Hi! This forum has been a blessing troubleshooting the high idle on my 1999 Ford Ranger. My mechanic and I agree we need a new throttle body (Part # F87Z9E926DA). Unfortunately, it is no longer being manufactured and I cannot find a replacement.

I have read there is a teflon(?) coating on the inside that helps to prevent airflow around the butterfly valve. Does anyone have any ideas on how to add the coating or where I might look for a good replacement.

Thanks for your help.

 

Did the high idle appear suddenly or has it been creeping up on you?

The IACV is a more likely cause, or a vacuum leak. You can't add the coating, and it is not likely the cause either. Has the throttle body bore been cleaned? The Teflon coating is there to help it stay clean, the carbon doesn't stick to it well.

Has the IACV been checked? They get gummed up and stick open apparently.

1999 doesn't have the high-tech electronic throttle bodies. They're pretty basic. A mechanical blade, a blade position sensor, and an IACV to control idle speed.

 

Thank you for the feedback. I have replaced the IACV, throttle body sensor, all three O2 sensors and all six injectors. One of the injectors was completely clogged. My mechanic has cleaned the throttle body. The high idle is not as bad as it was but I believe it is caused by the throttle body sticking just a bit.

The truck has 287K miles and still runs strong. Quite a few people have told me that air can squeeze between the side of the throttle body and the butterfly valve causing more air to enter then engine than commanded. The IACV should compensate somewhat for the leakage. I have had two mechanics look all over for a vacuum leak (even smoked it) and they can't find any leaks.

I understand the throttle body is controlled by a spring assembly. Any chance I could replace the spring on the butterfly valve?

I had two codes before the injectors were replaced. He also replaced the IACV at that time.
P0171 - System to lean bank 1
P1506 - Idle air control overspeed error

I appreciate your response and help.

 

Since the throttle blade is mechanical you should be able to close the blade by hand. If idle speed drops you'll know it's sticking. Just push the opposite way that the cable would pull. See what happens. Who knows, an extra return spring might do the trick. I don't know the return spring setup on these TB's but that has worked for me on other vehicles, that had an internal TB spring and an external spring on the linkage. It might even be something unusual like a sticking throttle cable. The hand test should tell. Maybe it just needs some lubricant.

I think that the second code means that the PCM is telling the IACV to close to drop idle speed but nothing is happening. You might try unplugging the IACV and starting the engine. Idle speed should be very low, maybe even causing the engine to die if the IACV is closing correctly.

As far as the P0171 code that's usually a sign of an air leak. If you can see live data it will show up in fuel trims as extra fuel, positive trims. If your idle speed is high but your fuel trims are correct it's probably not an air leak from an external source.

Those are just things to do that might give you more ideas. You said that you replaced the injectors but didn't say if that was to fix the high idle or for some other reason. A clogged injector should have given a dead miss. Was there a miss and a high idle? Not sure it matters, just curious.

If it was mine I might try a wrecking yard throttle body. They're not really an item that fails often as far as I can tell. Probably why they're hard to find. Good luck.

 

The truck did seem to have some misses here and there. It is running really nice after the mechanic. I did think about a cable issue. Right now it is idling around 850 RPM and the throttle is only sticking a little bit.

Before the injector replacement, the high idle would appear anytime I took my foot off the gas and coasted to a stop. The high idle would only stop after 10-15 seconds stopped at the light. It would idle around 1100-1200 RPM. If I revved up the engine while stopped it would take the 10-15 seconds to come back down to the 1100-1200 RPM. The fuel trim was high before the injector replacement but it now seems fine. I don't know what it involved in an injector replacement but if the mechanic had to repace any gaskets would that cause an air leak?

 

There are o-rings on the injectors that can cause an air leak. They would lean out only the cylinder that had the leak though. Might cause a miss, could cause a rich code as the unburned fuel makes it to the sensors.

