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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: Tazman on August 23, 2010, 07:42:42 am

Title: Surging Idle
Post by: Tazman on August 23, 2010, 07:42:42 am

I have an issue with my truck when it is first started in the morning.It starts fine and after a few seconds the idle fluctuates or surges between normal and low.I have been told it could be the TPS but have checked it and that is fine.Also have been told it could be vacuum which I think it is but can not find a leak any where.I have been looking for a link or site that would show the complete vacuum line diagram for the truck.Any one know where I can find that?Thanks

Title: Re: Surging Idle
Post by: Irish_Alley on August 23, 2010, 09:42:30 am

There's a rubber fuel line in the tank. It can and will crack not causing a leak on the outside but its in the tank. Will cause a rough idle running like crap. The line is in the package with a new pump. But I think you can just replace it with fuel injection line

Title: Re: Surging Idle
Post by: bake74 on August 23, 2010, 03:22:19 pm

  If you have an inline fuel filter, did you think to change it.  Filters when they start to get dirty will flow fuel normal at first, then as fuel flow through it they plug up.  Then after sitting the clog settles and when you start it up the clog can start all over again.   Tom 

Title: Re: Surging Idle
Post by: Lt.Del on August 23, 2010, 04:08:41 pm

the IAC may be malfuntioning.  That is the idle air control valve which opens and closes to allow air to come in from throttle body.


http://www.youtube.com/watch?v=oNO8GCN8jQA&feature=related


http://www.google.com/imgres?imgurl=http://shbox.com/1/iac3.jpg&imgrefurl=http://shbox.com/1/component_location_views.html&h=607&w=792&sz=108&tbnid=K-Lk5VOQ2AdFkM:&tbnh=110&tbnw=143&prev=/images%3Fq%3Didle%2Bair%2Bcontrol%2Bvalve&zoom=1&hl=en&usg=__4oX6yvWoQusrUo2bf3sfP_x98gs=&sa=X&ei=JuNyTJflNMGB8gbwvpWPBA&ved=0CDwQ9QEwBQ

http://www.youtube.com/watch?v=tUkCCwqU3eU

http://www.youtube.com/watch?v=W_a01sHy3qo&feature=related

Title: Re: Surging Idle
Post by: Tazman on August 24, 2010, 07:47:11 am

I change the in line filter every year some times more.The IAC valve ,is there a way to test it?Thanks

Title: Re: Surging Idle
Post by: Lt.Del on August 24, 2010, 11:57:02 am

http://www.youtube.com/watch?v=406BTo4JE3A

Title: Re: Surging Idle
Post by: VileZambonie on August 24, 2010, 09:43:33 pm

If you don't have access to a scan tool, spray some carb clean at the base of the tbi unit and see if it changes the way the engine runs.

Title: Re: Surging Idle
Post by: Tazman on August 25, 2010, 08:30:20 am

I did that some time ago.Is there a way to find out where every vacuum line is in that truck?Thanks

Title: Re: Surging Idle
Post by: Captkaos on August 25, 2010, 04:23:51 pm

There aren't that many on a TBI.
PCV, EGR and Purge at the front and MAP and Booster at the back if I remember correctly.

Title: Re: Surging Idle
Post by: Tazman on August 30, 2010, 08:25:23 am

Did a double check yesterday found nothing.Pulled the EGR valve,cleaned it and reinstalled it.Ran better this morning but the check engine light came on as I was going to work.Will check with code reader later.I think I should have left things alone.Thanks