Hi.
My 1994 GMC Sierra 1500 has a 5.7L V8. It has ALWAYS run tip top. About 2 days ago it started to idle horribly. When it idles it runs like a high displacement engine would with a big cam. I pulled that cap and rotor and they were shot so I replaced them. I also replaced the fuel filter and air filter. I put new plugs in as well.

It runs GREAT under a load when rolling down the road which leads me away from a miss like bad plug wires. But man it idles horrendously around 350-400RPM's. Sometimes it jumps up like its going to come out of it then starts idling rough again.

There is NO check engine light on.

Any Ideas?

 

hey, i have a 97 sierra and well the same problem was happening w/ me. My mechanic told me it was what mechanics call the spider. its looks like a spider and it dumps to much fuel into ur engine which makes it run like poop. It cost me, for my mechanic to do it 800 dollars, but now that i got it done my truck runs fine.

 

That's odd. I've been wrenching on cars all my life and never heard of the *spider*. I do believe it is getting too much fuel dumped in for sure. Anyone else care to add?

 

i would start by cleaning out the throttlebody with some carb and choke cleaner and then check 4 vacuum leaks

 

The spider he refers to is the fuel inj assembly on a Vortec...You have TBI..anyway...

Runs great down the highway but slobbers at idle?..Your egr valve is hung open....with it idling,smack it with a hammer and see if she returns.You can feel under there to see if its stuck...but they got hot!

 

I was leaning toward the EGR valve. It rarely acts up now but when it does it is annoying. Thanks.

 

get him healed?

 

Ahh, this one I know. I had the same problem, but mine would leave me setting. The sensor is located in front of the TBI on the manifold, right beside the water inlet. When you replace it, make sure you get the plug too, because the new sensor does not fit the plug, $8 should get you back up and running smooth. Anyone know where the diagram is located for a 1994 GMC? My gauges ran my battery dead!

 

Duplicate post sorry>

 

What sensor are you speaking of?