350 tbi idling

87k5

87k5

Well-Known Member
Joined
Mar 12, 2006
Location
Columbia SC
I appoligize if my wording is not the best, this is a first for me.
87 k5, 350 tbi bored 30 over
When I crank it up it idles fine for about 30 to 45 seconds then from idling it will lobe down and then back up and then down to the point where it just cuts off. Sometimes it will taks a while to get it started but sometines it will start right back up. Why will my engine not idle smoothly? People have suggested the o2 sensor and the fuel injectors.
 
Sounds to me like a MAP sensor. Just becuse it runs fine to start. I think the first few seconds after you start the engine it is in a open loop condition(defalt) until the engine gets going and starts to use the sensors for control. then when it trys to read the map it can't or the reading is wrong.
This is just a guess. but since most all of the map sensor are the same for all GM engines jsut barroe one from a buddy,plug it in and try it.:)
 
The change in idle is most likely something to do around fuel, Coil usely works or doesn't, liquid filled ones usally fail after they heat up, Dist. problems usally cause it to bust up. So I would go with the fuel mixture an its components as stated, this was the first year of Tbi on the trucks, so one of the sensors or fuel reg. is probally worn out if it has the factory components.
 
Thanks for the info. I do believe the componets are stock and I do have another truck I can switch out the old componets with.
 
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