throttle body shaft seals/idle surge

[turbowop]

So ever since I got home from a DSM/Evo meet I went to in June with 1051, the car has had an idle surge issue. I'm just now getting to diagnose it. I tested the ISC and it tested out fine, but swapped it with the one in 503 anyway and that's not the problem. Car has a blocked off FIAV and EGR. BISS is set correctly as well.

So I boost leak tested it. At about 10psi, the throttle body shaft seal on the TPS side starts leaking a steady stream of air. I could feel it coming out from under the TPS, so I removed it and the shaft seal is definitely the problem. Would this leak/suck enough air at idle to cause a surge issue? Since the shaft seal is technically between sides of the throttle plate, I wasn't sure if enough air could get sucked through it during vacuum to cause surge. I have a couple of seals here I purchased years ago that I could install, but figured I'd ask anyway. Pulling the TB apart to replace these looks like a pain in the ass. /ubbthreads/images/graemlins/crazy.gif

 

[Terry Posten]

Yes it can. It takes very little to make that happen.

Meter the TPS. while metering it, make sure that the ohms are not jumping around and it has a smooth "scale".

Also, what is the condition of the ECU? Take a quick ,look to make sure there is no acid damage.

Also, do you have the TB grounded?

 

[turbowop]

Earlier tonight before I realized where the leak was actually coming from, I thought it was coming from the bottom of the gasket between the intake manifold and the throttle body, so I replaced that gasket with a new one. Now that you mentioned the TB being grounded I went out and checked a couple of things. First thing I checked with the logger when the surge started, was the idle switch, which was working. Since I've replaced the gasket, it's not, so I checked TB continuity to ground and there isn't anything. I jumper'd the TB to ground and now the idle switch is working. I'll have to see if this is the issue before I tear into the throttle body to replace the seals. If this fixes it, I'll leave the TB alone, since the boost leak at 13psi was pretty damn minimal, IMO. I've always been able to hear a little bit of air at the shaft seals over the years and it's never caused any idle issues. The car has no other boost leaks at all.

ECU was socketed and caps replaced by Jeff forever ago. If I recall, there was no leakage at the time, but he replaced the caps regardless. I'm pretty sure the ECU is fine. TPS is nice and smooth as well.

I'll keep this updated as I sort through the issue.

 

[turbowop]

Got the TB grounded. I'll fire up the car and test this out tomorrow. If I start the car up at midnight right now, my neighbors might get a tad angry. /ubbthreads/images/graemlins/hsugh.gif

Hopefully this fixes it. It sure was acting like a bad idle switch. It would surge up and down when coasting to a stop, then when finally stopped it would just idle at around 1300 rpm. It wouldn't bother me so much but surging with a twin-disk sucks. Whenever it hits the low spot on the surge, it dies. It's bad enough being at a stop light with the twin-disk rattling around, let along the car dieing and having to restart it. /ubbthreads/images/graemlins/rofl.gif

 

[Polish]

Quoting turbowop:
Pulling the TB apart to replace these looks like a pain in the ass. /ubbthreads/images/graemlins/crazy.gif



It's not really, actually pretty easy. The spring may go flying but if you're careful it won't, either way there isn't really much to the TB at all once you get it apart.

- Edit - Oh and if the TB was not grounded and is now it should help out. I forgot my ground once and it did pretty much what you re describing. Once I reattached it it was back to normal.

 

[turbowop]

I'll find out after work today. I just don't understand why it started doing this out of nowhere. I haven't had an actual ground wire on there for years. /ubbthreads/images/graemlins/dunno.gif

 

[Hertz]

Just replace the seals already. /ubbthreads/images/graemlins/hsughup.gif

 

here's what you need.

click

 

[boostedinaz]

Rebuilding the TB is super easy. The biggest thing to remember is before you take it apart get a Sharpie and draw a line on the TB return spring. This will make it super easy to set the proper tension when you put it back together.

Oh and search you freakin' noob. /ubbthreads/images/graemlins/rofl.gif

 

[turbowop]

I already haz teh seals, but I'm lazy. /ubbthreads/images/graemlins/grin.gif If the ground fixes the issue, I'm holding off on a TB rebuild until the leak is worse. It really is pretty minor, IMO.

My question was really whether or not such a minor leak could cause the surge. I would expect it to require something more like a disconnected vacuum hose. Guess I'll find out later.

 

[jepherz]

I often wonder if other cars (newer cars) even have seals on the throttle body shaft. Anybody know? Leaks like this don't seem like they'd matter on a lot of newer cars since they are map based, and I never hear of any other make rebuilding their TBs.

 

[turbowop]

So I zeroed out the ISC/set the BISS and took it out for a drive. Problem solved. Thanks for the idea, Terry.

Still pulls hard, so I'll save the TB rebuild for another day. /ubbthreads/images/graemlins/grin.gif

 

[NateCrisman]

Oh man, just change those TB seals. That little tiny boost leak could be like turning the "pulls hard" amp up to 11 /ubbthreads/images/graemlins/grin.gif

 

[turbowop]

I honestly don't think it's robbing any power. It's very minor. /ubbthreads/images/graemlins/dunno.gif