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Discussion Starter #1
Hello,
I´ve a little problem with my ´95 eldo...

If the engine is on and the car are not rolling, the engine run with 800 UPM very nice...

If I drive and press strange the accelerator pedal the engine run very nice...

If I drive with low power (straight road or downhill or before I stop) the engine oscilate from 2000 UPM to 1900 UPM (for example). I can feel these oscilation.
These problem is from 0 to 3000 RPM and not at every time. I think it´s 20 % from the drive from 0 to 3000 RPM at the last 80 % the engine run very nice.
An I´ve I drive withou pressing the accelerator pedal (downhill etc.) the problem is the same.

If I drive in higher RPM (over 3500) the engine run very nice.

Now, I´ve cleaning the EGR valve and the problem is the same.

No error codes.

Engine and car has 30.000 mls.

What is it ???????
Thank you very much.
With best wishes from germany.

Frank
 

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2005 CTS-V, 1994 Infiniti Q45
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7,658 Posts
Frank

Let me clarify...

The engine runs fine most of the time but if you use less than 20% throttle or so the engine doesnt like to stay at one RPM (it hunts)

When was the last time you did a tuneup or any sort of maintenace???
 

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This is a Northstar car, right...???

It sounds like the idle speed control may be having problems when you are coasting with your foot off the throttle. This could be due to several potential problems.

The first thing that I would do is to take the inlet air duct off and hold the throttle blade wide open (engine off) and spray the backside of the throttle blade and the perimeter of the throttle bore with carb cleaner and scrub it with an old tooth brush to clean off any deposits. The deposits may be thick enough to be partially blocking off the air flow around the perimeter of the blade when it is nearly closed while coasting causing the RPM to dip low then the idle speed control extends the throttle to prevent a stall. Clean the throttle body thoroughly, disconnect the battery negative terminal for 60 seconds to reset the idle learn offsets and drive it and see if it is OK.

The other thing to do is to check the operation of the closed throttle switch. With the engine running and in gear, enter into the onboard diagnostics by simultaneously pressing and holding the OFF and WARMER buttons until the onboard diagnostics activates. After any codes display the system should prompt you with PCM? Answer yes with the HI button. Now that you are in the PCM mode the icons on the climate control panel take on new meanings. The LO icon represents the status of the closed throttle switch inside the idle speed control motor. If your foot is on the accelerator pedal pressing it even slightly the LO lite should be out indicating the switch is open due to you opening the throttle. If you have your foot off the accelerator pedal idling or coasting then the LO icon should be on indicating that the throttle lever is resting on the idle speed control motor plunger. Do your coast maneuver where the RPM wants to hunt and watch the LO icon while coasting. If the LO icon is blinking on and off it indicates the closed throttle switch is opening and closing which may be what is causing the problem. Something is causing the switch to open and close intermittantly which is throwing off the idle speed control signals to the idle speed control motor. Either something is restricting the throttle travel or dragging on the throttle cable or pedal when you lift off of it or the closed throttle swithc inside the idle speed control motor is wearing out and sticking and going intermittant when it is closed. Stop and idle for awhile and watch the LO icon to see if it ever goes out when just sitting and idling...if it does then I would definitely suspect the closed throttle switch inside the throttle body. Replacing the idle speed control motor is most likely the cure.
 

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I believe I have the same exact problem and I was just going to start a thread till I came across this one. I have a 1993 Seville STS with the Northstar. The car idles excellent all the time nice and smooth right about 800 RPM. The problem occurs just about all the time. On light steady acceleration the RPMS wont jump much (maybe 100 RPM's) but you can feel the car oscilatate. But the problem is most evident when you let off the throttle completely to coast. When you let off at about 60 mph approx 2000 RPM the rpms wont fall till 1600 then it will surge back up to like 1800 then fall to 1400 then surge again to 1700 then fall to 1000 and surge to 1300 then it just about flattens out and stays about 1000 rpms. This happens on a level coast no incline hardly at all. It had the problem since I had the car. So far I have cleaned the throttle body and put in a new air filter and replaced the PCV valve. I have no codes.
 
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