high idle after drive

[dagenham]

After driving about 50 miles or so last night on the highway at about 65mph I pulled off the highway down the ramp and the car would not come down to idle. It was way up at almost 2500 rpm.
I pulled into a parking lot went into the store for about 20 minutes to half hour and when I came back out it was still doing the same thing.
I got it home and did a quick check on the tps and it seemed to test fine. This morning with it being cold I retested the tps and got the same readings. I warmed the car up and it idled right where it is supposed to.
I pulled the iac off and it looked kinda nasty inside so I cleaned it out with some carb cleaner. I am wondering if it was gummed up just enough to be sticking when it was warmed up good and the throttle was held there for a long period.

Anyone have any other thoughts on what the problem could be???

[MikeFleming]

Got any EEC codes??

[Stinger]

That's typical behavior for a stuck/dirty IAC solenoid, though high TPS voltage will occasionally cause a similar problem.

[dagenham]

Mike, forgive me for sounding dumb but where is the plug to hook up the code reader?? I looked in by the master cylinder and couldnt find it. Is it located somewhere different than the newer foxbodies???

Stinger, the voltage for the tps is right where it should be from low to high.

[MikeFleming]

The EEC Self-Test connector is under the coil cover in front of the LF shock tower.

[brsvo]

What's a coil cover look like?

[caroth]

Vacuum leaks can also cause high idle, check all of your hoses. There are hoses heading over to the egr and pressure switch above the turbo and get brittle from the heat of the turbo.

[dagenham]

I thought about a vacuum leak also but it idled like it was supposed to the next morning.

[dagenham]

Well, I thought I had the TPS issue fixed but I was apparently wrong. I drove the car about 40 miles at highway speeds Saturday morning and it ran perfect with no issues. In the afternoon I drove it back home and it started the high idle problem again. I checked a code reader and all the codes basically pointed to the tps. I checked the tps and readjusted it and it ran good but I didnt take it for a long trip on the highway.
Anyone have any other ideas???

[Jack B]

To brsvo : the coil cover is just a piece of plastic that covers the coil to keep out dirt. It bolts over top the coil on the drivers side shock tower. This and along with most 5.0 distributor boots usually are never re-installed once removed. Here's a pic. They most often get thrown away (like the boots) over time. $T2eC16dHJIQE9qUHuFOYBRWRg4Fy3!~~60_57.jpg

[brsvo]

So that's a coil cover-both of my cars are missing them.

[MikeFleming]

If you got a code 23, replace the TPS.

[dagenham]

Yeh, thats what I was afraid of. When I checked the tps with a multimeter it was reading .90 instead of .91 and I had a heck of a time to get it adjusted to the .91.

Where do you recommend to go for a good one??? Are they still available from Ford???

[Meotchh]

NAPA, Rock auto, O-rielly ...

[MikeFleming]

Yeh, thats what I was afraid of. When I checked the tps with a multimeter it was reading .90 instead of .91 and I had a heck of a time to get it adjusted to the .91.

You're only measuring one point.

Code 23 means that somewhere in the sweep of the TPS it went open.

The TPS is a round plastic housing that has a resistive element on the inside diameter and a rorating wiper on the shaft in the center. As the throttle moves, that wiper moves across the element on the outside. As the TPS husing nad element heat up, they change shape. So anytime that wiper does not make contact with the element, there is no signal to the EEC. This sets a code 23.

So for the rest of that key-on cycle the TPS is ignored. A few things arel oist when there is no TPS signal: there is no WOT fuel enrichment; the WOT timing tables are never usedd, and closed throttle is never detected (used to control deceleration and idle speeds. So the "idle" hangs around 2000-2500 RPM.

Many years back I took a TPS housing apart to view the internal pieces and see how these problems come about. If only I had a camera then. Sigh.

Usually a quick EEC reset (key to off, right back to On) will clear the issue. until the open spot is detected again.

You might be able to see the open spot by measuring the whole sweep range with a DVM. Look for any uneven jumps in voltage. When it's hot.

ALL afermarket TPS units have a one year (minimum) warranty.

