Hi, my sister has a 1999 Dodge Ram 1500 with the 5.2L V8. When you start the truck when the engine is cold, it doesn't like to idle at all unless you keep the RPM's up with the accelerator, and then it will idle (at a pretty low RPM) if you let off the accelerator really slowly. Sometimes if it stalls out shortly after starting it, the engine will just turn over, but not catch at all. After waiting a while you can start it up again, but the idle problem still exists. We checked the fuel pressure and its fine. So I'm thinking its got to be some electronic issue. No CEL.

After it warms up after driving for a while it seems fine, but if you let it sit for any period of time the problem will show back up.

What should I start troubleshooting next?

Thanks for any advice.

 

What is the pressure you have seen? What is the psi amount at time of engine off after just being run? What is the pressure with the engine running?

Let's start there.

 

Sounds like the idle air control motor has excessive carbon build up on it. Just had the same problem with my truck. Take the throttle body off, then take the IAC motor off and clean the pintle on the valve and make sure the TB is clean too. That should take care of your problem.

 

I have the exact same issue only its intermittent..guess I will try suggestion above.

 

Having same type of problem with 1996 dodge ram 1500 with 5.2l. Can't seem to figure it out either. tried several different things and still battling the problem.

 

When it's cold out, the ECU is counting on the preset, fixed parameters to keep the truck running. This program mode is called warm up mode or open loop mode.

There's two things that it depends on being correct in order to keep from stalling out and one is correct fuel pressure and, the other is correct air flow. If the fuel pressure is low, the mix is too lean to start a cold engine thus the reason for it stalling out. The pump may be fine and, the pressure may be fine once it's warmed up and running but, not adequate for cold starts.

The reason it why it won't start immediately after a stall out is because unburnt fuel remains sitting in the combustion chamber after the stall out. It can't start because it's partially flooded out and can't ignite that wet mixture.

After it evaporates a bit, then it starts back up. The same symptoms can be found with a leaky fuel injector as well. Same exact symptom after a stall out.

In this case, either you have a lean mix due to two things:

1. Low fuel pressure

2. Lack of air flow due to clogged IAC passages at the TB or, bad IAC motor

Both of those will cause the same exact issues. At the time when the truck is started, the IAC motor is supposed to open up a preset, fixed amount to allow proper air flow at startup. This is with the plates closed. During warm up mode, the ECU is not in control over the IAC. As stated, it's using preset, fixed parameter based values to set the gap at the IAC motor. In this mode, the ECU doesn't monitor the A/F mix as it's assuming that all systems are operating normally. It has no idea that it's not getting enough air or enough fuel. In this case, holding the throttle plates open is the only way to keep it running as it's the only way it's getting any air.

Once it reaches 180º, the ECU switches over to closed loop mode and begins to adjust the IAC gap, the timing, the injector pulse width, the coil pulses and uses all the sensors to make fine adjustments to achieve the proper A/F ratio. This is why when it's warm, it runs great.

Now, if you shut it down for ten minutes or so, it should still start back up just fine as it's still hot and will be running in that controlled mode. However, if it were to cool down below 180º, then you would see the same issue resurface. That's when you know it's an IAC related issue.

However, if after only a few minutes the problem resurfaces, it's leaning more towards low fuel pressure. Low fuel pressure creates hard starts in general and, the colder it gets, the worse it gets because it causes gas to contract thus reducing the pressure to the point where the vehicle won't start.

This is why in the summer you won't notice this as much. The heat causes the gas to expand thus increasing the pressure to within normal starting pressure.

But, do check both areas. I would first run this simple test before tearing anything apart and / or making any adjustments.

Turn the key to <ON> once and measure the psi at the rail. Do not start the truck at this time. Just turn it to <ON>. Turn the key to <OFF> and then to <ON> and measure the pressure at the rails. Repeat this one more time.

Note pressures on all attempts. ON your first go around, the reading should be up to or near full psi rating which is around 50 psi. If on attempt No 2 it is around 50, your still good to go. IF on attempt No 3 it is around 40 psi, you have a problem with your pump or, there's a leaky injector. If on any run, you note a fair amount of pressure drop, you have a problem. It should hold almost full pressure for quite a long time so, any drops and your looking at a bad pump or a leaky injector or even a possible fuel leak. I just want to inform you of all the possible causes here even though you may not have a fuel leak or leaky injector.

Now, for the IAC. There's no way of knowing what the motor steps are without using a good scan tool so, checking that is out. But, what you can do is simply disconnect the battery and then pull the air hat, remove the sensor harnesses, remove the throttle cables, remove the four top bolts and take the TB off. Flip it over and note the bottom, rear area. If it's all black and sooty, it's most likely clogged up. To clean that, simply take all the sensors off first followed by removing any gasket material that may have stuck to the bottom. Then, using Acetone or TB cleaner, and a variety of other solvent such as Lacquer thinner, turpentine, mineral spirits, denatured alcohol etc, and scrub the crap out of it until all that black stuff is gone.

Be very careful when you clean the IAC assembly for that pintel assembly can be damaged very easily. Do not bend, push or apply any side load or direct pressure on it at all. Clean all the black stuff off as well as you can.

Using a new gasket, reassemble it and place it back on the intake. Torque it down to 19 - 20 ft lbs max. Attach all the vac lines, sensor harnesses and throttle cables. Place the air hat back on and your good to test it now.

If it was the IAC, it should now start and run fine.

 

Sorry for piggy backing on your thread
1997 ram 1500 4x4 5.2 throtle body

I'm having same problem at start up only i resently changed the IAC and the TP account was not idling right would riveup on its own the TP fixed the problem, the new IAC was not the same lenghth but the service guy said it was the updated version. put it in all good ran fin until last week started with this problem went on a long road trip and would have to idle the motor to keep it running every morning.
I'm going to clean and if i find the old IAC part put it back in will let you know what happens.

 

I also have a '96 with the 5.2L and am having the same problem. So, what turned out to be the cause of and the fix for the problem? Thanks.

 

3 year old thread guys... don't expect anyone to answer.... Start new threads please. Each of you.

 

I have this 1500 96 ram and just a problem that it wouldn't they running it would start but wouldn't idle on it's own. So I cleaned the battery posts just incase cause they were dirty and I put in one container of that gasoline stuff for gas tanks and I must of got water from not fulling it and leaving it half to a quarter tank and with these canadians winters with the warm cold they seem too form condensation.