RB25DET idles weirdly after warming up

[GabRB26DETT]

Hey all, yesterday, I came back home and when I turned on my street, my engine started stalling and dying out. It was in 1st and I had to keep revving it gently to avoid stalling. It lost all power and wouldn't go above 5km/h.

I wanted to go park it, but 500 meters before my house, everything went back to normal.

First thought, was to check the MAF sensor. I noticed that my HKS filter was disintegrating and had let some particles past the MAF sensor and most likely into the intake, very few though, since most of it was caught in the mesh.

I disassembled it and cleaned it using MAF sensor cleaner and as advised in another post, reset my ECU but unplugging the battery, pressing the brake 3 times and giving it 15 minutes.

Obviously, upon restart the engine was cold, so it idles at about 800-1,000 RPM. I went ahead and warmed it up driving and did a few pulls. No stuttering or any power issue, sounds and feels healthy.

After parking, it started idling strangely like this :

Engine from Cabin - Streamable

Here's what it sounds like from the outside, hear that strange "high pitched" sound ?

Engine from bay - Streamable

I'm no mechanic, but could it be a faulty MAF sensor or idle air control valve ? I'm curious as to why it only happens after the engine warms up though.

I got the car over a week ago, it's 100% stock besides a boost controller set on low boost and this just started.

Thoughts ?

[KiwiRS4T]

CAS looks pretty weather beaten...maybe check the bearings? And of course clean the IACV.

[GTSBoy]

Let's start with the obvious. You, that is you, will have to work out where that noise is coming from. It is probably unrelated to your idle problem. It sounds like it might be the power steering pump, or something else rotating down there, simply because of how it appeared to get louder when you pointed the camera there. But the CAS is in the same general area, and it could be noisy/dying bearings or some other rubbing problem in there. But we can't find the source of the noise across the internet. Put some time and effort into working out where the noise is coming from. Do you know how to use a length of hose to find noises?

Then the idle. I haven't seen such sudden, short, small changes in idle speed before. When my IACV is dirty/sticky and not responding to the ECU's drive signal properly, it will jump up to really high revs and behave much worse than that. Nonetheless, I would suggest that what you are seeing is the ECU responding to something changing (engine load caused by PS pump, possibly the rpm signal derived from the CAS) and simply driving the IACV more open/closed in response.

[trel]

The revs if warm seem high. Did you make sure when you reconnected everything that it's all tight? Sounds like a hiss. That engine bay looks pretty weathered and I would hazard a guess and say some rubber hoses have split from being brittle after you moved the maf around.

[GabRB26DETT]

5 hours ago, KiwiRS4T said:

CAS looks pretty weather beaten...maybe check the bearings? And of course clean the IACV.

Yeah, the idle air control valve was my first thought, but I wasn't entirely sure, considering the fact that when cold, it seems perfectly fine. I'll look into it tomorrow !

[GabRB26DETT]

3 hours ago, GTSBoy said:

Let's start with the obvious. You, that is you, will have to work out where that noise is coming from. It is probably unrelated to your idle problem. It sounds like it might be the power steering pump, or something else rotating down there, simply because of how it appeared to get louder when you pointed the camera there. But the CAS is in the same general area, and it could be noisy/dying bearings or some other rubbing problem in there. But we can't find the source of the noise across the internet. Put some time and effort into working out where the noise is coming from. Do you know how to use a length of hose to find noises?

Then the idle. I haven't seen such sudden, short, small changes in idle speed before. When my IACV is dirty/sticky and not responding to the ECU's drive signal properly, it will jump up to really high revs and behave much worse than that. Nonetheless, I would suggest that what you are seeing is the ECU responding to something changing (engine load caused by PS pump, possibly the rpm signal derived from the CAS) and simply driving the IACV more open/closed in response.

I'll start with trying to give the idle air control valve a clean up.

Also, I just noticed something strange. I was watching a video on cleaning up the IACV, and it mentioned unplugging the TPS connector and adjusting the IACV screw to set the idle. I checked on mine, and for some reason, the cable seems deleted, but the connector is still in. It was always like this, so I doubt it's THE issue, but still doesn't seem normal nonetheless !

Any thoughts about that ?

 

[GTSBoy]

2 hours ago, trel said:

The revs if warm seem high

It's idling at 600rpm. If anything, this is slightly low, not high.

6 minutes ago, GabRB26DETT said:

Also, I just noticed something strange. I was watching a video on cleaning up the IACV, and it mentioned unplugging the TPS connector and adjusting the IACV screw to set the idle. I checked on mine, and for some reason, the cable seems deleted, but the connector is still in. It was always like this, so I doubt it's THE issue, but still doesn't seem normal nonetheless !

Any thoughts about that ?

This is a major WTF!!!???!!??. The standard ECU needs the TPS. It cannot know you are at idle if it can't see ~0.45v coming back from the TPS. It also uses it elsewhere in the operational range to know about "accel pump" functionality, and so on.

 

7 minutes ago, GabRB26DETT said:

I'll start with trying to give the idle air control valve a clean up.

It won't be the IACV. As far as I can tell, it appears to be working. The way your tacho moves by small defined amounts looks like the idle speed is responding to the ECU changing the opening of teh IACV.

[GabRB26DETT]

3 minutes ago, GTSBoy said:

This is a major WTF!!!???!!??. The standard ECU needs the TPS. It cannot know you are at idle if it can't see ~0.45v coming back from the TPS. It also uses it elsewhere in the operational range to know about "accel pump" functionality, and so on.

That is the part that I don't get. It was working flawlessly before yesterday. I even looked at pictures sent by the seller before I bought it, and it was indeed this way. 

I mean, don't get me wrong, the car performs really great and sounds absolutely healthy whenever it's not idling, which confuses me.

 

[tridentt150v]

Others have covered the idle issue..and they are right its bloody hard to diagnose on the internet.  Its a challenge for you and your mechanic.

Looking at all the white 'powder' in the engine bay plus the noise...I'd say you have [or have had in the past] a water pump issue.  Does it leak at all?

 

[GTSBoy]

I just had another look. There are 2 loom plugs on these TPSs, and the lower one appears to be connected.

I have little direct experience with playing with these on vanilla RB25s. RB20s had a similar TPS, but the ECU used it differently. And the TPS on my 25Neo is essentially the same as vanilla 25, but I haven't had to mess with it. So I've forgotten which plug is which. You may have no real problem here, depending on what is disconnected.