Idle problem after porting TB
02-25-2004, 09:06 AM
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Idle problem after porting TB I ported the ridge out of my throttle body the other day, filled the IAC cavity with epoxy and drilled the two holes for air to pass through (11/64" and 15/64"). I did not remove any material from the blade itself or the area surrounding it, and I did not remove any material from the intake side of the blade either.
After re-assembling everything, my car will not maintain an idle when I first start it up cold. If I don't give it any gas it will die immediately, if I give it a little gas after firing up then let off the pedal it will hunt for an idle VERY badly. If I keep giving it gas for around 30 seconds after firing up, I can let off the gas completely and it will idle smoothly for the rest of the drive. Drivability is great other than a slight whistling sound at part throttle around 2,800 RPM which I attribute to air rushing past the two small holes that I drilled. If I shut the car off after it's warmed up, then start it back up again it starts and idles fine.
I've only started and driven the car 3 times since porting the TB, but each drive was for approximately 30 miles. One last symptom: the first time I drove it, it seemed to idle about 100-200 RPMs higher than normal according to the tach., but since that first drive the idle speed has returned to normal which is ~850.
What could be causing the problem? Did I get the epoxy too close to the IAC valve chamber? Does it need some room to work? If that's the case, what are your suggestions for removing epoxy from that tiny area, the only way to access it is through the IAC bore which is pretty small. I was thinking about getting a small hobby file and trying to remove some of the epoxy that way.
Any other suggestions? Thanks!
After re-assembling everything, my car will not maintain an idle when I first start it up cold. If I don't give it any gas it will die immediately, if I give it a little gas after firing up then let off the pedal it will hunt for an idle VERY badly. If I keep giving it gas for around 30 seconds after firing up, I can let off the gas completely and it will idle smoothly for the rest of the drive. Drivability is great other than a slight whistling sound at part throttle around 2,800 RPM which I attribute to air rushing past the two small holes that I drilled. If I shut the car off after it's warmed up, then start it back up again it starts and idles fine.
I've only started and driven the car 3 times since porting the TB, but each drive was for approximately 30 miles. One last symptom: the first time I drove it, it seemed to idle about 100-200 RPMs higher than normal according to the tach., but since that first drive the idle speed has returned to normal which is ~850.
What could be causing the problem? Did I get the epoxy too close to the IAC valve chamber? Does it need some room to work? If that's the case, what are your suggestions for removing epoxy from that tiny area, the only way to access it is through the IAC bore which is pretty small. I was thinking about getting a small hobby file and trying to remove some of the epoxy that way.
Any other suggestions? Thanks!
02-25-2004, 11:52 AM
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Try resetting your IAC sensor. Start the car and let it run for a minute. Then shut the car off and unplug the IAC sensor. Start the car up with the sensor unpluged and let if run for another minute. Then shut the car off, plug the sensor back in and start it up again. You may also have to adjust the idle screw while doing this.
02-25-2004, 12:12 PM
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Check that there is no epoxy in the IAC bore
(remove the servo and inspect). The sealing lip
needs to be pristine and the travel bore should
not have anything that might bind or block the
piston.
Then I would go and enlarge the IAC feed
hole incrementally; the size may be a bit
small for what's needed and make the IAC
have to swing a lot to make any idle air
difference. I think I drilled mine at 3/16"
and this was OK (12/64") but there's no
reason why 1/4" wouldn't be better.
(remove the servo and inspect). The sealing lip
needs to be pristine and the travel bore should
not have anything that might bind or block the
piston.
Then I would go and enlarge the IAC feed
hole incrementally; the size may be a bit
small for what's needed and make the IAC
have to swing a lot to make any idle air
difference. I think I drilled mine at 3/16"
and this was OK (12/64") but there's no
reason why 1/4" wouldn't be better.
