My truck starts up, idles fine for a few seconds and then revs itself up to about 1500 rpm and while that happens the CEL flashes 4 times then stops. A little later the engine either returns to its normal idle (around 700) OR to the point of almost stalling. After searching online for hours I found someone who had the same issue and they had a thread on a forum a few years back. What I've gotten so far is some others mentioning their o2 sensor harness was bad and if I unplugged the only 15 amp fuse in the distribution box and it doesnt have those problems when starting up then its the harness. My truck starts up better with that fuse unplugged. I checked the harness visually and it seems ok. My question is if the sensor is bad would that fuse give me the same results?

 

Is this a V8? That actually sounds like somebody's put it in a KOER test mode. Have you looked to see if the connector pins are jumpered?

 

Sorry yes its a V8. 5.0...... Which connector pins?

 

Read the article at the top of this forum about reading OBD I trouble codes. If somebody put a jumper wire in to start that test and then left it in there, you'd get a 4 CEL burst a few seconds after startup telling you that it was an 8 cylinder engine.

 

Ok I'll look into that. While I have your attention maybe you can answer this other question. When looking at the engine from drivers side, below the fuel lines kinda level with the injectors theres what appears to be a place to plug something it, its got the diameter of dime or maybe a lil bigger, two pins inside there and nothing plugged into it. Not sure if thats for some sort of testing plug or if its missing something

 

Can you post a picture? Also, go into the control panel on here and edit your signature with your truck info (year, engine, trans, etc) so we know what you're describing anytime you post.

 

What you're looking for is a jumper wire between STI self test input and the main connector body as illustrated in the top right of this image.

 

Ok I looked and theres no jumper between those

 

Hmm... I'd go ahead and just step through that thread and start with the KOEO codes then.

 

Kinda hard to see but its pretty much right below where that thing is that looks like a tire stem.