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Author Topic: Up & down idle 88 Duke when warm  (Read 33069 times)

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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #15 on: December 21, 2018, 07:05:48 am »
Was the EGR valve actually bad?

Was there vacuum on the EGR vacuum line?  It would seem that, when you unplugged it, there should have been a change, unless the line has a leak somewhere.
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TopNotch

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Re: Up & down idle 88 Duke when warm
« Reply #16 on: December 21, 2018, 07:49:09 am »
Quote from: GTRS Fiero on December 20, 2018, 09:43:21 pm
I'm feeling dense, tonight.  Does the back pressure make the EGR open or close?

Open. You don't want the EGR open at either wide-open-throttle or idle. At idle, there is a lot of vacuum, but no back pressure. At wide-open-throttle, there is plenty of back pressure, but very low vacuum. At cruising speed, you get both, and the EGR opens. It's a very simple system on the duke, with no electronics or solenoid involved.
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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #17 on: December 21, 2018, 07:56:54 am »
Hmm.  I wonder if the EGR is special, to accommodate this.  Just because it bolts up doesn't mean it is the right one.
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Fierofool

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Re: Up & down idle 88 Duke when warm
« Reply #18 on: December 21, 2018, 08:28:11 am »
It is special.  Those are the ones that require the base gaskets with two holes.  I think you were the one that encountered that style gasket. 
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TopNotch

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Re: Up & down idle 88 Duke when warm
« Reply #19 on: December 21, 2018, 11:08:49 am »
Quote from: Fierofool on December 20, 2018, 03:12:09 pm
You can test the EGR valve by placing your fingers underneath and feeling the diaphragm.  Push up on it and cap the nipple with a finger.  If the diaphragm moves down, the valve is bad. 

Unfortunately, this test does not work on a duke EGR. About the only test you can do is push up the diaphragm while the engine is idling. If there is no change, you know the EGR is leaking or stuck open.
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Donster

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Re: Up & down idle 88 Duke when warm
« Reply #20 on: December 21, 2018, 11:18:42 am »
Quote from: Donster on December 21, 2018, 05:56:37 am
Again, does anyone have experience with blocking out the EGR on an 88 L4? I can have a cover-plate and gasket made within minutes and permanently plug the hoses.
Thanks

\D

Anyone?
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TopNotch

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Re: Up & down idle 88 Duke when warm
« Reply #21 on: December 21, 2018, 01:06:04 pm »
I think you should try it, and then let us know the result.
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Donster

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Re: Up & down idle 88 Duke when warm
« Reply #22 on: December 22, 2018, 08:16:40 am »
Tried it, only a nominal improvement, barely noticeable.
Will replace plugs next.

\D
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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #23 on: December 22, 2018, 08:20:04 am »
I'm no expert on the Duke, but I suspect a sensor issue.  The IAC or CTS, maybe.
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Donster

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Re: Up & down idle 88 Duke when warm
« Reply #24 on: December 22, 2018, 10:51:10 am »
Quote from: GTRS Fiero on December 22, 2018, 08:20:04 am
I'm no expert on the Duke, but I suspect a sensor issue.  The IAC or CTS, maybe.

They would both throw an error code.

\D
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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #25 on: December 22, 2018, 11:20:12 am »
Maybe.  If you think about it, the plugs, plug wires, etc are in use while the engine is cold.  Everything is managed by the ECU, using preset values.  After the engine warms up, the ECU relies on inputs from the sensors.  The CTS tells the ECU when the engine it is warm.  In theory, the idle is then controlled by ECU using input provided by the IAC.  Something is either providing incorrect input, or the ECU is interpreting the input incorrectly.
« Last Edit: December 22, 2018, 08:18:50 pm by GTRS Fiero »
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Fierofool

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Re: Up & down idle 88 Duke when warm
« Reply #26 on: December 22, 2018, 06:34:27 pm »
I can't speak to the IAC trouble code since I've never had problems with one, but I can tell you that the CTS can be faulty and not set a code.  Even when it's severely at fault.  My CTS was sending info that the coolant was below freezing, but never set a code. 
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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #27 on: December 22, 2018, 08:23:47 pm »
My IAC was bad, and did not set a code.  Of course, this is on a V6.  Another guy here locally had issues, but no code.  We replaced his IAC, and the problem went away.

For the CTS, there are only certain conditions under which it will set a code.  Neither of them are because the sensor is bad.

It may or may not matter, but these were all V6 applications.
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GTRS Fiero

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Re: Up & down idle 88 Duke when warm
« Reply #28 on: December 22, 2018, 08:32:02 pm »
On PFF, for your consideration, a similar issue:
http://www.fiero.nl/forum/Forum2/HTML/142073.html
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Donster

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Re: Up & down idle 88 Duke when warm
« Reply #29 on: December 28, 2018, 08:39:55 am »
OK, as GTRS assumed correctly, the plugs were not the issue, but after 4 years, a change was not a bad idea anyways. :-) Thanks for the link!
Does run a bit better but idle issue persists.
Also adjusted the TV cable, so it shifts much better now also.
Tomorrow I'll replace the IAC and report back.
\D
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