TPS Idle Issues - ref TSB00-3-5

[Entropy]

Refresher:
http://www.v8sho.com/SHO/High_Idle.html
http://www.v8sho.com/SHO/TSB00-3-5.html
http://www.v8sho.com/SHO/highidle.html
http://www.v8sho.com/SHO/TSB99SHOTPS.htm

What I am interested in learning:
1.) Have any of you folks seen any instances where the service kit 'failed' and the same symptoms came back (likely to have to replace the harness again)?
2.) As a corollary, when driving down the road at speed and manually shifting to Neutral, does Ford have logic built in to keep erpm bumped up a bit for a brief bit of time or until certain conditions are met? Maybe a better way of asking this is how quickly does erpm return to idle or near idle when shifting to neutral at road speed?

History:
This on is a 99'. Weather has become much cooler in the past couple of mornings. No codes. Thousands and thousands of miles ago, I replaced the TPS harness when this behavior began - instant fix with no known reoccurrence of the problem until yesterday. Exact same behavior just began again (high idle, erratic cruise speed, varying idle, passing traffic with no throttle input, etc). If the harness was still a $15 part, it would already be on order but it is now over $90 and that is a bit to salty to just 'try' without a proper checkup. I swapped in another TPS I had laying around, disconnected the battery, headlamp drain of memory, and tried again. It seemed to behave much better this morning (actually slowed down when lifting off the throttle) but seemed to still idle a bit high and 'hang' at engine speed before coming down. Sure enough, I backed into a spot at work, shifted to neutral, and she bumped right up to 2500 erpm (give or take) and just hung there. I shifted to Neutral a few times (5-10) on the way in when traffic cleared and noticed that engine speed would hang for a few seconds before coming down.

Any help would be greatly appreciated !

 

[Entropy]

...I forgot to mention that both old and new TPS voltage readouts at closed and wide open throttle were close (around .93V at CT and 4.7V at WOT with smooth transition) . I was using a paperclip- not a good piece of copper or similar - so that may explain why it was a hair low at closed throttle....but I would have expected a tall reading anyway for high throttle.... I swapped anyway in case it was an intermittent thing not showing up in the garage.

 

[tardboy21]

I've had this problem, but I do not have a definitive fix for you. Personally I disconnected the battery one night while I ate dinner, then disconnected the TPS connector, applied a little dielectric grease, popped it back on and reconnected the battery.
It's been about a month and a half and I have had the idle problem once or twice in that time, but not every other day like I was having.
It's not a solution, but is something cheap which you can test to see if it helps. If the problem gets worse for me again I will likely replace the connector unless I find a better solution or different problem.

 

[escortlvr]

Have you ever replaced or at least cleaned the IAC? Common Ford failure part, don't care what make/model the car is.

 

[Entropy]

Have you ever replaced or at least cleaned the IAC? Common Ford failure part, don't care what make/model the car is.

I have had this thought - can I assume cleaning is a thorough bath in carb cleaner?

 

[bacernate]

I had the same issue on and off with my 97, what i found is with the scanner hooked up the tps would stay .2 to .3 volts higher sometimes. Cleaned the throttle plate and problem gone. Seemed to notice it more when the ac would cycle.

 

[St Louis SHO]

Yup, clean the throttle plate and throttle body and re-check before doing anything else.

 

[escortlvr]

With Ford IAC's you have to use electrical parts cleaner because they use nylon gears/Seals inside and regular carb cleaner will deteriorate the plastic.

I would suggest a throttle plate cleaning as well if it hasnt been done. A little trade trick is to use an old toothbrush to scrub the throttle body. Try and use electrical parts cleaner for that too.

At the dealership level we clean the IAC while it's on the car via the bypass port on the throttle body. Either a scan tool is used or a Rotunda adapter to physically open the IAC for cleaning.

Below how you can do it at home. Just make sure the gasket re-seals after you're done.

http://www.ehow.com/how_4763388_clean-idle-air-control-valve.html

 

[SHOZ123]

When it is idling high disconnect the electrical connector on the IAC. It should die immediately. If it does not them it is sticking open mechanically or you have a vacuum leak.

To test for the sticking open when it is idling high with the electrical connector off tap the IAC with something. If the idle then come down it confirms a sticking valve.

 

[Entropy]

When it is idling high disconnect the electrical connector on the IAC. It should die immediately. If it does not them it is sticking open mechanically or you have a vacuum leak.

To test for the sticking open when it is idling high with the electrical connector off tap the IAC with something. If the idle then come down it confirms a sticking valve.

I do believe I have read this exact statement a time or two in searching the past couple of days! (All in good fun) It did choke when unplugged.

Some combination of cleaning up the throttle plate (a little carbon - but not much) and 3 beers time worth of emery paper/scotch cloth slivers/pipe cleaner massaging of the connecter terminals, with a healthy application of dielectric grease, seems to have solved the problem....at least for the last 36 hours or so... I never ended up making it to cleaning the IAC.

Many thanks for the help! The next round is on me.