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73-87 Chevy _ GMC Trucks => Performance => Topic started by: Tazman on January 19, 2011, 07:06:12 am

Title: Vacuum leaks ?
Post by: Tazman on January 19, 2011, 07:06:12 am

If an engine is idling fine one minute and then is not the next can it be a vacuum leak ?I have changed and or tested most everything concerning the idle in the past few weeks and it runs great mostly but once in awhile it still has that uneven idle.Any ideas?Thanks

Title: Re: Vacuum leaks ?
Post by: Irish_Alley on January 19, 2011, 08:14:25 am

Does it change like every second or more like its ok then you drive then stop and now its not ok

Title: Re: Vacuum leaks ?
Post by: Tazman on January 19, 2011, 09:37:41 am

It can be running great and I can come to a stop and it will start doing it.Or I can start it and it will idle fine but the next time it could be surging or uneven as soon as it starts.

Title: Re: Vacuum leaks ?
Post by: jaredts on January 19, 2011, 09:42:59 am

Do you have an old carb.?  If so a thorough cleaning with carb. cleaner can sometimes fix that.

Title: Re: Vacuum leaks ?
Post by: Tazman on January 19, 2011, 01:03:46 pm

No it is TBI and it is clean.Thanks

Title: Re: Vacuum leaks ?
Post by: Captkaos on January 19, 2011, 01:05:47 pm

have you checked your fuel pressure?

Title: Re: Vacuum leaks ?
Post by: Tazman on January 20, 2011, 08:26:54 am

Yes it was low,traced it to the fuel pump and replaced it two weeks ago.Thanks

Title: Re: Vacuum leaks ?
Post by: Irish_Alley on January 20, 2011, 05:15:22 pm

Sounds like a sensor problem more than vacuum problem

Title: Re: Vacuum leaks ?
Post by: Tazman on January 21, 2011, 07:09:49 am

The TPS ,oxygen and coolant sensors have been changed.Any idea which sensor could be the problem?Thanks

Title: Re: Vacuum leaks ?
Post by: Irish_Alley on January 21, 2011, 09:34:14 am

Do any of your other gauges fluctuate while its idling low

Title: Re: Vacuum leaks ?
Post by: Tazman on January 21, 2011, 11:31:38 am

Yes this morning with the lights on I noticed the volt meter fluctuating.Could the alternator be an issue?Thanks

Title: Re: Vacuum leaks ?
Post by: jaredts on January 21, 2011, 03:28:31 pm

The volt meter will fluctuate if your idle is going too low.  Do a little research on the idle air control valve.  From my very limited experience I believe your symptoms match a bad IAC.

Title: Re: Vacuum leaks ?
Post by: Irish_Alley on January 21, 2011, 06:03:31 pm

My 94 was kind of doing the same thing. Chtanged the alternator and noticed my ground to my bat was not even hand tight. Well between the alt and ground the problem was fixed. It would idle good sometimes the alt seamed to stop charging and it volts would be below 12 lights would dim and the rpm would drop almost seamed like it would die then I could take off and it would fix itself

Title: Re: Vacuum leaks ?
Post by: Tazman on January 23, 2011, 10:34:59 am

I changed the IAC a month ago I hope it's not bad.Went to Autozone and had the alternator checked which was fine.I am starting to wonder about the EGR valve,yet not everything points to that.I will check the connections to the alternator in the mean time.Thanks

Title: Re: Vacuum leaks ?
Post by: Irish_Alley on January 23, 2011, 01:07:58 pm

Well if the alt was bad and you didn't have the problem all the time. If it’s working fine when you test it will pass. Don’t think egr would do it since if it was bad it would be bad all the time not once in a while. Usually the only things that are good one minute then bad the next are electrical i.e.. Sensor or bad grnd. not just the connection to the alt but the battery and alt bracket

Title: Re: Vacuum leaks ?
Post by: Tazman on January 23, 2011, 08:55:26 pm

Thanks, I will keep checking.