02-25-2004, 02:46 PM
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I think I will pull the TB off again and make sure the IAC area is clean, I'm not confident that it is clean right now. Anybody have any suggestions for how to get the area clean since the cavity on the intake side of the TB is already epoxied closed? I'm thinking a precision file set, X-acto knife, maybe some dental hooks/picks to chip away at it. Any other recommendations?
If this doesn't help, I will try resetting the IAC valve.
I'm not adjusting the idle screw though since it idles perfect after it warms up...
If this doesn't help, I will try resetting the IAC valve.
I'm not adjusting the idle screw though since it idles perfect after it warms up...
02-25-2004, 04:21 PM
#6
Chili pepper, it is possible for there to be epoxy bulit up on the inside. If you do what was suggested before (take off the IAC motor) and look inside, make sure there is a lot of room to let air get by. I had the same problem as you. once i opened it up, everything was fine!
02-25-2004, 04:24 PM
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I'd bet money that's what the problem is... I didn't spend a lot of time cleaning the epoxy out of the IAC area. 
I am going to stop by a hobby store on the way home tonight and see if I can find some good tools for working in such a confined area.
Thanks for the help everyone! I'll post the results if this fixes it.
I am going to stop by a hobby store on the way home tonight and see if I can find some good tools for working in such a confined area.Thanks for the help everyone! I'll post the results if this fixes it.
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02-25-2004, 08:48 PM
#9
I had the exact same problem after my h/c install. After dealing with it for 8mo and having it tuned by 2 different tuners, my bro and I switched out the ported tb for a stock one. The first few times, the hard starts were still there, but after turning the tb screw until it read about .6volts, it fires up fine now. NO more surging either. Drivability has improved 10fold. I'm thinking it has to do with the IAC hole being too small on the ported unit.
02-26-2004, 11:34 AM
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i would take a drill a little smaller than the diam. of the iac bore, and drill out the epoxy. the drill tip should be close to the shape that you need.
adjust the idle to about 800 ( stock is about 750-800)with the idle stop screw.
my wifes z28 has traction control so i had to mod the stops on the traction control motor to adjust it right, that way i can get a 90* angle at WOT,
and perfect idle.
adjust the idle to about 800 ( stock is about 750-800)with the idle stop screw.
my wifes z28 has traction control so i had to mod the stops on the traction control motor to adjust it right, that way i can get a 90* angle at WOT,
and perfect idle.
02-28-2004, 10:23 PM
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Well, I'm not sure which of the two things helped it... but I scraped out ALL epoxy that was anywhere near the IAC valve, bore, seat, etc. I also enlarged the holes that were drilled using a small file set. I don't have the measurements of the inside diameter because I didn't have a set of drill bits handy to check them with. I also opened up the exit of the IAC hole that I drilled so it sort of created a chamber around the IAC plunger. This fixed the problem!
If I were to do this project again, I would do a couple of things differently: I would not use a Dremel to remove the ridge that's just in front of the TB blade, it takes too long even using the high speed cutter bits which is what worked fastest for me. Get a die grinder! Also, instead of filling the IAC cavity up with epoxy then reshaping it and drilling holes through it I would try to find a machine shop that could weld a small aluminum plate over the cavity instead, then drill a hole or three into that. They would need to weld it to the inside edges of the cavity though so the welds could be ground smooth to match the rest of the throttle body.
If you do use epoxy, I think I would try one of the "stick" epoxies that you have to knead to get it to ready instead of mixing it. I'm guessing it would be easier to work with. Other than that, just don't touch the edges of the blade or grind around the area where the blade rests when closed, and don't port the area behind the blade. It was very handy having a small Xacto file set around to work on the epoxy in areas where it was too small to use a Dremel. A set of dental picks/scrapers are good to have nearby too in case you get epoxy in the IAC area and need to remove it after the epoxy is set. It's a VERY small area to work in!
This is a good mod though! Don't forgot to do the throttle body bump stop mod, and adjust your throttle cable, and do the coolant bypass mod too!
