I have done a little searching on this forum, but i can not find anything that explains what is going on.

I bought my truck at the end of the summer(when it was warm) and never noticed any problem when it was idling. It is getting REALLY cold in Michigan now, and when i start up my truck before school and let it idle it starts to sound like its flooding/stalling or something. The engine runs fine for about 30 seconds to 1 minute, then the rpm's get shaky and low and the truck starts to shake and make a weird sound. Keep in mind this is ONLY from a cold start, and it does not do it while driving(if i get in and start to drive immediatly) As soon as the engine temperature rises to the "normal" marks on the meter, i can let it idle all day long. In order to stop it from stalling i have to rev it up constantly for a few minutes untill the engine temperature has risen.

I'm wondering if anyone can shed some light on my problem, it is not really affecting me now, but when the snow hits it will be a major problem if i cant let my truck idle to help get the ice and snow off.

Thank you very much

 

mine did the exact same thing for a couple days a while back when it started getting cold but it seemed to clear itself up when I ran a can of seafoam through a tank of gas so I'm not sure if it was temp related but I remember thinking that at the time.
Could be your IAC (idle air controller)

 

Bad winter fuel mix.
Gummed injectors.
Too thick motor oil.

Was it doing this 'cold start' issue even during the summer? or only when the temp dips down below freezing?
Any codes?

 

In the summer it never did this, only when it started to get down into the 40's and 30's during the night and morning. The check engine light hasn't come on, if that is what you mean by codes.

 

Every so often mine plays a similar prank.

When it gets shaky and rough, I can hear a sucking noise from the intake that gets progressively louder, then it fades away, the rough shakiness disappears, and the motor runs fine. Like I said though, it only does it here and there, not every time I start it.

 

mine kinda does this too. it has a little bit of a rough idle. its nothing horrible. it will idle without dying but every so offen if you sitting in the truck u can feel it shake a little bit but when u take off it runs like a top. im not sure whats causing the rough idle. i changed plugs, wires, cap and rotor and still does it

 

The main two components affected by thermal change at cold startup is the ECT and the IAT sensor and, that little sensor (ECT) is the MASTER sensor and everything else is based off it's output. The colder your coolant, the more fuel is applied.

During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop mode. Open loop mode lasts for a duration of 2-3 minutes or, up until your engine temp reaches ~180º. After that, the timer puts the PCM into Closed Loop Mode providing the ECT has reached it's minimum value - around 180º.

When you hit the key, the fuel system is activated. Then, the PCM pre-positions the IAC stepper motor. It then determines atmospheric air pressure from the MAP sensor input to determine the fuel amount. The PCM then monitors the ECT sensor input. It now MODIFIES the fuel amount based on it's output voltage. The IAT sensor is monitored and the TPS is monitored.

The ASD relay is energized for 3 seconds and the fuel pump is energized through the fuel pump relay through the PCM and lastly, the O2 sensor heater element is energized via the ASD relay. However, as was stated before, the O2 sensor input is NOT used by the PCM to calibrate the A/F during this mode.

Now we go into Engine Startup Mode / Open Loop Mode. When the starter motor is engaged, the PCM receives input from the the following:

- Bat voltage
- ECT sensor voltage
- CKPS sensor
- IAT sensor
- MAP sensor
- TPS sensor
- Starter motor relay
- CPS

The PCM monitors the CPS for a brief period of time for output. After that, the pump is activated by the PCM through it's relay.

Voltage is then applied to the FIs via the PCM through the ASD relay. The PCM then controls the injector pulse width by turning the ground circuit to each injector on / off.

Last, the PCM determines the proper ignition timing based on the input it receives from the CKPS. Here's another factor that may be the root cause for your issue. It may be that your TIMING is off at this stage and, only until it goes into closed loop mode can it be corrected. If those last changes do not remedy the issue, that's most likely the cause and I will explain later why in the section called: Closed Loop Mode

Now we go into warm up mode which is Open Loop Mode.

During Engine Warm Up / Open Loop Mode, the following three inputs are used:

-Battery voltage
- CKPS
- ECT
- IAT

The next phase is Closed Loop Mode where, the PCM now adjusts the ignition timing by first using the O2S input and adjusts the A/F ratio. It also adjusts the engine idle speed through the IAC. Last thing to happen is the PCM turns the ground path on / off to the coil so it can correct the out of balance condition.

This is where I believe your trouble is rooted. It's in the open loop mode and, most likely a timing issue. That will also explain why when it gets colder out the worse it gets- it runs it richer making the timing worse or happen more frequently.

So, what you need to do is have someone with a good, DRB scan tool to monitor it while in open loop mode to see what is going on with your timing and A/F ratio at this stage. Again, cold temps affects your ECT input voltage and your IAT sensor voltage, both of which will cause the engine to run rich. Colder it gets, worse it gets as it applies more fuel to keep it going during those super low temp mornings. I used to live in Boston and know what that's all about...brrrrr.

 

ok well i work at a shop and we have all snap on scan tools so i think we can figure it out. so what specificly do i need to look at

 

If your scanner is able to monitor open and closed loop modes, this is what you want to look at. How long is it running in open loop mode and at what condition/s does it switch over to closed loop mode and, does it switch back and forth from open to closed while idling.

Your going to be looking at the ECT and your engine temp, your IAT and incoming air temp, MAP and it's relationship to vacuum at the intake, your battery voltage / charging system and, your A/F ratio / mix at cold startup. One other thing too, you will want to monitor your fuel pressure during all of this.

What kind of scan tool do you have; hand held or software on a computer?

Before you dive into the fine details, have you verified that there are no vac leaks at the intake level at cold startup and that your fuel pressure is dead on the money?

See, the PCM is "assuming" that the following items are operating within normal range in open loop mode: Fuel pressure, IAC, and I believe the CPS too.

- fuel pressure: if fuel pressure is out of whack, the PCM has no way of knowing. You may be running lean, which would cause the engine to run really rough- especially on a cold startup. The colder the temp, the more fuel is required to keep it running without having to step on the gas.

Since the PCM is not controlling the A/F ratio / mix at this stage, there's no way for it to correct it until it goes into closed loop mode. It will run horrible while in open loop mode when the pressure is low.

The opposite of this would be a pump that is putting way too much fuel in vs intake air flow as this would cause it to stumble and smother the air thus causing it to stall out. In this case, if one were to step on the gas, it will most likely want to stall out vs revving up.

Now, the IAC can also produce the same end result as is described above because, it is running on preset values that the PCM is programmed for. If the IAC motor step value is different vs. what it is set at the PCM, it may choke the air supply thus causing it to stall and stumble and, when you press on the throttle, the plates open up thus allowing more air into the chamber to allow it to burn thus keeping it running. Once it goes into closed loop mode, the PCM takes over and adjusts the IAC based on the readings / feedback it receives from the O2 sensors, IAT, ECT, CKPS, CPS and MAP. Once it takes over, the truck runs fine from that point on.

This is why we need to look at open mode. Your issues are rooted in that mode and not in closed loop mode.

I have a bet on it being either fuel or air related. IAC or Fuel pressure. Those are the two most likely factors to be out of whack. The other two to check is your CPS voltage / values.

If the CPS data is out, the timing will be off. You will have more of a timing issue vs. it being an A/F issue. In this case, you would be looking for misfires or, knock sensor errors or a large offset between the crank and cam. Now, I don't think your tool will be able to read those. There's only a few that I know of that can read that data and those are MRBII/III, DART and custom software tools that are specifically tailored to Dodge OBD II PCMs.

 

mine is doing the same but i got a code not sure what code but any help (the codes that comes up is p 1281 and p 0455)