1989 1500 5.7 head scratcher
 

Morning all,

I'm trying to figure out a little burp with this truck. For the last couple months the mileage has been really bad and when it starts the engine surges, almost like a vacuum leak until it runs for a few minutes. I crossed the terminals on the scan port and it flashed an O2 sensor, so I changed it and it's still doing the same thing. I was a bit suspicious about the sensor though, it was a light tan color, which tells me its not burning rich even though the thing is sucking the gas. I'm wondering if the cold temp sensor is gone which would throw off the O2 sensor? The weird thing I find though, once it's up to operation temp the service light doesn't come on right away. We drove it all over town for at least an hour and nothing, it only comes on going down the highway and only after about ten minutes. My recommendation to my girlfriend was to find a home for it as a soup can or tin roof, but she's in love with the old thing (what's left of it), so I have to fix it.

Thanks guys

Id try the temp switch.Does it surge on a hot start?

not on a hot start, only cold. that's what i'm guessing as well. i have to cross the port out again and see if it flashes that code now

did you replace the temp sensor?

not yet, that's my next step. The nice thing about these older trucks though, is the lack of sensors.