High Idle! HELP!!

[Fireman5045]

Hey guys/gals! This is my first post here and I hope I'm in the right spot. I have a 98 Suburban K2500 with the 454 vortec. About a week ago it developed a very high idle. When u fire it up it immediately goes to 2500 rpms and stays there. Every once in a while it will try to idle back down then goes right back. So here is what I've done. I have cleaned the throttle body, MAF, and IAC. Then I sprayed starter fluid all over the engine compartment looking for vacuum leaks. None found. Then I replaced the IAC and tried every way I could find online to reset it. Then I replaced the TPS. No change. Then I replaced the MAF. No change. Replaced PCV valve. No change. I'm goin crazy here please help

 

[Jrgunn5150]

Have you visually verified that the throttle blade is closing? Have you looked at it at idle to see if engine vacuum is pulling it open?

 

[Fireman5045]

Yes. I pulled everything off down to the throttle body and it's closed all the way. All the air is being sucked in passed the IAC. With the diagnostics computer the IAC shows 0 counts which should mean fully closed but it's not closed. It's wide open

 

[Fireman5045]

I'm beginning to wonder if it's an ECU problem. Is there somewhere I can get a diagram of all the vacuum hoses on the truck so I can check every single one?

 

[Jrgunn5150]

Do you have a bad ground or chewed up wire there or anything like that?

 

[Fuzzy]

Have to tried disconnecting the IAC while the truck is running to see if there's any change in how it idles?

 

[Fireman5045]

I'm gonna ground it straight to the battery and see if it changes anything. And unplugging it doesn't change anything

 

[Zach Kramer]

Looks like your looking in the right direction possible that your not getting power to the iac valve it seems the ecu is comanding it closed but nothing is happening might have a broken wire to it