Question about 1994 GMC Sierra

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Runs extremly rough at idle runs great at speed

Runs extremly rough at idle .runs great at speed or under load 1994 5.7l tbi Has new cam ,lifters ,distr, plugs and wires

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  • haloplmbr7 Jun 25, 2009

    yes timing is good and all parts are stock no mods.will try the idle censor next. And i also heard that a sticky or bad egr valve may cause the same results

  • haloplmbr7 Jun 25, 2009

    no codes or check lights of any kind

  • yadayada
    yadayada May 11, 2010

    any trouble codes???

  • chrisbock May 11, 2010

    is this all you have done. and is the cam bigger than original

  • yadayada
    yadayada May 11, 2010

    ANY TROUBLE CODES?

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Change fuel regulator and upper plenum gasket I had same problem with my 96 Gmc 5.7lt threw a bunch of parts at it costing hundreds I finely broke down pulled top plenum about a 3 hr job cost 60 bucks runs like a raped ape now hope this helps

Posted on Apr 21, 2012

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Have you checked the pcv valve. a vacuume leak will make your car idel rough too listen arround the throttle body and intake hose for a hiss use a piece of hose @ 2 feet long 1 end in ear other end prod arround to listen for a hissing sound if you hear one plug it up if idle gets better that hose or hole need to be connected to what ever it came off of.

Posted on Jun 26, 2009

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Did you get the timing right?
Listen for air leaks around throttle body base.

Posted on Jun 24, 2009

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IDLE POSITION CENSOR IT IS ON THE OUTSIDE ONTHE SIDE OF YOUR TBI DISCONNECT THE WIRING IF THE IDLE SMOOTHS OUT IT IS YOUR PROBLEM IF YOU LEAVE IT UNPLUGED IT WILL RUN FINE BUT YOU WILL HAVE A CHECK ENGINE LIGHT

Posted on Jun 24, 2009

  • alex MACHELL Jun 26, 2009

    yes the egr can do that i have a bad egr on my 99 gmc envoy and the only thing it is doing is my service engine soon light is on also you could have a bad o2 sensor i have seen that do what yours is doing and there if you unplug it and it smooths out thats your problem the o2 sensor is in your exhaust pipe right in front of you catalytic converter and will have a two wire plug going to it

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I have a 1988 5.7 gmc that after start up idles fine runs stromg under full throttle but at highway speed and under no load speed it sputters and at slow speed it is running rich i have done complete...


I have a 1988 5.7 gmc that after start up idles fine runs strong under full throttle but at highway speed and under no load speed it sputters and at slow speed it is running rich i have done complete tune up rebuilt the tbi One concern i have is someone removed stock air cleaner system and the one they installed has no intake air sensor could this be the problem ?
IT CERTAINLY CAN BE THE PROBLEM. The air flow sensor if a VITAL part of your fuel delivery and emmision's system. Your mixture is controlled by a computer that uses the sensor data from that device. If you possibly can get the old one, put it back on. It is possible that I may not be totally right about this point but the operation of your engine is dependent on all the parts being there.
and also i have no codes and no ck engine light on.
There may not be code for a missing part. That system is not perfect.
I hope this helps,
Happy New Year,
Mark

Jan 03, 2011 | 1988 GMC C1500

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****** ignition timing....this will lower HC but raise other values during test.
Do you have room to increase other values?
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