If I were to do this project again, I would do a couple of things differently: I would not use a Dremel to remove the ridge that's just in front of the TB blade, it takes too long even using the high speed cutter bits which is what worked fastest for me. Get a die grinder! Also, instead of filling the IAC cavity up with epoxy then reshaping it and drilling holes through it I would try to find a machine shop that could weld a small aluminum plate over the cavity instead, then drill a hole or three into that. They would need to weld it to the inside edges of the cavity though so the welds could be ground smooth to match the rest of the throttle body.
If you do use epoxy, I think I would try one of the "stick" epoxies that you have to knead to get it to ready instead of mixing it. I'm guessing it would be easier to work with. Other than that, just don't touch the edges of the blade or grind around the area where the blade rests when closed, and don't port the area behind the blade. It was very handy having a small Xacto file set around to work on the epoxy in areas where it was too small to use a Dremel. A set of dental picks/scrapers are good to have nearby too in case you get epoxy in the IAC area and need to remove it after the epoxy is set. It's a VERY small area to work in!
This is a good mod though! Don't forgot to do the throttle body bump stop mod, and adjust your throttle cable, and do the coolant bypass mod too!
02-28-2004, 11:40 PM
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Originally Posted by Chili Pepper
Well, I'm not sure which of the two things helped it... but I scraped out ALL epoxy that was anywhere near the IAC valve, bore, seat, etc. I also enlarged the holes that were drilled using a small file set. I don't have the measurements of the inside diameter because I didn't have a set of drill bits handy to check them with. I also opened up the exit of the IAC hole that I drilled so it sort of created a chamber around the IAC plunger. This fixed the problem!
If I were to do this project again, I would do a couple of things differently: I would not use a Dremel to remove the ridge that's just in front of the TB blade, it takes too long even using the high speed cutter bits which is what worked fastest for me. Get a die grinder! Also, instead of filling the IAC cavity up with epoxy then reshaping it and drilling holes through it I would try to find a machine shop that could weld a small aluminum plate over the cavity instead, then drill a hole or three into that. They would need to weld it to the inside edges of the cavity though so the welds could be ground smooth to match the rest of the throttle body.
If you do use epoxy, I think I would try one of the "stick" epoxies that you have to knead to get it to ready instead of mixing it. I'm guessing it would be easier to work with. Other than that, just don't touch the edges of the blade or grind around the area where the blade rests when closed, and don't port the area behind the blade. It was very handy having a small Xacto file set around to work on the epoxy in areas where it was too small to use a Dremel. A set of dental picks/scrapers are good to have nearby too in case you get epoxy in the IAC area and need to remove it after the epoxy is set. It's a VERY small area to work in!
This is a good mod though! Don't forgot to do the throttle body bump stop mod, and adjust your throttle cable, and do the coolant bypass mod too!
If I were to do this project again, I would do a couple of things differently: I would not use a Dremel to remove the ridge that's just in front of the TB blade, it takes too long even using the high speed cutter bits which is what worked fastest for me. Get a die grinder! Also, instead of filling the IAC cavity up with epoxy then reshaping it and drilling holes through it I would try to find a machine shop that could weld a small aluminum plate over the cavity instead, then drill a hole or three into that. They would need to weld it to the inside edges of the cavity though so the welds could be ground smooth to match the rest of the throttle body.
If you do use epoxy, I think I would try one of the "stick" epoxies that you have to knead to get it to ready instead of mixing it. I'm guessing it would be easier to work with. Other than that, just don't touch the edges of the blade or grind around the area where the blade rests when closed, and don't port the area behind the blade. It was very handy having a small Xacto file set around to work on the epoxy in areas where it was too small to use a Dremel. A set of dental picks/scrapers are good to have nearby too in case you get epoxy in the IAC area and need to remove it after the epoxy is set. It's a VERY small area to work in!
This is a good mod though! Don't forgot to do the throttle body bump stop mod, and adjust your throttle cable, and do the coolant bypass mod too!
would not flow in there.( i coated the battery with free coat- really light oil
so the epoxy would not stick to the battery)
