Help 94 Sierra

Morland · October 6, 2014

Hello,

I have a 94 GMC Sierra that I got from someone in fair condition and it has around 160,000 miles on it. For some reason when I start it idles rough and the smell of gas comes out the tail pipes not only does this happen on cold starts but almost everytime I cut the truck off and go to cut it back on. Ive done a complete tune up on the truck and ive replaced the idle control sensor. for me to get it to idle correctly I have to either press down the gas peddle for a few seconds to the floor and then start it or I pump the gas peddle about ten times and then I get a correct start. Every blue moon the idle will get so low that it will cut off in traffic and some times if I pull up to a stop sign it will go back to sputtering if I stump the gas. The timing seems to be correct and the firing order is correct. The only thing that im aware of on the truck is currently there are aftermartket headers on it they appear to be on correct but it looks like the header to collector gasket is not on. Also, the gentlemen that I purchased the truck from has banged the cadlistyic converter to get all the stuff out. Since there is no header to collector gasket on their could that make my truck do the rough idle? You can hear excuast leaking out there just before the O2 sensors. Im in need of help here.

-Thanks.

darkfox1 · October 6, 2014

I'm going out on a limb here, but I'm wondering, on my 88 gmc I had 2 injectors mounted on top of the TB, with the intake filter off you could see the gasoline spraying in.

My problem was 2 fold on that truck (well on THAT heap it was 10 fold but.. to get it running..) 1. A backfire had caused the injector wires to be burned/melted and sometimes they would arc, and 2. My injectors were clogged/old/bad.

I grabbed new wires from a caprice in the junkyard and bought 2 new injectors and it fired right up.

My thought is, take a look at your injectors, pull the cable, see if they spray right, could be that they are not in optimum operating condition?

If you had a bad O2 sensor or reading, that can also cause rough idle. You can test by disconnecting the o2 sensor harness and see if the idle changes. If it gets worse then its reading *something* at least. I wouldn't think an exhaust leak would cause a bad idle though.