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High idle, fuel pump? by 84pierro
Started on: 07-15-2014 02:56 PM
Replies: 5 (169 views)
Last post by: phonedawgz on 07-15-2014 05:57 PM
84pierro
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Report this Post07-15-2014 02:56 PM Click Here to See the Profile for 84pierroClick Here to Email 84pierroSend a Private Message to 84pierroEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hey all, First ever post but have referenced multiple threads (thanks you all!) many a time since purchasing Pierro about a two months ago; my 84' base model Fiero, with 50k original miles, clean and pretty as a whistle.

Just as expected, a couple of the typical Fiero problems have come my way; headlights dont flippy(we'll get there), shifter cables replaced after heat got the best of 'em, and the basic tune up and maintenance as to expect with any 30 year old car.

But just recently I ran into (yet another) classic 30 year old fiero problem.
As of about a week ago the idle has been pretty sporadic; between 2500 and 3k (:/) then when is expected to drop as engine warms, jumps up and around 3, in gear avg 2500.
After exploring the interwebs and learning all about the ECM, IAC's, MAP's, and DVD's; I tinkered some more:
Checked all fuel lines and vacuum hoses and cant seem to find any cracks or leaks.
Did notice a couple random untightened screws in the throttle body and a diaphragm directly behind it was barely hanging on (not sure what it is)
Cleaned the IAC, checked all wires and connections and put it all back together.
I started the car w/ the air cleaner off to plug the hole and see if faulty IAC (http://www.fiero.nl/forum/A...219-2-075478.html#p6)
She idled at a pretty 1200rpm
I then noticed the fuel pump continuously spraying fuel into the carb (?)
Put the air filter back on and car idled at a pretty 1200 and warmed up and jumped up to about 2k
Now, she starts up and holds a decent 12-15 but as soon as i start driving, she cranks back up to a solid 25k, idles or neutral. and drops when in gear.

As this is the first engine I've gotten fully hands on with (im 21) i'm a little lost as to what's actually going on, should the fuel pump continuously dump fuel into the carb (my brain thinks not) and does that mean I have a vacuum issue since it jumped back up with the air cleaner re-installed? Really enjoyed the low idle but i've read that 2k is to be expected?
Would love some feedback!
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phonedawgz
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Report this Post07-15-2014 03:15 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Is fuel being injected into the throttle body bore when the engine is running or when the engine is off?

Yes fuel should be injected continuously when the engine is running. Stop the flow of fuel and the engine dies.

If it flowing in with the engine off then there is a problem however that wouldn't cause a high idle.

Does your check engine light work, that is does it come on key on engine off? It should

Assuming it works does the check engine light come on otherwise?

Considering that the idle seems to be ok at times and not ok at times tends to make me think the ECM is commanding it. One thing to try to see if the ECM can control the idle
The question to start with is the ECM commanding the high idle, or is the high idle coming from a vacuum leak?

If your check engine light works but doesn't come on during the high idle (let it idle for at least 60 seconds) then it would sound like the ECM is commanding it.

Considering that the idle seems to be ok at times and not ok at times tends to make me think the ECM is commanding it. One thing to try to see if the ECM can control the idle would be to warm it up, turn it off and then start it back up. See if without moving the ECM has it idling the correct RPM. If it does turn off the engine remove the IAC and screw the pintle almost all the way in. Replace it and start it. The engine should be running fast when you start it (2500 RPM). Don't touch the gas and see if the ECM reduces the idle to what it was before. If so that would indicate the ECM is controlling the idle (IAC).

[This message has been edited by phonedawgz (edited 07-15-2014).]

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84pierro
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Report this Post07-15-2014 03:34 PM Click Here to See the Profile for 84pierroClick Here to Email 84pierroSend a Private Message to 84pierroEdit/Delete MessageReply w/QuoteDirect Link to This Post
Check engine light works, does come on with the engine in. Is not on when the car is running.
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Report this Post07-15-2014 04:32 PM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
Welcome to the forum

Sure sounds like a vacuum leak to me...or could this also be the throttle position sensor?
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84pierro
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Report this Post07-15-2014 04:41 PM Click Here to See the Profile for 84pierroClick Here to Email 84pierroSend a Private Message to 84pierroEdit/Delete MessageReply w/QuoteDirect Link to This Post
how do i go about fiiiinding it?!
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phonedawgz
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Report this Post07-15-2014 05:57 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
I don't think it's a vacuum leak. If the ECM sees too high of an idle for long enough (like 60 seconds) and can't control it, the ecm is programmed to turn on the check engine light.

Try this and see what happens. Get the trouble to occur and turn off your engine. Take out the IAC. Stick your finger in the IAC hole and fine the hole that leads off to the intake manifold. Have your assistant start the engine. Use your finger to control the idle speed. If when you cover the hole to the intake manifold (the hole that is sucking) the engine stays running fast the problem is a vacuum leak. If when you cover the hole the engine slows down to 800 or below (including stalling) then the problem is that the IAC is staying open and most likely the ECM is doing it. It could also be that the IAC is sticking because of crud in the IAC hole that your finger is in.
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