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1999 Chevy Venture High Idle

Nathan Nelson

By Nathan Nelson
in Ask A GM Technician

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Nathan Nelson Enthusiast

Nathan Nelson

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The vehicle has the 3.4L engine. I just did the lower intake gasket, and it ran completely normal. I forgot the 1 nut that secures the heater hose into the thermostat housing, it blew off throwing coolant everywhere. So all I did is take of the tube from the throttle body to the air filter. and the tube running back to the rear valve cover. Installed nut and reassembled. Now the rpm pegs at about 3K-3.5K in park and neutral, about 1.6K in Drive or Reverse. My first thought was vacuum leak, I smoked this way 6 ways to Sunday and cant find any smoke leaking anywhere. I unplugged all vacuum lines to intake while running, rpm goes to about 4k, plugged it with the finger and the rpm goes back to 3.5K telling me the hoses aren't disconnected. I can open the purge valve and idle increases, I can open the egr valve and idle decreases. I own a snapon verus edge. I have live data I can provide while the vehicle is in Park, Drive, and Cold.  any thoughts on what I F*&#ed up?

 

Edit-

     Also no codes or check engine light.

Edited by Nathan Nelson
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Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

I'm betting there's coolant or water shorting some wires on the idle air control or throttle position sensor. I'd hit them with brake clean and compressed air to get all that out of there.

 

If it's still frigged up after that, I'd remove that hose that got knocked off and take a peek inside to be sure something didn't migrate into the throttle plate during the chaos, like a piece of an acorn, or some other mouse food.  

 

Also make sure the throttle plate returns FULLY when you're off the pedal. Coolant could have washed out some lubricant in the cable causing it to hang up.

Nathan Nelson Enthusiast

Nathan Nelson

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22 hours ago, Jsdirt said:

I'm betting there's coolant or water shorting some wires on the idle air control or throttle position sensor. I'd hit them with brake clean and compressed air to get all that out of there.

 

If it's still frigged up after that, I'd remove that hose that got knocked off and take a peek inside to be sure something didn't migrate into the throttle plate during the chaos, like a piece of an acorn, or some other mouse food.  

 

Also make sure the throttle plate returns FULLY when you're off the pedal. Coolant could have washed out some lubricant in the cable causing it to hang up.

 

It acts the same with throttle and cruse cables disconnected at the TB. Used maf cleaner on the maf. I cleaned the throttle plates already and plates close. I did a sweep and TPS appears to be sweeping properly. There is a random drop out that happens just sitting there with the key on. I tried to command the IAC but the scan tool was not updating the position. didnt hear any idle changes. Also I noticed the IAC was getting almost too hot to handle and I would feel the IAC kinda chug chug chug rather then just be a full on and move. Almost like its overloading activing circuit protection then coming back once its down a few degrees. Not sure if thats normal. But I dont think being that hot is normal. I also could not visibly see the iac pintle move. but once I turned off the car the pintle of the IAC shot out of the iac. So I am going to start with that. I will update you if it fixes it. otherwise any other pids to pay attention to and the normal/abnormal ranges, I can get the data. 

Jsdirt Senior Enthusiast

Jsdirt

Posted
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Shouldn't be getting super hot. Could be internally shorted.

Nathan Nelson Enthusiast

Nathan Nelson

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Yeah, I know that much. I am a mechanic, not trying to boast, just more informing I understand the lingo and testing, etc... I am great with R&R, working on diag. I did the head gasket on a 3.1 malibu before I was a mechanic and never had an issue like this. I even kicked over the push rods to have them fly across the garage and it still ran when I got done with it. anyway, new IAC and no change. It actually starts lower and as engine heats up it steps up rpm 2 times before settling at 3.5K

 

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Nathan Nelson Enthusiast

Nathan Nelson

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Posted (edited)

In other news, the knock re tard (I cant believe they block this word... I mean I understand but its not always derogatory)  is all over the place from 3 to 8 degrees.

Edited by Nathan Nelson
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Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

That's strange, along with traction control being commanded at 100% when it's not even moving. Unless I'm reading that parameter wrong, that's an issue. Not sure that would cause a high idle, but that shouldn't be happening.

Nathan Nelson Enthusiast

Nathan Nelson

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Posted (edited)
9 hours ago, Jsdirt said:

That's strange, along with traction control being commanded at 100% when it's not even moving. Unless I'm reading that parameter wrong, that's an issue. Not sure that would cause a high idle, but that shouldn't be happening.

Unless the TCM got a blast of coolant, that took the TCM out. The line that came off sits above the transmission underneath the exhaust. Also it could make since, if traction control is being commanded at 100% it could be the source of the 37% engine load causing the idle to increase. It is only at 1600 rpm in gear, 3600 in part or neutral. If I pull a plug on the intake it starts bouncing off the redline. I Unplugged the maf, iat, tps, egr all at the sometime while running to see if I can get a difference... none.

Edited by Nathan Nelson
added info
Nathan Nelson Enthusiast

Nathan Nelson

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So another tech briefly looked at this with me... and he determined the bracket that holds the throttle cable was bent, causing the cruse control cable to be pulled back slightly. This was one of the first things I did... removed the cruse and throttle cables to make absolutely sure they weren't pulling on the throttle.  Although I did that test... probably with a bad IAC

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Jsdirt Senior Enthusiast

Jsdirt

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That'll do it! Glad you found it. 

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