Hello, I have a 95 GMC Sierra 1500 4x4 with the 5.7 350, has 176,000 miles, the truck runs great except when at idle, both with it in gear and out of gear at idle, almost like its missing, but runs fine when above idle, I replaced the fuel pump about 800 miles ago because the truck would surge while driving, new pump all fine so I know this new problem cant be the pump, new fuel filter, air filter, I cleaned the egr valve figuring it was that, no difference, replaced the spark plugs, I also checked for air leaks around the throttle body and intake manifold and checked all vacuum lines, all fine, I do have a DT Code for the 02 sensor showing a lean exhaust but I dont think an 02 sensor could cause this, I have also noticed that if truck sits shut off for more then 5 min the restarted it idles smooth untill driven, what could this be? I am hopping I dont have low compression in one cylinder. Please help, thanks!
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/
Mine is not throwing any code and has TBI and it sounds like a bad misfire but when you go over 3000RPM she has all the power you need and sounds great. But won't start on it's own you have to push on the pedal witch is not right you should be able to just turn the key and she should fire right up?????
This is a very common problem for this truck .in your distributor you have a little electronic board the wires break but still make contact .you can change this or buy an differnt distributor. even a wrecker one. the key was you said the truck surges . very common . try this. it will work.
i said electronic board i meant the coil in the distributor the wires break but still make contactt
Hello guy and gals this model the 4.3 has IAC val;ve on the back on the throttle and a small this one the left side of the TBI the IAC this is big and on the back side of the TBI and there is no copde or check engine lights on It does smeel like exaust really bad under the hood I think this is a electric EGR right ? I am stumped the only thing I think I can do is take off the electric EGR valve and see what going on with it. When took the power clip off the back it threw a check engine light but went away after I turned the key off then back on. So I am lost any photos or help would be great. Thank you for your time. Eric
Hey whated to say it was the electric EGR valve got it off and it was stuck wide open. Soaked it with carb spray and cleaned it up and the 4.3 runs like new that way it did the other day. But while doing all this work the water pump went out !@#$#@! so I have to wait for pay day and buy a new one. I hope this helps some body.
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SOURCE: random/multiple cylinder misfire detected Bank 1
Hi
it sounds like the EGR valve is either dirty or has failed, do you lose any power at all, if not then thats a good sign, remove the EGR and clean with carb clneaer only, leave to dry naturally and dont try to dry it or touch it yourself, they often do get dirty as the job they do is similar to that of a turbo with exhaust gasses.
Hope this helps
Regards
Dan
lastly clean the air mass sensor too, both are easy to do and easy to remove.
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