I just got a used ported TB, and I can see light around the edges of the blade when I hold it up to a light. I guess they got too eager porting where the blade and TB meet. What problems will I experience, and what can I do to fix it? Epoxy the TB? Epoxy the hole in the blade to compensate? Can it be fixed w/ tuning? Thanks in advance for the help.

 

You can swap blades from your old one to the ported one.

 

it might idle alittle high... compare it to a stock tb
also, you might want to try it to see if it does idle high

 

You might be able to compensate by closing the set screw too. It's not a lost cause yet. Find someone with a scanner who can watch your IAC steps once your engine is up to operating temps. Let the motor cool and install the new throttle body. If the IAC steps are lower with the new throttle body once the engine is back up to temp again, close the set screw until they come back up to where they were before the swap. If you close it all the way and they aren't as high, then the throttle body may be more trouble than it's worth...

 

Thanks for the info, guys. So my understanding is that the problems I might run into are:

- higher idle
- lower IACs

I'm hoping I can just swap my blade out, but just a quick look suggests they cut more material from the TB than the blade. I'll check it out anyways, becuause that's gonna be a pretty easy fix if it works.

As for IACs, what will lower IACs do to the way the car runs? Will the car run leaner, or does it simply affect idle/surging issues (seems like idle/surging only, from what I've read)? Also, can the PCM learn to compensate? I've heard that you should let the car idle for 15 minutes after changing TBs to let the computer get used to the new TB. Would that solve anything, or is it more of a band-aid to the real problem?

One last thing: If I put the TB on, and have no idle issues, does that mean it's all good? Or do I have other parameters I should be worrying about as well? Thanks.

 

The IAC is a valve. It's range of operation is identified by "steps". The higher the number of steps, the more the IAC valve is open. Because it behind the MAF, it's measured airflow. So, it shouldn't affect fueling. If the steps are too low, the side effect is unwanted higher idle speeds. It may contribute to surging - but not likely. In terms of airflow, the PCM learns where it needs to be rather quickly. 5 minutes after the car is up to temp, it should be good. If you have an auto, it's 10 minutes (5 minutes in gear and 5 in park/neutral). Either way, you should find someone with a scanner like I mentioned above. Note your IAC steps with the car up to temp. Make the swap and note the steps once it's up to temp again. If it's close enough, you can tweak it with the set screw.

 

When I got my ported TB I too noticed light around the edges but I put it on to see anyway. It did idle about 500-700 rpm higher than stock at first startup...drove it around a while and idled only 200-300 rpm over stock, and gradually went back down over the next day or so. It is now back at stock idle and all is good, so I think the computer just had to re-learn the air-flow.
I say put it on and see what happens over the next day or so.

 

Pretty much if comes to a normal idle on a cold morning, you're fine. Fine tuning like SSpd suggested would be nice, but may not be needed if the light is small. On a stock TB, the blade is not perfectly sealed, so a little light may not be the end of the world.

BTW, if the gap is big enough to create idle issues (i.e. IAC counts drop to zero), don't panic. Close the hole in the blade with expoxy and see if that cures it.

 

Im sure it wont cause problems unless its a big gap, buts its probley real small.

 

Thanks for the great info, guys. I was planning to get HPTuners soon anyways, but I'm hoping I can run the TB before then.

Thanks for the clarification on IAC steps, SSpdDmon. I'm going to try reading up more on IAC counts and what's good, bad, etc. Are there any other documents I should look at besides the stickies in the PCM Tuning forum?

BTW, is camming the car a good way to fix a low IAC count?

 

There's a ton of info in the PCM section. That's where I'd send you to search for more info. As for a cam...that's not really what affects the IAC. Basically, there's a table in the tune that tells the PCM how much airflow the engine needs at idle for a given coolant temp. The PCM uses this as a base airflow number, makes minor adjustments in the short term (short term idle trims), and learns the trends of those short term adjustments over the long term (long term idle trims). Ideally, you want your IAC at a warm idle around 60~70 steps and the average of your STIT's + LTIT's close to zero. IAC steps are fixed manually by opening/closing the set screw or drilling the throttle body blade. The idle trims are changed by altering the table in the PCM. So, camming the car isn't the fix for that....but it's definitely a fun mod.

 

I bought a ported TB off of here that was ported around the blade .. around .010 clearance around the blade (Wow!). I countersunk both sides of the hole to keep the filler from falling out) then JB welded it ... sanded flush.

