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High idle after changing coolant


stenk
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Hello there,

 

I changed coolant on my 88 Pathfinder VG30i this weekend. I flushed it 3 times with a distilled water before I filled it with new coolant. After that my truck idles high, rpms stay between 1.5k-2k. And they won't come down anymore. Sometimes when I very gently push the gas pedal and then let it go, the revs come down to normal level (approx. 800rpm)for a sec and then go back again. Like something is stopping it to idle normal and pushes the revs high. I took it for a drive and nothing changed. Everything else works, drives great and blows normal heat to the cabin. No ECU codes at the moment, everything is ok.

 

What happened? Has anyone experienced something like this? Maybe the engine was too hot before I added new water into it and the sudden temperature change made something crazy.

 

Hope you can help me.

 

Sten

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Have you completely burped the system of air? There's a fast idle plunger run off a wax element that pushes on the throttle cam, it needs to have coolant circulating properly through the throttle body for it to work.

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Well, I hope so but I am not 100% sure. When I added coolant, the white plastic screw was removed from the upper radiator hose and air bubbles came out there. I filled the radiator to the max and at the same time coolant started to come out from the screw hole. Then I put the radiator cap and the screw back. Then I let it idle for some time (the engine seemed warm enough). Later when the engine had cooled down, I filled the reservoir tank back to max, the radiator was already full.

Did I miss something? Maybe there is some air in the system left but how can I get it all out then?

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Did you have the heater on full hot and the fan on? When it's fully bled there will be no buddies from the radiator or bleed calve and the heater will about burn you at idle. Sometimes these motors can be a pain in the butt to bleed, jacking the front of the try know up a little helps.

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I'll try to check it once more and see what happens. Also I will take the air cleaner off and check the thermo unit, maybe it doesn't move anymore. If it won't move, then I believe that there is the problem why the idle is so high and wont come down.

But when should I turn the heater on? While adding coolant into the radiator and the bleeding screw open? What fan speed should I use? The car engine has to be working?

I am away from home at the moment so I can start working with the car on Saturday. Let's hope that it's an easy fix! :happy:

Edited by stenk
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Did an 88 still have a carb on it? I guess because it's not a US model it could huh...I don't have any experience with this but I like what Kingman had to say about that high idle circuit..that's good stuff.

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Did you have the heater on full hot and the fan on? When it's fully bled there will be no bubbles from the radiator or bleed valve and the heater will about burn you at idle. Sometimes these motors can be a pain in the butt to bleed, jacking the front of the truck up a little helps.

Holy crap. Edited this for grammar.

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Well, it was only a simple fix this time. There really was some air left in the cooling system. I took off the air cleaner and started the truck. The thermo unit even didn't get hot and nothing moved. (it meant that no coolant is flowing into it). Stopped the truck and opened the clamp on the hose next to the unit a little bit and started to move the hose. Then air bubbles and some coolant started to leak. Soon only coolant leaked and the thermo unit got instantly hot!

Tightened the clamp back and started the truck. The idle instantly fell down back! :happy:

Only thing I noticed is that the thermo thing doesn't move as much as it supposed to. Maybe one day should get a new one. But at the moment I adjusted the screw a little and now everything works brilliantly!

Thanks Kingman for your advice, you were right!

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