Ultra_Dog

I can't seem to figure out why my idle always holds at about 2K after hitting boost and bringing the car down in speed. The only workable solution has been to turn the engine off and restart it (while at a full stop) and then the idle will return to normal.

I have a BBK 52MM TB.

onlyone07

I don't think it has much to do with getting into boost, because my BBK 58mm does this on my n/a car. It drives me crazy, but I think if the TB is kind of old it starts to stick open slightly. It might need a good cleaning or maybe a rebuild if you know of anyone local who can do it.

Kevin Blown 95 TA

I had to put a second return spring on my throttle body cause it always stuck open a little since I put it on causing the annoying high idle problem. If you can get it to stick in that high idle mode, quick open the hood and see if you can close the throttle body blades and if it helps. It'll show you which dirction to go.

Lonnie Pavtis

The BBK throttle bodies have the throttle lever crimped onto the shaft. After hitting full throttle it moves. The throttle stop is on the lever so it changes the idle speed.

When you return to idle, the TPS sees a small % of throttle opening & does not think you intend to idle, so the IAC does not correct. By restarting, it rezeroes itself & works fine.

Get someone to tack weld the lever to the shaft & it will be fine.

Kevin Blown 95 TA

Good point Lonnie - that was a known problem with those. I had tig welded mine before I ever installed it due to a tip in a magazine & still had the problem intermittantly. My rpm would go up to 1100 or so, nothing too drastic, just annoying. I tried resetting the blades in the bores & that didn't help. I tried opening the blades a little bit too. I also thought there was a little interference from the plastic cover, so I ran w/o that for a while and that seemed to get rid of most of it, but in the end, I added the second spring to completely fix it. With a ball bearing movement, you'd think it would never be sticky - I never figured out exactly what was hanging it up.

canbaufo

How involved is adding the second spring? I have the same problem with my 58 MM BBK. Especially when it's cold. Mine acts weird sometimes though, as in I can creep along at 1 MPH and it will idle at 1,200 rpm but if I come to a complete stop it goes to 900 almost immediately. Maybe the PCM says "ok, you're stopped for a second ...so the IAC should start working even if you do have the throttle tilted open a bit". I dunno. What I do know for sure is one night I ran it WOT a few times and the high idling was worse than ever ...hitting about 1,500 no matter how long I stayed stopped. That kind of answers my own question though ...obviously the PCM won't say "it's time to adjust IAC since you're stopped" or it would have in that case. I'm not sure what the other scenario really is ....weird, I'm not joking I can be going ~1/2 MPH and it stays at 1,200 or so, then I stop and it goes to 900. I don't remember seeing anything in the programming that says there are IAC steps at ~1 MPH ...maybe so though.

Anyway, sounds like the second spring being added is the best fix. I've also noticed this thing doesn't hold back much when going down a hill in a low gear ...this may have something to do with the throttle blade being partially stuck open. I feel like I'm really wasting brakes and gas having to brake so much when going down a hill in a low gear. So how involved is adding a second spring? ....too cold to go downstairs and look at it right now lol.

Something to take into consideration though .....this problem actually aids compressor surge and makes it easier on it on decel and shifts since the blades are tilted open allowing some air to get through. I think it's annoying though....besides, that's why I have a bypass valve on it.

Camaro_SS/R

For me what fixed it was
1. the blades were sticking or more accurately shifted (when aftermarket TB is old) so one side of the blades was sticking to the TB. If you pull the TB and have light shine from the back you can see where it may be sticking. I took some sand paper and sand down the blade to allow it to fully close without any sticking.

2. Step one solved most of the problem. Another thing I played with later on is in the PCM specifically the Close throttle spark advance and IAC Throttle follower vs MPH in LT1 Edit.

Kevin Blown 95 TA

Adding a second spring is as simple as going to the hardware store and buying a couple different ones from the selection in those drawers and finding a point to hook it up where it doesn't rub on anything. I might have had to drill a couple small holes to make mounting points, and I experimented a little bit with tensions, positioning, & cutting the springs, but I after I installed it, I forgot it was even on there and the problem was gone. You need only a little bit of extra tension, so don't go overboard.

A second spring is always a good idea anyway, cause what if the other one lets go?

I would post a pic, but it's all apart now to rebuild the engine.

canbaufo

Well, it's good to know there are some fixes ....sanding the blade down sounds pretty easy. I've never disconnected a throttle cable, is this easy to explain how to do?

What works best in the IAC vs throttle follower programming? I've tried playing around with it but it seems to have no effect. This thing always idles at like 1,500 when moving over say 20 mph even if it's not stuck open (I think anyway).

Sanding the blade down where it rubs seems to be the most practical way to fix it, but a second spring isn't a bad idea anyway.

The throttle lever moving after hitting WOT so that it rest on the stop differently is sh!tty too. Jeez, this thing needs a few fixes it seems ...freakin' junk. Thanks for the tips, should be fixable one way or the other.

Kevin Blown 95 TA

I couldn't disagree more. If you think disconnecting a throttle cable is a hard job, don't even mess with sanding your butterflies. Try the spring first, and if that doesn't work, then try something else, but don't sand the butterflies. If you think they are the cause of it, then loosen the screws that hold them to the shaft and snap it shut once or twice and then retighten them.

canbaufo

No, I'd say it's pretty easy ...I've just never done it but could figure it out I'm sure. I'd have to see for myself that the butterflies were the problem before I'd actually sand them. It almost seems like they'd have to be a cause of it regardless though, unless it's just a lever/stop problem. Thanks for the tip though, a second spring is really a given in light of potential failure of the main spring as you stated. I need to just go check it out and see what the issue really is, I just hate the cold so I've been trying to be a bench wrencher to figure it out before I start lol.

OBE1 95Z28

After I cleaned my TB I had a problem with the rpm hanging. I dabbed some oil on the butterfly rod where it means the body and the problem was cured.

Kevin Blown 95 TA

If you look closely at the butterflies, you will see that they are specially bevelled to seal up when they are closed in the bores. I can't imagine sanding them. If there is a nick causing a hangup, then dress it with a stone.

sprayedtransam

make sure you haven't blown the PCV valve off. My TA was idling horribly, turns out the boost had kicked the valve off the intake so I had a massive vacuum leak, it wouldn't idle at all below 1500...

Ultra_Dog

Update:
1) I called BBK (bbkperformance.com) and they asked that I check the throttle (at the TB) to see if the Hi-RPM is throttle related. So, I romped it and the idle was about 2K when I pulled over. Sure enough, I could close the throttle (a smidge) and the RPM dropped.

2) In the garage, I removed the elbow and throttle cable cover to inspect, found the throttle actuator assembly shaft is worn slightly. When I open the butterflies fully, then close them, they would remain open (thousandth of an inch or so..), but just enough to cause idle irregularies. I could manually close the butterflies by pushing the actuator closed. The TB spring was fully closing the actuator to the idle detent, but there is some shaft slop between the several parts, just enough to cause it not to close fully. Only happened if I went WOT, not partial. That explains the perceived relationship to boost, that really does not exist. I cleaned the ports (no sandpaper) and added a small 1 1/2" extension spring, but it is not very strong and is not fully returning the butterflies to 100% closed. I tried a stronger spring, but it was excessive.

Going to monitor it for a while. I am 4-years into the purchase, so warranty is not an option.

PS: Called BBK again and they were unaware of the problem, but this board surely sounded a common theme!! Seems that there is more to throttle-bodies than port diameter and price.