Bought the truck last year to tow our boat. Earlier this spring it started to hesitate while driving and now it surges at idle and hesitates while driving. I have changed, air filter, wires, spark plugs, cap, rotor, EGR, PCV and IAC. The previous owner had the head gaskets replaced a few months before we bought it and replaced the fuel pump. I also replaced the fuel filter and had the injectors cleaned, pressure is up to spec. It does get better if you drive it for a while and then let it sit for 20 mins, then it runs pretty good, although there is some slight hesitation. I'm beginning to think maybe there is a vacuum leak because it gets better if the engine warms up then sits.
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SOURCE: hesitation
Remove the vaccume line to the EGR valve and see if it still does it. It may be a bad EGR valve.
SOURCE: 95 GMC hesitation
By "OVERDRIVE '' . are you meaning the TCC ( torque converter clutch ) is engaged ? and if so, when you increase RPM's to accelerate, it should disengage otherwise causing a noticeable hesitation. Hope this helps
SOURCE: my son's gmc 4.3l hesitates upon acceleration. I
do you have any check engine lights on? If you do, that is the first thing I would have checked. It does sound like plugged EGR, vacuum leak, or bad TPS
SOURCE: 94 suburban 350 will not idle..either low or
checkout the plantum gasket give these websites www.alldatadiy.com and www.autozone.com if all fails stop by your local library and get your hands on a Haynes auto repair manual for your SUV also would like to give you this information if you every have a hard to find GM-part they sells only GM its Schram auto & truck 1-800-292-1032 and the website is www.schramauto.com wish you the best of luck Michigan Man.
SOURCE: 95 GMC Sierra 4x4 350 5.7 rough idle problem
It sounds like a MAP sensor going bad. MAP is short for manifold absolute pressure sensor, it senses the manifold pressure and applies the right amount of gas with the right amount of ignition timing so the car runs and performs well if this does not work properly. It throws off the whole loop cycle for the computer, which in turn makes it run badly and get poor fuel economy. It can causes the engine to have a lack of power, combined with a loss of fuel economy. Poor take offs and sometimes an occasional stalling may occur if the MAP sensor is faulty and sending the wrong signals to the ECM.
Hope this helps and thank you for using Fixya.
Here is a link that my help you in the future.
http://www.troublecodes.net/GM/
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Is there any consumption of coolant or oil? Why did they replace the head gaskets and/or fuel pump? Has it ever ran well since you've had it?
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