You're describing a hanging idle, not typically caused by a vacuum leak. A vacuu leak would just stay high, it wouldn't slowly drop. Sounds more like sticky linkage or throttle blade. But you should be able to reproduce it in the driveway. Get it to rev high then force the throttle closed by hand.

On the other hand though I had a Pathfinder that used to do that at times. I think that it had something to do with the EGR system. Supposed to close at idle but didn't always do it. Can't remember exactly what the cause was.

Idle conditions are their own special things. I think that even the EVAP system shuts off at idfle and only opens when the engine is at higher RPM. If your throttle body and IACV function seem correct you might move on to those other things that only happen at idle.

 

Here's a description of the 2003 F150 EVAP system. They've all been like this for years, across brands. Just a possibility. Might not set a code because it fixes itself.

The vapors are purged from the canister by allowing the engine to suck air through the canister. Basically a controlled small air leak in to the intake system.

 

Welcome to FTE.

You've been busy on this one & there are some important unknowns & more no cost or scheduled maintenance replacement items & trouble-shooting things you can try to see if you can get a positive response.
Might be helpful if you'd post the engine, tranny, drive-4X2 or 4X4 & body type as they can have things to look for that'll affect idle speed. Also post where the vehicle is on its Scheduled Maintenance replacement parts list for things like O2 sensors, PCV valve, Mfgr of the IAC, & spark plugs if they've been replaced as its important the plug design be considered for our Waste-Spark ignition that works the plugs Twice as often as the old distributor-coil system.

With the mileage you've posted, the PCV valve is Way over do for replacement. Just because it'll rattle when shaken just means its not mucked up solid inside, with the posted mileage a shake test doesn't measure how weak the spring, or worn the pintle & its seat inside is & as its downstream of & not monitored by the MAF sensor, so if bypassing air it' can muck up idle. Thus, time for a new one if not already done. Same for the air filter, as both are overdo & on the Scheduled Maintenance replacement list & can affect idle & fuel trim.

Also, since the fuel injector work & one was clogged & not squirting, the fuel trim tables were corrupted & that cylinder with the faulty injector had been running Lean & likely hot, so you may have a burned valve or seat on whichever cylinder that was in bank 1??? If you think that's a possibility you could perform a scan-tool cylinder balance test & if it flags a cylinder, then perform a compression test on that cylinder to see if that'll offer up a clue.

In case the shop didn't disconnect the battery B- lead when working & then didn't perform the cold & warm idle relearn, maybe do the battery disconnect & the cold & warm idle relearn yourself as described here. If you have a straight drive, no need to the shift into each gear like needed for the auto-tranny. Be sure to turn off all electrical loads like fan, lights & A/C when doing the relearn as outlined here high idle problem - Ford Truck Enthusiasts Forums (ford-trucks.com).
More thoughts that have come to mind for pondering, let us know what you find.

 

The truck is a 1999 Ford Ranger XLT 6 cylinder 3.0L flex fuel - 1FTYR10V1XTA
I had an exhaust manifold leak where the gasket failed. I got the gasket replaced but that was after this problem surfaced and didn't fix it.
O2 sensors were replaced in Sep 2023. I added a throttle body gasket (it wasn't originally there in Nov 2022. PCV valve was changed in Oct 2022.

The PCV valve was purchased at Autozone. I needed to press on the 90° plastic tubing as it wouldn't just snap on. I assume that is to ensure a complete seal so no air can escape but I was surprised at how much was needed to get the elbow to attach to the PCV valve.

I do have scantool data from a baseline I took in 2011 and what I just took yesterday as well as the high idle data in 2023.. It is in an excel spreadsheet. Sheet #1 has the raw data. Sheet #2 has a graph and you can select which value to see from cell B2. Both were taken with the truck at idle. On sheet #2 select cell B2 and a drop down icon appears to select the data you want to display

I have the shop manuals and will look at the evaporator emissions canister. I have never replaced it. I have replaced the EGR and DPFE in 2011. From my understanding, a clogged EGR shouldn't cause any issues at idle because it is typically closed. If it was open, it would cause the idle to drop and perhaps stall the engine. Am I missing something?

