ok so I had a long holiday weekend and now have time to dive into this situation again. I removed the IAC and cleaned it very well and reinstalled it. So now when the engine is started up cold it idles at about 450 500 rpm which is where I believe it should be. After a very short time of driving it hangs out above 1000. This is with the IAC UNPLUGGED!!! If the IAC is plugged in it is always about 1500RPM or higher. any thoughts

 

Sounds like gummed up TB. Also, check the TB shaft and linkage. After the truck has warmed up, and it is revving @ higher RPM, try manually actioning the TB shaft with the linkage. If you open it really quick and let it swing back, does the truck appear to slowly rev back down? Also, try to keep the TB lever pushed back after letting it swing back and see if the idle returns to normal. If it does, I vote for a worn TB ro weak springs for the linkage and TB shaft. I had a similar problem that a new BBK TB fixed. The springs on the TB shaft connecting the butterfly's were weak and wouldn't allow the butterfly's to close completely unless I snapped the accelerator pedal quickly. Also, there are "Wear Points" in the TB where the butterflies open and close on the shaft. After many years and driving, the sealing of the butterflies is not what it was originally.

As RLA2005 mentioned, a bad TPS can give similar symptoms.

When you pulled codees, did you use a Code Reader or use the paperclip? Either way, did you perform the KOER "Key On, Engine Running" test? This may cause the truck to throw a code relating to the problem.

 

ok checked all linkage and cables everything fine started over with all electrical tests and found that the TPS has the right voltages just backwards ex. at idle should be .50 volts and it reads 4.0-5.1 where as at fully open throttle it should read 5.0 volts and it reads .50 weird huh i will replace TPS tomorrow and see what happens?

 

did you find anything with the tps? my truck has the same issue. idles too high. 1000 rpm cold and 1200 warm. idles down to 800 with a/c on. idle air contro unplugged doesnt affect it. swapped throttle bodys, iac, tps, checked every vaccum line for leaks and fixed leaking egr vaccum line. im stumped. sick of this high idle. let me know if you have any other ideas.btw i have no codes

 

ok replaced TPS with one from junkyard. Everything checks out volts ohms etc. NO CHANGE. This is aggravating me bad now what else could it be?? If i unplug the IAC there is subtle change when engine is warm but leave it off and it idles at over 3000 rpm Could the IAC be bad after all?

 

I swapped out my iac today and now it idles down. My old one moved freely and I'm not sure what was wrong with it but a used one fixed it

 

im going to the store to buy a new IAC right now I dont know what else to do Ill let you know in about an hour

 

ok put new IAC on still idles high but now it surges between around 1650 rpm and 1000 rpm. Sorta in a slow manner like idles at 1000 for 10 seconds or so then jumps up to the higher value for 10 seconds or so and just keeps doing this

 

searching through different forums i found a lot of people with surging idle problems and one gent' that found a cure to it all. A spacer between the TB and the IAC??? with fine adjustment screws. Could it be as simple as that? And.... why did I not have this problem before with no spacer?

Help

 

That part was for truck's and perhaps cars made before the "Sludge-Tolerant" design was implemented for the TB's and the IAC would become gummed up. (Someone correct me there if I'm wrong) That block spacer with adustment screws will run you about $67 from a Ford dealership. I bought one for fine tuning my BBK TB but I believe I will no longer need it when I'm done with my 302 rebuild.

Personally, it sounds like an unmetered air leak/vacuum leak. I know you have probably beat this idea around enough that it doesn't apply. Did you try to remove the PCV valve rom the rear passenger cover and cover it with a piece of heavy weight paper. See if the idle condition improves. I have some other thought, but let me know what you think of the above.

 

Ok ill go try it right now. i would think Vacuum leak as well but I just cant seem to locate one

 

well I tried plugging the PCV. No change What other tricks do you have. Im stumped. where are the most likely vacuum leaks I had to remove the upper Intake and TB but as near as I can tell these have no leaks gaskets were in good shape and i cant hear any leaks nor does spraying cleaner around seal do anything and when i cover the TB intake ports it acts starved for air.

 

I'm still stumped. My other ideas are to reconnect the IAC, disconnect the MAP sensor, and pull neg. battery cable. Let PCM reset. You said that you changed the MAP sensor. Ok, let's reinstall the original one. Verify there are no vacuum leaks. This means that lines running to the passenger side fender wall that activates the blend door. Look carefully @ everything that was touched during the repairs you made a few weeks ago. I know there is a cluster of vacuum lines that run behind the plenum that are a complete pain. Are you sure they are properly connected and are fully intact. As I mentioned earlier, did you notice clean closing of the throttle linkage when you opened and closed it? Verify that any vacuum line running to a Vacuum Reservior(Coffee Can) is working prperly and that the (Coffee can's) are not rustied through. If the one under the Driver side headlight is rusted thru, you will have a consistent vacuum leak.

My last thougths are; The TB set screw appears to be set incorrectly; When you had the TB off, did you disconnect the TPS? If so, did you Matchmark it's relationship with the TB before disconnecting it? If the "Tangs" are set incorrectly, it will hunt for the correct reference point. I found my TPS ran well @ .79-81 volts. If you reused gaskets, there could be a leak. That's what I have found with reusing old gaskets, especially if they are more than a year old. Not saying there is, but it sounds like you covered the basis for trying to find a leak spraying cleaner around the areas. Last thought, when you had the plenum off, did you aso remove the lower intake manifold? If you did and you didn't replace those gaskets, chances are it's leaking there. If you didn't use a torque wrench for tightening down in the correct sequence, that may also be giving you problems. I don't think you had it off, but just checking. I will look later for the TSB from Ford concerning High Idle problems and post here.

That's all I can think of now.

 

I've included this link concerning high idle problem/setting idle.

1983 Ford Bronco Diagrams picture | SuperMotors.net

 

Thanks of all the things to happen today. First a horse escaped the pasture and i had to mend fences. The tranny in the wifes burb decided to loose all its fluid and i just barely got home and havent had a chance to even look at the F150 with its annoying now surging idle. But tomorrow is a new day Thanks for all the help and thought I will keep you posted.

On a side note does anybody have any insight good or bad on a 03 Excursion V10 EB??