High idle 6.0 in van.

[kensz28]

So I have a 2004 Chevrolet Express cutaway van that is my work vehicle and it has the six liter engine in it. Everything's been fine until I changed idle air control valve and the throttle position sensor a week ago. The reason that I change these parts is after a full tune-up and several throttle body cleaning it would stumble and stall and one time in traffic it died coming to a four-way stop but I nearly rear-ended the person in front of me because I had no power brakes. It's been smoked tested there's no leaks intake gaskets knock sensors harness all that stuff has been changed but now when I start it in the morning and idles at about 2,000 RPM and sometimes it comes down and sometimes it doesn't. I have disconnected the battery overnight and was told that it will re
learn but I'm just lost sometimes it'll hold 30 miles an hour going down the road all by itself.

[kensz28]

I should also stress there are no cel or ses lights or codes saved or pending. Stupidest thing I've ever seen

[SMWS6TA]

MAF - these need cleaning as much as when you change your air filter. Good practice is when you do the filter do the MAF.

Is the IAT connected as well?

[kensz28]

Maf has been cleaned recently. Correctly too. All sensors are plugged in. I thought there was a relearn procedure for IAC. Am I wrong? Or are there differences in 4.8/5.4/6.0 IAC?

[SMWS6TA]

Not for the IAC but there is for the TPS.

Check the IAC again, pull it off the throttle body and have someone turn the key, it should slide in and out. If it doesn't then it has a problem.

[kensz28]

Assuming all else is fine, what are the chances the new IAC is just no good? Two mechanics said its possible. The pintle on the new one was retracted as it should be since no voltage had been applied yet until it was installed. Could it be just junk??

[kensz28]

Not for the IAC but there is for the TPS.

Check the IAC again, pull it off the throttle body and have someone turn the key, it should slide in and out. If it doesn't then it has a problem.

I didn't know that. I'll do it after work. Sounds logical. That's

[kensz28]

So after I posted the van began running really well and had been since. So I'm assuming the IAC was able to calibrate itself. Now Monday the battery died cause the radio was left on over the weekend by mistake and now its idling really high again. I put the charger on overnight so nothing was disconnected. Should I disconnect the battery? And start over?

[SMWS6TA]

Sometimes if the ecm detects a low charge from the alternator it will go into limp mode and cause the engine to high idle. Usually around 3000 rpms.

You may want to get it both battery and alternator tested. If both check out ok look at the thin wire coming off the alternator next. If it's damage it will give a bad reading to the ecm. It tells the ecm that the alternator is charging the battery.

[pajeff02]

High idle is either extra air entering the engine or something out of whack in the throttle body. Have you confirmed that the throttle blade is closed, or just slightly cracked, at idle?