Opinions please about my prob

[srteach]

I have an idea of what might be wrong, but I want unbiased opinions.

The problem:
The throttle will not back down in most deceleration cases. When I release the throttle to decelerate, the throttle will most times stay at the last RPM speed (clutch in or out). i have to come to a complete stop and slap the throttle pedal before it drops to idle RPM. It then will idle at about 450RPM (book spec idle is 750 to 800 RPM).

On start, it will usually die unless I use the throttle to keep it running (warm or cold engine).

I believe that the IAC valve is not working properly. (IAC has been cleaned many times.) Am I right or wrong? Opinions? Other things to check?

 

[KELLY88]

Sounds like the IAC would be a good place to start. Also check for vacuum leaks and inspect the MAF sensor.

 

[Ozwynn]

it helps to know what engine you have.

star here. http://www.fordfuelinjection.com/ this site is for V8s but it does a really good job of explaining how to troubleshoot ford (EEC) EFI

most of it applied to EEC4 but the processes and test procedures for the components are the same.


I would look at the IAC, and the VSS...... I don't think you have a TFI but I don't know alot about OBD2

 

[Will]

See if this helps.

I don't think it's faulty--maybe it is. It's likely the engine controller is fighting some other problem and that is just a symptom. It could even be the ignition advancing like crazy for some reason. I've never messed with an OBD2 but usually I run the codes and test each component that is indicated, like on that sheet I attached. Then I test the vacuum because the engine might be fighting an intermittent vacuum leak--put a wrench on the intake manifold bolts as well to see if there is an obvious loose couple, then the rail pressure just for grins. After that, I would start testing other compenents, even if they don't make sense. The throttle position sensor, the MAF meter and the O2 sensor seem like things that could effect the ignition advance or IAC decisions. I can scan more sheets if you need them. I don't guess your parts would be that different.

 

[srteach]

Sorry, BDAB, I forgot to include the info. Here it is...
99 Ranger, 4.0 OHV, 4x4 M5D trans
I have no vacuum leaks, Kelly88. Thanks for the advice
That does help, Will. Thanks, I will check everything again. And thanks for the scan, too.

I knew you guys would give me some clues. I appreciate the time you took to answer. I'll let everyone know what I find.

 

[srteach]

update

The IAC appears to have passed the testing from the scan (Thank you, Will).
I have one lazy O2 sensor, don't know if it would cause what I'm seeing, or if it is normal for that particular O2 sensor.
The TPS is showing 17% when the problem occurs, I don't think it is out of range.
I'm still looking...

 

[srteach]

Resolution

I started getting an OBDII code showing IAC valve underspeed. I would erase the codes and it would instantly come back. Since I couldn't find any other cause for my problems, I replaced the IAC valve (even though it tested OK). The truck runs great now. All stated problems are gone, along with some unrecognized ones.

The IAC was bad.

Will, you were correct. The timing was advanced at idle to ~25 to 32 degrees BTDC. IAC replacement fixed that as well. The lazy O2 sensor has corrected itself. Fuel pressure was and is at 34PSI, no vac leak found.

 

[BlackBII]

Glad to hear you got it fixed!

I was going to say, if the truck stays at the last rpm with the throttle closed, the air has got to be getting in there somehow, and the only somehow is the IAC, if no vac leaks are present.