Mechanics

TRUCK STARTS BUT SOMETIMES WHEN IDELING AT STOP IT SHUTS DOWN BUT RESTARTS, WHAT IS PROBLEM?

1995 GMC Sierra • 200,000 miles

I have done a tune up, plugs rotar wires air filter and fuel filter, seems to be still having same problem. Gas pedal seems to be sticking a little when trying t get going. I hae put injector cleaner in tank and also sprayed carb cleaner in carburator, with same problems occuring.
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Jsorr
September 4, 2011.



Also seems to be using more gas than usual.

Tiny
Jsorr
Sep 4, 2011.
It could be the Idle Air Control Valev, IACV, which adusts idle when load demands are changed on engine.
However, the fact that is is using more gas is usually indicitave of a failed O2 sensor. The O2 sensor is one of if not the most important part indeterming the air/fuel ratio. If it fails, it will either send a voltage signal to the ECU for chagnges in fuel management. They usally fail with the signal being for more fuel. Also, if you have anexhaust leak near an O2 snesor, it will think the mixtue is lean and tell the ECU more fuel is needed.
Try replacing the O2 sensor if it has never been replaced. With the age of the vehicle it would be a good idea anyway. Get some good injector cleaner. Most cleaners do not work well. There are only 2 that I reccomend; SEA FOAM or BG44K. You might have to go to a service station to get them and I would suggest getting 2 cans. They work so well you will need to change the oil afterwards from all the gunk it will clean out.

This is a common problem on all older cars and trucks. I have seen this many times before. The ingnition switch has a spring in it, that returns the ingnition switch from the start position to the on position. This spring gets weak with age and the spring does not return the ingnition all the way back to the on position. There is a dead spot between the start and on position on the ignition switch. All you got to do is after starting, turn the ingintion 1/4 inch more, back towards the on position. You can also replace the ingnition switch, but turning the switch back 1/4 inch back to the on position is free.

Tiny
James Himber
Sep 4, 2011.
If it is in between start and on have you ever seen one get stuck in the start position? Or, is is just off of the full turn of the key?
In this situation though the truck will run with starting fluid indicating a RUN position contact.
It is certainly worth trying and I would like to know what happens as I have never run across that before.
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Sorry I got the starting fluid situation backwards. I have another person I am helping who has same problem but starting fluid is helping.
Is there a lot of gunk around the Throttle Body intake butterfly? If so, it is made to have a gap to allow for idle and there are a few vacuum orifices that need to be cleaned out from the other direction. If these holes get plugged, it will affect idle, e.G. IACV. Does it have trouble starting when it is cold start?


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