes for this:

1 - probably yeah, I will grab a hose, shove it into my brain via the ear canal, and see what happens
2 - this has been in the back of my mind for a little bit, but I not getting any codes at the moment and the throttle is responsive. One other symptom however is that sometimes when I blip the throttle, or when I hold it around 2-3k and then let go, the idle gets too low and the car dies.
3 - Again with the MAF rocketing up briefly, I think I blipped the throttle, I also took the MAF out yesterday and cleaned it so it should be good to go.

I'm curious about #4 in your further testing...when I put the intake manifold back on, I had five of the same bolts, and I torqued them all down to spec. Was there a washer or something I forgot I took off of that bolt you're referencing when I disassembled?

For what it's worth, when I sprayed brake cleaner throughout the engine bay listening for changes, I hit the intake/pcv area as well as I could and never heard any changes, but when I sprayed it on top of/into the TMIC I heard a noticeable change in RPM, it was slight, but it was there.

I'm gonna go fire it up again right now, add RPM and pedal like you suggested, log, blip the throttle, and see what we get back.

I owe you bigtime boss!!
 
Don't shove the hose in your ear unless you want to risk a ruptured ear drum. I know it's very, very, very unlikely but seriously.

As for the lower intake mani bolt: start the car, loosen that lower bolt. If that sound goes away, you know where the issue is. Next step will be to pull the TMIC, retighten all but the bottom bolt (which you should take out) and see if you can stuff a nylon washer of the gap thickness in there to stiffen that up when you rebolt that hole (or just leave it unbolted, that's fine too for the most part).

If your TIG is thicker than stock, you'll wind up opening up a gap between the top of the intake mani and the head, which would explain the rev up you experienced spraying the TMIC (you'd be spraying through that onto the area where that gap would pull air in from).

Test and report back findings.
 
- Fired it up first time and it died.
- Fired it up second time, idle got VERY low, but it recovered and stabilized at idle. Let it run for 30 or so seconds and blipped the throttle, then it went VERY low idle and died.
- Fired it up third time, struggled to maintain idle, and it died.
- Fired it up fourth time, stabilized rather quickly. Blipped throttle multiple times (As you can see in data, at 18s, 50s, 68s), car didn't die until I had it key off.

This first excel file is from when I did the first blip and it died

This second excel file is from the fourth start, with multiple blips over the course of 90 seconds or so.

Interesting about the intake gasket, I will investigate that problem tomorrow. It's dark out now and I live in an apartment complex so working on my car is all but impossible at night.
 

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Loosened up that bolt on the intake manifold so it was backed out most of the way and made no difference on the sound. Now I'm researching how to build a homemade DIY smoke tester. Also popped the P2187 System Too Lean at Idle Bank 1, it's been stuck on for a while now.

Took it for a 20ish mile test drive while I returned a ball joint press, got some gas and stopped at a Big O for some air in the tires. I logged a bunch of data from the drive, figured I would post it to see if anything stuck out to you!
 

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Too lean means either your mafcal is off or you have a vac leak.
 
Welp, used your hose technique and I think I found the issue. This open hole on the bottom side of this...part...whatever it is...that bolts onto the top of the intake. It has other vacuum lines coming out of it but I have no clue where the missing hose is supposed to go!
 

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liquidefex said:
Welp, used your hose technique and I think I found the issue. This open hole on the bottom side of this...part...whatever it is...that bolts onto the top of the intake. It has other vacuum lines coming out of it but I have no clue where the missing hose is supposed to go!
Click to expand...
liquidefex said:
Welp, used your hose technique and I think I found the issue. This open hole on the bottom side of this...part...whatever it is...that bolts onto the top of the intake. It has other vacuum lines coming out of it but I have no clue where the missing hose is supposed to go!
Click to expand...


Wait never mind, it goes directly into the top of the intake. Fahk.
 
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