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  #1  
Old November 4th, 2005, 12:15 AM
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Doug Walker
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Rover Game....

Connect the dots:

1. Chammy (my 110) has three idle speeds; 400rpm, 800 (chip designated normal) and 1100. The selction is random with no pattern, and whatever speed she starts with stays that way for the duration of a run. ie: Every time I turn on the key and start up, the idle will be one of the three and will stay in that 'setting' until the ignition is switched off.
2. Sometimes, their is also a low-volume high-pitched rpm-related whine that comes out of the passenger front speaker no matter if the radio is on or off. Stays that way until ignition switched off.
3. When the idle rpm is in the 400 'mode', there is sometimes (but not always) a steady whistle (not rpm related) coming from behind the plenum (can't track it precisely -- like a ghost it moves away when you get close). Doesn't seem to connect to speaker noise in #2.

None of the above effects performance in any way. Power curve is strong all the way to 5000 rpm. It's just an annoying weirdity....

For you guys who like solving puzzles!

Doug W.
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  #2  
Old November 4th, 2005, 01:12 AM
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IAC stepper?
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Old November 4th, 2005, 09:11 AM
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Chris Davis
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Your idle is determined by the ECU and adjusted via the stepper motor--the stepper motor is used only at idle and one way to "cut" it out is to press on the accelerator or have the ecm think you did via the throttle position sensor. Those are the two items that I would check out first. O2 sensors would be next. What sort of induction system do you have? My DII has a different IAC set up. If the stepper/tps check out fine, then either your ECU is misinterpretting the data, or your sensors are sending wrong data--I would start with swapping the ECU with a buddies and just rule that out.

I don't think it would be related to fuel delivery since it is so consistent one the truck is started, although I have learned not to rule anything out with a rover, so if you can't find anything from above, I would probably check that next starting with the filter and pressure check.
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  #4  
Old November 4th, 2005, 11:01 AM
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Robert Dassler
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I'd also check the stepper motor housing...it bolts to the back of the plenum and is sealed with a gasket...they have been known to get loose and cause an intermittent vacuum leak...ditto the intake gasket...run a torque wrench over the 12 bolts to be sure. Also check the vacuum line that runs to the fuel pressure regulator.
Rob
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Old November 4th, 2005, 02:47 PM
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Doug Walker
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Rob -- I think u are right about an intermittent vac leak. I have replaced stepper and 02's with no change. I have also flipped ECUs (I have a couple) and no change. It won't be for a couple of weeks until I can do the vac inspection -- thanks for the tip on the plenum bolts -- hadn't considered that!

I also wonder if a bad fuel temp sensor, coolant temp sensor could cause these symtoms. Thoughts?

DW
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Old November 4th, 2005, 02:59 PM
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I from my experiance bad temp sensors cause it to stall at some point while the engine is warming up. And I think the ECu would catch if the temp sensor is bad.
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Old November 4th, 2005, 03:01 PM
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well...anything's possible, but I'd probably assign them a low probability. The water temp sensor is a significant input into the ecu when it comes to determining the fuel map...it is weighted about 60%...but the IACV system is not terribly temperature sensative and should be able to control the idle speed no matter what the temp. I would be looking for an outside influence, such as a vacuum leak, that is rendering the system ineffective. Also, It takes it's RPM pickup off of the ignition coil. Are you running any kind of non factory ignition components that may be giving it a weak or varying signal? Is your distributor shaft tight, or does it wobble a bit?
Rob
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