Engine Performance problem
1990 Chevy Lumina 6 cyl Front Wheel Drive Automatic 157000 miles
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My service engine light comes on after it is warmed up. My gas mileage went down bad. I acts like it wants to die when I am at a stop light. It also acts like its cutting out. We replaced the coils and checks fluids. We are now thinking that it might be the Oxygen sensor. Please help before I go broke replacing parts.

if you dont want to go broke then get to the nearest autozone and have them scan the computer and post back the code so i can tell you what is wrong and what to replace.

they will scan for free!

autozone wont scan a 90. you'll have to jump pin a and b in the diagnostic center.
there are several posts on here that explain how to do it. then post the codes here and we'll tell you what they are...

they scanned my 87 :O have a nice little tool that hooks up to it

autozone nor pepboys would scan my 92. i had to use the good ol paperclip...

same purpose, find your dlc connector, the upper right hand corner the two in the upright hand corners are a and b, put a clip in, turn ignition and the check light will flash out.

as dna says.

do a search on the forums here and you will find lots about it.