I can't seem to get the 'search' function to work anymore, so I apologize if this has been covered before...

After sitting for a long period of time (seems to be worse in cold weather), the engine stumbles and idles roughly when first started. Sometimes it's worse than others. I suspected the IAC valve immediately but there was little if any improvement when I replaced it with a new one (from Autozone). The new one looked slightly different but bolted up and plugged in ok. Is there any way to independently test the new IAC to be sure it's operating to spec (without buying another new one)? Is there anything else that could cause this? The truck has 53k miles on it and I haven't changed plugs/wires yet, but it runs like a top after warming up for 10 minutes or so... Any ideas?? Thanks in advance.

EDIT:

For some reason, my signature won't show up...
My truck:

2000 Ranger SC
4x4 Off-Road
3.0l
auto

 

Welcome to FTE!

I doubt it's the IAC, since the symptoms remain the same witht he new one.

A stumbling idle on cold start can also be caused by leakage of fluids into the cylinders. For example, an injector leaking down could flood a cylinder which would cause the engine to run rough until the excess fuel is burned. Leaky head or intake gaskets would allow oil or coolant to get into the cylinders.

 

Thanks for the response.

It doesn't do it all of the time. Mostly when the weather is cold. Also, I haven't noticed any coolant or other fluid loss. Is there a temp sensor somewhere that could be malfunctioning and confusing the PCM when it's cold outside? What about the plugs/wires? It's probably about time to do those anyhow.

Any chance I got the wrong IAC? It does look slightly different than the original one but the bolt-holes lined up and the electrical connection fit so I used it. It seemed a little better after I first changed it but that could be my imagination or a slight change in the weather we've been having (it's a little warmer than it was last week). Any other thoughts??

 

The new IAC is behaving like the old one, so I would not suspect that the new one is wrong for your application.

There is an Engine Coolant Temerature (ECT) sensor which is responsible for letting the computer know the engine temp. Follow the upper radiator hose to where it attaches to the upper intake, that's where you will find the ECT.

 

The new IAC isn't behaving exactly the same, or so it would seem. That and the different appearance are the reasons that I was questioning it, but you're probably right.

Thanks! I'll take a look at that as well.

On a separate topic (I know this isn't the area to ask this), what do I need to do to have my electronic signature show up? I'm checking the 'show your signature' box before I submit my posts...

 

The signature will show up at the bottom of posts for members of Club FTE. For all FTE members, the signatures are still viewable by anyone who runs their mouse over the word "Signature" located in the upper right-hand corner of the post box, along with the other member info.

 

I changed my 02 sensor and it improved cold idle significantly.

 

Ok, thanks.

I'm hoping that's not the problem. Did yours throw any codes when you were having problems with your O2 sensor? Mine hasn't thrown any codes yet...

 

nope it did not

 

The HO2S sensors do not determine the A/F ratio until they reach the 600F operating temperature. If it's rough until it warms up, then it's not the HO2S sensors.

It could be a dirfty MAF, or stuck EGR valve as well. Both will give A/F ratio problems. It could also be fouled plugs that have to burn off oily deposits before they function properly. This could be caused by bad valve guides. Bad plug wires will also do this. If there is a small break in a wire, it will arc when cold, but as it heats up from the arcing, the wire's length will expand, and the short will "fix" itself. Iv'e seen this happen to a homeowners' powr line to his house before.

 

On Ford OBD-II systems, the O2 sensors are heated, and hence the system goes into closed loop (that is, O2 sensor feedback is utilized for A/F calculations) usually only about 60-90 seconds after a cold start, regardless of engine (coolant) temperature.

Cleaning the MAF and EGR valve could ineed be something worth considering.

 

He didn't state how long it ran rough - I was offering that one of the sensors for the closed loop system (IAT, MAF, IAC) was malfunctioning. I have had a similar problem before on my Taurus.

 

We're on the same page. I figured it was worth pointing out the difference between the "older" engine management systems (where the engine had to actually warm up enough so that the exhaust would heat the sensor to the required temperature), and the "newer" EEC-V (OBD-II) system (where they heat up much sooner, as described in my previous post). I should also add, though, that use of heated 02 sensors actually started even earlier than OBD-II changeover ...you can find a lot of pre-'95 Fords with heated 02 sensors.

FWIW, it appears that you don't feel that an 02 sensor is the cause of y2kranger's bad idle condition, and I also feel the same way.

 

that all may be true but i clearly received a significant decrease in knocking and surging after the changing of the o2 sensor.

 

how do you go about cleaning the egr valve? is it a complicated process?