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TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

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Old 04-18-2009, 03:22 PM   #1
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305 TBI 1991 runs rough!

Hey guys, After driving my Firebird around today for around half an hour, and then turning it off for 30 minutes, then driving more, when I had fired it up the 2nd time, it revved up to 1500 RPM, then dropped down to 300 and ran like it had a huge cam. What could cause this?
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Old 04-18-2009, 08:50 PM   #2
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Re: 305 TBI 1991 runs rough!

I put in some higher octane gas, didn't seem to make a difference.. No one? Not a word?
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Old 04-18-2009, 09:03 PM   #3
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Re: 305 TBI 1991 runs rough!

Sounds like your IAC.
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Old 04-18-2009, 10:32 PM   #4
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Re: 305 TBI 1991 runs rough!

Crappy Windsor air??? Sorry man idk, I just noticed we're from the same town is all.
Good Luck brother.
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Old 04-18-2009, 10:40 PM   #5
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Re: 305 TBI 1991 runs rough!

Check fuel spray coming from your injectors - should be a nice cone hitting throttle walls. If you see any large drops - start checking fuel pressure.

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Old 04-19-2009, 11:21 AM   #6
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Re: 305 TBI 1991 runs rough!

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Crappy Windsor air??? Sorry man idk, I just noticed we're from the same town is all.
Good Luck brother.
Thats probably the problem, too.. I'll Take out the IAC and clean it, I know on my last car that was a problem..

I think I've seen your car before Dubzz, looks familiar.
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Old 04-19-2009, 12:58 PM   #7
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Re: 305 TBI 1991 runs rough!

Remember to clean inside the throttle body.
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Old 04-19-2009, 07:31 PM   #8
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Re: 305 TBI 1991 runs rough!

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Thats probably the problem, too.. I'll Take out the IAC and clean it, I know on my last car that was a problem..

I think I've seen your car before Dubzz, looks familiar.
I just picked it up a few months ago. Im the 3rd owner. Its in its 3rd generation now....Ill fix er up nice. It needs some work but runs decent. Haha...everyone calls me Dubz

Hope you get yours running better.....the info here is invaluable.
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Old 04-19-2009, 07:40 PM   #9
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Re: 305 TBI 1991 runs rough!

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Remember to clean inside the throttle body.
I cleaned it out when I first brought the car home, made a hell of a difference. It still looks pretty clean, though. I never took apart the IAC, just the EGR.

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I just picked it up a few months ago. Im the 3rd owner. Its in its 3rd generation now....Ill fix er up nice. It needs some work but runs decent. Haha...everyone calls me Dubz

Hope you get yours running better.....the info here is invaluable.
Yea I've been hanging around here a while, where in Windsor you from? I normally stick to LaSalle, it's where I went to school..
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Old 04-19-2009, 10:29 PM   #10
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Re: 305 TBI 1991 runs rough!

I grew up Central East Side....maybe you could help me along around here sometimes.
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Old 04-19-2009, 11:25 PM   #11
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Re: 305 TBI 1991 runs rough!

You don't take apart the IAC, you just get a new one for $30-$60, depending on who you buy it from.
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Old 04-20-2009, 01:05 AM   #12
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Re: 305 TBI 1991 runs rough!

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You don't take apart the IAC, you just get a new one for $30-$60, depending on who you buy it from.
I'd rather just clean it and spend the money elsewhere.

It's easy to take the IAC apart and clean it. I had the same thing going on with mine and after cleaning it idles like it should.
1. Disconnect the IAC and then remove it from the throttle body.
2. Plug the connector back into the IAC and wrap the IAC up in a rag.
3. Under the dash jump terminals A & B on the ALDL port and turn the ignition to run but don't start the engine. This will cause the IAC to push the pintle all the way out. Let the IAC run for about 30 seconds then turn the switch to off.
4. Disconnect the IAC from the connector being careful not to drop parts.
5. In the rag you should have the IAC connector/motor, pintle and spring. Clean all the carbon, oil and junk from the parts with and old tooth brush and some tbi/carb cleaner. Hold the IAC motor upside down and spray a little into the hold the pintle goes into and then shake the excess out. Do this one or two times to make sure the gunk is out.
6. Put a little light oil onto the threads to the pintle and reassemble IAC. On mine I put the spring on and then held it down with my finger and screwed the pintle all the way in. It's important that the pintle be in the fully retracted position.
7. Spray some of the tbi/carb cleaner into the IAC hole in the throttle body and make sure it is clean and free of any carbon or junk.
8. Install the IAC back into the throttle body and reconnect the connector
9. Under the dash jump terminals A & B on the ALDL port again and turn the ignition to the run position but don't start the engine. This will cause the IAC to extend the the pintle to the fully closed position in the throttle body. Let the IAC run for about 45 seconds then turn the switch to off.
10. Remove the jumper from the ALDL.
11. Start the car and the computer should adjust the IAC for the proper idle.
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Old 04-20-2009, 06:36 AM   #13
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Re: 305 TBI 1991 runs rough!

Thanks Jason, I'll do that tonight.
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Old 04-20-2009, 08:20 AM   #14
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Re: 305 TBI 1991 runs rough!

I didn't think could because I thought all sold today the pintle was in a permanent position.
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Old 04-20-2009, 06:40 PM   #15
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Re: 305 TBI 1991 runs rough!

I took it all apart and cleaned it, ran like hell for about.. 4 or 5 minutes and then it started to idle nicer, around 600 RPM. Now if only the weather could improve so I can do a road test..
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Old 04-20-2009, 07:20 PM   #16
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Re: 305 TBI 1991 runs rough!

I forgot to add, the left injector really had a heavy spray, it made a wierd noise, too like a hissing. The right side seemed ok. I think I have to get a rebuild kit, any suggestions?
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Old 04-20-2009, 07:47 PM   #17
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Re: 305 TBI 1991 runs rough!

I just had mine serviced for $18 an injector.
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Old 04-20-2009, 07:50 PM   #18
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Re: 305 TBI 1991 runs rough!

An easy way to check the spray pattern is to shine a timing light at the TBI while the car is running. If the spray pattern is not a cone shape that hits the walls of the throttle body evenly then a rebuilt kit probably won't fix the problem. The injector/injectors probably need to be cleaned in addition to the the TBI being cleaned and rebuilt. Any of the local parts stores should have a rebuild kit.
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Old 04-20-2009, 09:05 PM   #19
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Re: 305 TBI 1991 runs rough!

Quote:
Originally Posted by Jason89RS View Post
An easy way to check the spray pattern is to shine a timing light at the TBI while the car is running. If the spray pattern is not a cone shape that hits the walls of the throttle body evenly then a rebuilt kit probably won't fix the problem. The injector/injectors probably need to be cleaned in addition to the the TBI being cleaned and rebuilt. Any of the local parts stores should have a rebuild kit.
I got in there with my mag light and it looked like a lot was being sprayed on one side of the butterfly.
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Old 04-29-2009, 01:10 AM   #20
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Re: 305 TBI 1991 runs rough!

That injector probably needs to be cleaned or replaced. What did you end up doing and did resetting the IAC solve your idle issues?
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Old 04-29-2009, 01:10 AM
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