dan239

Recently I had a problem with my truck shifting into overdrive, it would shift in and out several times until my speed increased enough to get it to stop. I recalibrated the APPS and it solved the problem. Some time later I noticed that it was surging at idle in park with the A/C on. I could turn the A/C off and it was smooth, no surge. I recalibrated the APPS again and it quit the idle surge. Everything was smooth and normal.

Today I noticed the idle surge is back. It seems to vary about 50 to 75 RPM. Mostly from normal downward and then back. If I turn the A/C off it will stop surging and idle smooth. If I put it in drive with the A/C on it will be smooth. Nothing is unusual driving the truck. This idle surge is not happening all the time. It is very erratic.

Since the idle is increased with the A/C on it appears to be related to the A/C idle increase. It is changing from the normal idle speed with A/C on down to the idle speed with the A/C off and back, cycling about every two seconds.

Any suggestions appreciated.

Daniel

nitrousn

Sounds like the a/c is low on freon.

dan239

Thanks for the suggestion, I will check it and see if the compressor is kicking in and out. I had not thought of that.

Daniel

dan239

Compressor is not cycling and the A/C cooling seems to be normal.

Daniel

nitrousn

Is the idle still erratic when the ac is working as you say normal?

jrs_dodge_diesel

Now when you say erratic idle do you mean that your tach needle bounces a little bit, or do you actually hear the engine idle funny?

If it is just a bouncy tach needle that is normal. What happens is that the the sensor that senses RPMs is a magetic pickup type sensor. The signal from it goes through the ECM before it goes to your dash guage. Don't know what exactly happens to the signal as on that path but it does get affected slightly. My Ram does the same thing as well as a lot of other trucks here. Unless you are hearing funny noises or it doesn't sound right then I am confident in saying you don't have anything to worry about.

dan239

With the A/C on the idle is varying up to 100 RPM which first got my attention because I could hear it. If I get out of the truck with the A/ C on it is very noticeable that it is surging. It will stop if I put it in drive or reverse and sit still with my foot on the brake. Nothing unusual is noticed when the truck is moving.

With the A/C off the idle is smooth. My comment that the A/C is working normal is that it does not appear to be low of refrigerant which can cause cycling.

I will probably recalibrate the APPS again and see if it fixes the surge again and see how long it lasts this time.

Daniel

nitrousn

If it only does it with the a/c on then your most likely dealing with the compressor clutch cycling. Watch the clutch closely when it is acting up. Do you have any mods done?

dan239

No mods and compressor is not cycling.

Daniel

linetrash75

I doubt this helps you any but my truck does the opposite. In neutral with a/c running smooth as silk, turn the a/c off and it stutters, i wouldn't say it surges. I've caulked this to injectors with 210k on them, a little load adds more fuel and smooths out idle.
I would have say there is something goofy in our a/c did you check freon with a gauge? maybe its low and not cycling compressor might be something telling ecm to change fueling,constantly?

Jed

dan239

I recalibrated the APPS and everything seemed normal for a while of driving. Then I noticed the idle was varying again and a little later I noticed that it was shifting erratic again. So this recalibrate did more harm than good.

Surely someone has encountered this before and found the cure.

Anyone have any more suggestions.

Daniel

dan239

I believe that I have found the problem and fixed it. I will know in a few more days.

I decided to unplug the APPS and plug it back in case I had an intermittent connection. After doing this I recalibrated the APPS and everything appears to be normal once again. If it lasts a few more days I will know that was the problem since it was acting up every day.

If someone wants to try this to solve a problem, it is not hard to do. If you can get your hand up behind the APPS from the bottom the plug must be squeezed on the sides [front and rear on the truck] to release the catch. It will then slide down and out. However, I found an easier way by removing the three vertical bolts that hold the mounting bracket to the engine. They are behind the APPS and very obvious. Then I rotated the APPS and bracket clockwise until I could see the plug. You may need to remove the plastic shield from the APPS to give more room to work. I suggest that you disconnect the batteries first and recalibrate the APPS when finished.

I have not had any idle problem or shifting problem since I did this yesterday.

Daniel