Idling at 400 rpm

fdjake

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95 Viper...runs good...Idles at 400 rpm...sycn'd throttles (THANKS) Didn't change Idle....Is this a normal idle setting???

Car drops to about 200 rpm when coming to a stop with clutch in.

If this is NOT normal or spec...What should I check???
 

GR8_ASP

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Look at the tach again. You may be misreading it. I know I did when I got my first Viper back in 1995.
 
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fdjake

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I'm not misreading the tach.

When the car is cold it idles at abput 800-900 rpm. Once warmed up it drops to 400. Pulled into a side street yesterday and the car stalled as I pushed in the clutch to down shift. started right back up, got home, sync'd the throttles, seemed to run good but RPM still at 400. If this is what they idle at warm then I'm fine. If it needs to be bumped up a little I'd like to know how, or what to look at.

Thanks again, what a GREAT site this is!!!!!
 

Steve 00RT/10

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The mark that is halfway between 0 and 1000 is actually about 650 RPM if I remember right. It is not 500. To be just below it is normal. That's how GEN IIs are. I assume the same tach in the GEN I

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GR8_ASP

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The tach has 2 tick marks between the 0 mark and the 1000 mark. The first tick mark is for 500 and is slightly larger than the next which is 750. It seems weird as there is no 250 rpm tick. That is why that was my first guess as it is very easy to misread. A correct idle speed is just below the small tick mark, indicating approx 700 rpm.

If you are certain idle speed is as low as 400 then a few tests with the idle air control motor should confirm that it must not be functioning correctly. Idle speed is controlled electronically by opening the idle air flow via the idle air control motor (IAC).

The first step is to see if you have any idle related codes present. Code 24 indicates throttle position sensor problems and code 25 indicates IAC problems. To check cycle the ignition key on - off -on - off - on within 4-5 seconds total. Leave the key in the on position and watch the check engine lamp.Count the pulses to read the code. Note a wider space is used to separate the first and second digits and even longer for multiple codes (note all are 2 digit). 55 indicates end of codes.

If no codes and you still believe the idle speed is low you can check the idle rpm test. That is with the idle air motor pintle fully extended idle speed should be at 704 (note at operating temp). This test requires that you have a DRB to actuate the IAC. A DRB also lets you see the actual engine rpm.

If not I would try the following simple tests. The IAC is on the right side of the right throttle body. A hose connects it to the air cleaner. Check for an obstruction in the hose but that would surprise me as it is a big hose and low flow. With the engine at the higher speed idle disconnect the IAC connector and observe what happens to the idle speed right away and as the engine warms to operating temp. If it stays constant at the high idle speed, or with the idle speed rising slightly as the engine warms, would indicate that the IAC is probably working correctly. At that point I would check the electrical terminals and connectors to esure they are ok. And if all is well but the idle speed still is too low I you will need to get access to a DRB and evaluate the IAC functionality.
 
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