Runs perfect!

 

You should see a "crack" of light all the way around the blade on a ported TB. What you are seeing is the clearance that is machined in from GM unless it has really been overported. If you dont see any light at all then its gonna stick. The reason you cannot see any light on the stock TB is because the ridge is there blocking the view of it.

 

I'm agree with Bo. I have ported and sold about 40 tbs, and everyone of them you can see a little light. It will not affect any thing. If it does idle a little high, then the pcm will correct it

 

What ive done if its ported right, is take and filled in the hole in the blade itself...

 

I am on about my 6th port and polish job and once you even just clean them out you can see light all the way around. I have had one person say it surged 50 rpms when he first got it but it quickly learned the new idle. I think it had more to do with the car being used to the gunk around the throttle blade than anything else. I wouldn't worry about it unless it really causes a problem on the car.

 

First, thanks for all the info, guys. All of it helped out.

Now, for an update.

Ported TB, throttle blade knife edged, half shaft, holes epoxied.

I put the ported TB on just for the heck of it, to see what would happen. I drive it around, and the idle's all over the place, usually 400-500 rpm high for a few seconds when clutching in and coasting, and holding at 1100-1200 rpm for at least 5 seconds. It then slowly crept back down to 1000 rpm or so. I threw an SES light after ~30 minutes of driving, and the idle refused to calm down.

Here were the steps I took to try and fix the problem:

I first adjusted the idle set screw to pretty much nothing and reset the PCM. This took care of the SES light, and when I fired it up, the idle stabilized nice and low. I drove it around for ~5 minutes, and it seemed fine. The car was learning to put more air in to keep the idle going, and it seemed okay.

The next morning, I take it for a spin, and I'm meeting a little resistance on the pedal when going from zero throttle to partial throttle, as if the throttle cable or the throttle blade was sticking. I figure that it may be the blade, since it seemed to stick for some reason when I turned the throttle cam by hand with the idle set screw all the way out.

I screw in the idle set screw a little bit, reset the PCM, and try again. Idle's still fine, but I still get sticking. And I can't even duplicate the sticking by turning the throttle cam by hand anymore. I keep trying this a few more times, to no avail. I even try to loosen the throttle blade screws a little bit, thinking that maybe by keeping them a little loose, it won't get stuck. Didn't help. Strange thing too, since I didn't feel this sticking with the engine off and just pressing on the gas pedal. It only stuck when actually driving. And sometimes, it would feel fine for the first few minutes, only to start sticking again the next morning.

I thought about changing the whole shaft over from my old TB, but figured I'd try switching throttle blades first, just for ***** and giggles. Put my old throttle blade on, and most of the light around the edge of the blade is gone. A sliver compared to what I had with the knife-edged blade. I turn the cam by hand, and the blade doesn't stick, even though it seems to have more material.

So I throw it on the car, reset the PCM again for the eighth time or so, and fire it up. The engine's struggling to get enough air, but it manages to stay alive. I take it around the block, and there's no sticking. Next morning, I try it out again, and there's absolutely no sticking at all. Seems fixed.

Just in case, I readjust the idle set screw to let in more air and reset the PCM one last time. I fire it up, and the engine no longer struggled for those first few seconds after a PCM reset.

I end up with a ported TB, better throttle response, no sticky throttle, but no knife-edged blade. Beats me why a stock blade with more material doesn't stick while a knife-edged blade with less material doesn't, but I won't argue with the results. I tried that knife-edged blade both ultra-tight and slightly loose, and neither made a difference.

I didn't use a scan tool to check IAC counts, and I don't know if resetting the PCM and observing how the car compensated for the idle was the proper way to do this. Let me know if that's not a logical approach.

Thanks for all the help, guys. Just glad such a simple fix did it, even if I can't explain why.

 

The throttle blade can stick after you half shaft it. The last one I did was like that because when you tightened the blade down there wasn't that other half of the shaft to make it line up perfectly. Check to see if this is what is happening. If it is take teh TB off and hold it up to the light as you cycle it through. You should be able to see where it is sticking. After that just take a piece of sandpaper or a sanding drum on a dremel and sand a very small amount of the blade to make it fit. Just do a little bit at a time until it fits.

 

mine idled 200rpm higher than normal for about a week, then i guess it finally adjusted because it idles like stock now, and i wasnt careful at all around the bore where the blade seats...