Ported Throttle Body , Cold Start High Idle
Thread Starter
Instructor
Joined: Dec 2000
Posts: 135
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From: West Sand Lake N.Y. ny
Ported Throttle Body , Cold Start High Idle
Changed the throttle body to a ported G.M. unit bought from a fellow forum member. When I start the car up the tach jumps to 2,000-2,300 rpm and slowly goes back to correct idle of about 800. I had read about the fix for this but can't find it.( sonething about drilling a hole in the butterfly). I have put about 70 miles on the car since install and it only does it on a cold start. Every warm / hot start results in perfect idle. Any ideas? Thanks in advance. Ben :confused:
Melting Slicks
Joined: Feb 2001
Posts: 3,376
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From: Hershey, PA, USA
Cruise-In VI Veteran
St. Jude Donor '12
Re: Ported Throttle Body , Cold Start High Idle (BENSC5)
tyr an idle relearn
here's how.....
Just remember to do a idle relearn. Turn the key on but don't star the engine. Remove the number 16 & 23 fuses from the underhood fuse box. Turn the key off. Replace the number 16 & 23 fuses. Start the car and let it run @ 175 degrees or warmer for 5 minutes. Shut down the engine for at least 30 seconds, then drive the car for about 30 miles at varying speeds. If you do this kind of low bugget mods you will feel a big difference in the seat of your pants, and ET's. Good luck have fun.
here's how.....
Just remember to do a idle relearn. Turn the key on but don't star the engine. Remove the number 16 & 23 fuses from the underhood fuse box. Turn the key off. Replace the number 16 & 23 fuses. Start the car and let it run @ 175 degrees or warmer for 5 minutes. Shut down the engine for at least 30 seconds, then drive the car for about 30 miles at varying speeds. If you do this kind of low bugget mods you will feel a big difference in the seat of your pants, and ET's. Good luck have fun.
Melting Slicks
Joined: May 2003
Posts: 2,851
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From: San Bruno Ca
Re: Ported Throttle Body , Cold Start High Idle (BENSC5)
I just ported my TB last week and it idles perfectly. If your car jumps up hi on idle when you first start it, and then starts to go down...this means something is not right, but the computer has slowly compensated for it. You need to get it fixed. I am guessing the inside of the TB you just installed is epoxied in the front of the "bell mouth". there should be a hole drilled approximately 3/8" in dia. in the epoxy. I don't know if this will fix the problem, but it could be the cause.
good luck
good luck
Melting Slicks
Joined: Aug 1999
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From: Milwaukee WI
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Re: Ported Throttle Body , Cold Start High Idle (BENSC5)
Chances are your throttle body is flowing a significant amount more air at idle than it used to.. The PCM "expects" a certain amount of air to be required , and thus a certain blade position, to get idle to a certain spot.. This is where the PCM will START to put the idle.. However, the extra air going in, that the PCM isnt expecting, will raise your idle. The closed loop feature of the PCM will eventually deal with the high idle, and bring it down. Although a relearn MAY solve the issue, I doubt it. The answer is programming the IAC park and running airflow parameters in the PCM..
Do NOT drill a hole.. the high idle indicates you already have too much air..
The epoxied hole, if you have done that, is not the issue... that is simply a place for the engine to obtain clean, filtered makeup air to replace what the PCV system takes out..
Just my 2 cents... Best Regards.. :seeya
Do NOT drill a hole.. the high idle indicates you already have too much air..
The epoxied hole, if you have done that, is not the issue... that is simply a place for the engine to obtain clean, filtered makeup air to replace what the PCV system takes out..
Just my 2 cents... Best Regards.. :seeya
Thread Starter
Instructor
Joined: Dec 2000
Posts: 135
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From: West Sand Lake N.Y. ny
Re: Ported Throttle Body , Cold Start High Idle (nevrenuf)
Thank you all for the insight. There is no epoxy in this unit. I believe a relearn is in order. This late fall I intend to have the car dyno tuned, that will smooth things out a bit I hope. AND find a few ponies..... :cheers: Ben