[dew34]

I had a high idle issue that I chased for a few weeks almost like the issues you are having. I did some searching and found some info that steered me in the right direction. I don't remember word for word what it said but basically was that if the tps has any kind of loss of signal it will raise the idle to keep the motor from stalling at an idle . So I checked the tps voltage on both sides of the tps harness plug. On the tps side of the plug the reading was good through the range with an analog vm but on the other side of the plug every now and then I would get a slight blip of the meter needle while going through the range. While it was running at an idle I took the tps plug and started moving and shaking it while doing that I could get the idle to raise up over 2k. Turn the key off start the car it idled fine till I messed with the tps plug. So before I opened up the harness to ck for damaged wires I pulled the plug apart I checked the plug both sides for damaged connectors found no damage, bent pins or connectors that were spread. I next washed all the dielectric grease from both plugs and looked for any corrosion found non washed both plug ends with contact cleaner. Next I put just a small amount of dielectric grease put the plug back together tested it again no more problem. I tested it again 3 or 4 more times pulling and shaking just as before no more high idle. The idle has been great for a few weeks. hope this helps. mike

[dew34]

Mike when I tested tps voltage with a DVM I could never pick up that little blip I described. But I could find it with my good old analog volt meter. mike

[MikeFleming]

Yes, MUCH easier to see anomalies using a sweep type meter. They're just not very common these days.

A little trip to the shop, a sacrificial part and a small jewelers cut-off wheel. hehehe

Some pics of the internals of a TPS. The tabbed thing in the center is spring loaded and rests against the flat end of the throttle plate. Note the small square hole where the round (shiny) return spring hooks on the top left.
Img_0224.jpg

Here's a shot of the wire side cut down to show where the wires connect. The left and right (VREF/GND) go the ends of the round part. The center one (TPSSig) goes to a flat, copper center contact plate. More pics later.
Img_0236.jpg

A portion of the plastic housing cut off. Note the spring in the center and the flexible carbon film to the right. That exposed pin has the black wire connected to it.
Img_0241.jpg

That protruding pin at the top of the pic is one end contact that touches an end of the carbon film. The carbon film has pulled away from that contact pin as the housing is no longer there to maintain it's shape. Good shot of the TPS return spring.
Img_0244.jpg

The cut-off section of the housing with the film and spring guides.
Img_0245.jpg

Another shot of the carbon film and where it contacts one of the end pins. That end pin connects to the EEC Ground (black) wire.
Img_0248.jpg

Here we see the carbon film stretched out and the center rotating part with the wiper arm that contacts the film.
Img_0249.jpg

A better pic of the wipe that contacts the carbon film.
Img_0251.jpg

Center thingie with wipes and return spring removed. That wiper contacts the carbon film that runs around the inside of the TPS body.
Img_0253.jpg

The other side of the center thingie showing both wipes. The 2-tip one brushes against the flat copper arc plate (pics later) which connects to the center TPS signal wire. It is the same piece of metal that contains the wipes that brushes the carbon film rivited to the plastic center rotating piece. No bearings.
Img_0258.jpg

Carbon film showing wipe wear marks.
Img_0259.jpg
Img_0260.jpg

Flat copper arc plate that the two-tip wiper arm brushes against. It's connected to the center TPS signal wire.
Img_0260.jpg

Any dirt can foul and/or wear the carbon film and result in intermittent contact. Heat-warping of the plastic body that is supposed to keep the carbon film flat and even can also cause intermittent issues - related to temp. Lastly excessive vibration can cause wear in the carbon film and give intermittent contact.

Naturally we have the most vibration-prone engine Ford has ever made.

[Meotchh]

Mike when I tested tps voltage with a DVM I could never pick up that little blip I described. But I could find it with my good old analog volt meter. mike

Sounds like the DMM you were using doesn't have enough resolution to accurately display the minor fluctuation you were trying to view. An analog meter will normally show this better as the needle will show a more visible deflection when the dead spot is found.

[Meotchh]

Anyone here have access to an xray machine for multi layer circuit boards? We used them in troubleshooting manufacturing issues in cellular manufacturing. It would be interesting to see an xray pic of the TPS rather than the destructive pics Mike posted.