This is topic Idle at 1800rpm or so in forum Tech Talk at Northern California Ford Owners .
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Posted by KCmustangboy (Member # 1927) on
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98 cobra... as I come to a stop the rpms never want to drop back down below 1800 or so. If I just give pop the throttle a little bit real quick, to like 2500, it then drops right down to 800. But if I don't it just says up at 1800 all the time. So I have to do this almost every time I come to a rest at a light. Is this a sticky throttle or possible sensor problem? Also this car has stock plug wires and im sure the plugs are real old to. Changing that all out this saturday.
Posted by 88FOX (Member # 9969) on
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quote:
Originally posted by KCmustangboy:
98 cobra... as I come to a stop the rpms never want to drop back down below 1800 or so. If I just give pop the throttle a little bit real quick, to like 2500, it then drops right down to 800. But if I don't it just says up at 1800 all the time. So I have to do this almost every time I come to a rest at a light. Is this a sticky throttle or possible sensor problem? Also this car has stock plug wires and im sure the plugs are real old to. Changing that all out this saturday.
check vacuum leaks.. egr valve and iac. thats just a start
Posted by 93 twintrbo (Member # 10475) on
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Sounds like a sticking IAC valve. Ford uses Voltage to command the IAC open. It has a specific "park" setting to catch the idle upon decell. Let the car idle high and pop the hood. Tap the IAC valve with a wrench or screwdriver and see if the idle drops to normal. Most of the time the IAC vavles get gunked up and stick. You can remove it and clean the two ports and the pintle with brake clean or carb clean or just replace it.
Lawrence
Posted by KCmustangboy (Member # 1927) on
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After some testing I have decided I believe the throttle is just staying open a tiny bit as you life off and come to a stop or slow down..etc. even in the driveway if you bump the throttle up quick and let it snap back it goes to the correct idle, but if you slow bring down the idle it comes to a rest at 1800. If you then manually give the throttle under the hood a little push closed... it doesn't seem to really move but that little bump moves is back enough to drop the idle down to the normal 800 or whatever. I tried cleaning the throttle body. Could the return spring be worn out? and not strong enough to pull it all the way closed? That is way from in the car you have to either pop the throttle or from under the hood give it the little manual push and it then closes all the way. As I said before the amount it moves is almost impossible to see. But it is clearly there. New spring? thoughts?
Posted by 93 twintrbo (Member # 10475) on
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You may want to check your TPS sensor. If the throttle position sensor has a bad spot, the car will not idle correctly. Put a Digital volt meter on the return signal from the tps. If I remember correctly, it should read close to 1.0v at idle. Slowly move throttle back and forth and see if it sticks at a higher voltage.
Posted by KCmustangboy (Member # 1927) on
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TPS Voltage is fine, 1.00 So It is idles fine. alright around 800 but its like the throttle is sticky sometimes. But like if it sticks all you have to do is light push on the throttle body manually and the idle goes back down to normal. But when driving this is a pain in the ass. Could it be it IAC valve even though I can fix the idle by bumping the throttle? Does the Throttle body just need a good cleaning?
Any ideas would be great
Posted by KCmustangboy (Member # 1927) on
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Update, when the car is sitting in the driveway i had is running and the idle stuck at 1800 or so, I think unplugged the IAC valve. Idle went right now to normal. So just replace the IAC and everything should be fine right?
Posted by dvuspny (Member # 10949) on
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Sounds like you found the issue. Clean-up and re-gasket the idle air control motor before replacing it. Don't forget the temperature sensor is an information feedback for the iac motor also.
Posted by KCmustangboy (Member # 1927) on
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But would it really be the IAC if all i have to do if bump the throttle a little and then it goes back down to normal idle?
Posted by 93 twintrbo (Member # 10475) on
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It could be. It depends on the PCM logic. But most vehicles when the PCM sees an increase in tps voltage will increase IAC position. It will do this to catch the idle and bring it slowly down to normal idle speed.
If the idle valve is sticking at normal "step" you are basically unsticking it by applying throttle. That is why I recommended tapping on the iac valve when it is at the unusual high idle.
Hope this helps.
Posted by KCmustangboy (Member # 1927) on
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tried tapping it... didn't do anything. As I tried to describe before, it's as though if the throttle plate closes slowly... ie normal stopping, it doesn't quite seat all the way shut and rpms stay near 2000. If I just barely touch the throttle to push it shut it does't look like it moves but drops to 800 rpm every time. So maybe throttle body is a little dirty and sticky? That is maybe way when I rev it real quick and it pops shut it does shut all the way and car idles normal... Maybe? I don't know and I am getting tired of it. Thanks for help guys.
Posted by 93 twintrbo (Member # 10475) on
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It is possible the throttlebody is just sticking. Let us know if the problem is gone after it has been cleaned.
Posted by KCmustangboy (Member # 1927) on
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I tried cleaning it best I could with it on there. Should I pull it off and clean in good? Also maybe replace the throttle return spring? or even the spring that is on the actual throttle?
Posted by 93 twintrbo (Member # 10475) on
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I would remove it to inspect it better. its possible you will need to take some scotch brite and clean the butterfly edges and also the buterfly seat area. That way you can get a better look at it.
Posted by KCmustangboy (Member # 1927) on
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Okay so I cleaned the throttle body and it was gummed up pretty bad. I got most everything off but still didn't seem to help. Again it only sticks if the throttle is closed slowly. and even then it will go for a half day without doing it and then start doing it again.
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