So, aside from my AC vent problems my blazer has been running good since I changed the spider/nutkit out. I went and fired it up this morning, immediate high idle + check engine light. I tried to read the code but all I get is code 12, which is the same as no code. It rained all night long but the engine bay looks dry. IAC, MAP sensor, egr valve, speed sensor..all less than 2 weeks old.

Any ideas?

 

So I let it idle for an hour or so, and shut it off. Tried to run code, still nothing. Truck was still not completely warm, let it run another 45 min, shut it off for a hour. Idle was still high. Fired it up the hour later and it ran like it was fine, no CEL and normal idle.

Weird huh?

 

Since nobody has replied I will post another update of the symptoms. Yesterday the truck ran fine all day. I work nights, so I go to fire the truck up at 9pm to go to work and it immediately idles too high and CEL comes on. I drove it to work and noticed transmission popped into gears very roughly (might have just been higher idle?) and the brakes seemed to work better than they should. I got to work (3 miles away) truck was still cold, idling high. I let it sit outside running for 20 min and came back outside, still idling high, still CEL. I shut it off and started it right back up...ran like a champ, perfect idle, no CEL?

Any ideas? Checked all vacuum lines and its got a new egr and I checked to see if something was stuck in it a few minutes ago. IAC is new and I pulled it off to see if it looks dirty and it looks brand new. PCV Valve is also new as well as 90% of the exterior of the motor less than 2 months old. Something electrical? Please somebody give me an idea of a potential culprit.

 

#1 thing, have you ever thought to check what the computer is telling you is wrong? That would be a place to start. Its possible there is a loose ground somewhere that is affecting a sensor or two. Intermittent problems like this are generally due to faulty wiring.

 

Heres another update....it ONLY does this when its cold. As soon as it warms up, turn it off, turn it back on and it runs like a champ. In nuetral the idle is extremely erratic. When you put it in drive it SNAPS into gear and chirps the tires. It wont shift into 3rd gear...period, wont do it until it warms up and you restart it. The brakes are so sensative when you try to stop fast the rear ones lock up and slide. While driving it will sort of "burp" and the rpms will drop and then come back up. It idles extremely high, you dont even have to hit the gas to take off, just let go of the brakes, sometimes when you go to take off, you let off the brake and hit the gas and it almost stalls because the rpms drop for a second, then it takes off like crazy.

I have:
Pulled EGR out and cleaned it.
Swapped new IAC for another new one
Checked for loose ground wires
Swapped out ECU
Checked for vacuum leak
pulled off a few things and checked for other problems.

any ideas?

 

And still no DTCs from the computer??? If the light is on there should be stored codes... Sounds like you've got a whole host of issues...

Have you removed and cleaned all of the grounds that you can find?

 

Checked and cleaned all grounds. Battery has ground kit, checked it as well. Motor runs for over 10 minutes, but DTC does not store, nothing is read but code 12. ?????

 

If it returns to normal after it's warmed up... could be an intake or throttle body gasket...

Also, check your IAC, and make sure it's working properly...

 

 

Check and make sure the IAC is getting proper voltages...