I do appreciate the responses and advice. It is quite a puzzling problem to me.

 

One of the basic elements of the PCM function is to maintain a steady clean idle. I think that is common across all electronic fuel injection systems since they were developed and introduced for the purpose of lowering emissions.

I don't know if a sticking EGR valve would cause the PCM to hold idle speed high or not. But the PCM will do whatever it takes to keep the engine running smoothly at idle. It's all about keeping the exhaust gases clean. Just one thing of many to think about. If your issue was a PCM control issue then unplugging the IACV would show it. The PCM would be holding the IACV open to keep the idle speed up.

Seems like you're kind of at the point where you can try some things then think about what happened after the results. Press on the throttle linkage, unplug the IACV. Whatever happens will tell you something. p.s. you can drive the truck with the IACV unplugged. You'll just need to control idle speed with the gas pedal. If it dies at the lights instead of hanging high that will be a good clue.

I found an interesting page from an online textbook about the concept, linked below.

https://www.sciencedirect.com/topics...-speed-control

 

I have verified the throttle body fully closes when I rev up the engine. I did find this to be interesting though I don't know what it means.

With a cold engine at idle, I removed the vacuum line from the EGR valve and observed no change in the engine performance. I would have expected this behavior as the EGR should be fully closed right now.
With the engine at operating temps and at idle, I again removed the vacuum line and experienced no change in the engine. I revved the engine up with the vacuum line disconnected and as the RPMs reduced there was no discernable change from a normal deceleration pattern. This may indicate a clogged EGR valve?

The long term fuel trends are still positive..


Scantool image for 99 Ford Ranger

Scantool data for 99 Ford Ranger

 

Probably not your EGR valve. I found a page from Delphi about them. I had had a different EGR problem on that same vehicle, a clogged EGR port. Never was sure of my high idle problem. Link below about EGR.

It is interesting that both banks are slightly high in trims, even compared to before the OBD test. What is the OBD test? 5 and 7% is well within normal range though. I assume that is engine hot? Vacuum leaks tend to be worse on cold engines.

On the throttle body closing, you didn't say if the idle was still hanging high. In one of your posts, #5, you said the basic problem is that it hangs high for 10-15 seconds but then drops back down. So you have the common intermittent problem. You need to find a way to reproduce the problem consistently so that you can understand cause and effect as you try things. Might have to drive around the block twenty times or up and down a hill, whatever causes the problem to happen every time. Intermittent problems are tough.

https://www.delphiautoparts.com/reso...o-troubleshoot

 

Come to think of it. I did the EGR vacuum test when the truck was idling normal. I also did the throttle check at that time. I did rev it up at the throttle body and the butterfly valve seemed to close with idle going back to normal.


The 10-15 seconds of high idle was before the injectors replacement. It is a lot better now but there is still a lower high idle than before.

I think I need to wait and let the computer relearn everything. I drove it around town today and was quite pleased with its performance. Only once coming to a stop about 15min into my trip did I notice the high idle.

The high idle is around 1500 RPM for a short period of time whereas before it was closer to 2200 RPM for 10 to 15 seconds.

The OBD readiness tests that are typically accomplished when the computer loses power were completed and it says there are no faults detected. Before the injectors replacement, the CEL would illuminate within the first 30min driving after a computer reset.

Let me try to reproduce it with a warm engine and do a throttle check.

I have never replaced anything with the evap system. From my understanding the evap system traps unused fuel and recirculates it back into the exhaust(?) to be burned, yes?

Arizona fuels are "contaminated" with ethanol during the summer months to help lower emissions. At first, the high idle would only occur during the warm afternoons driving home for 30min. As the problem.progressed it started occurring everyday and every time I drove it.

It is a flex fuel vehicle and I don't know how the vehicle knows the type of fuel being burned. I do know there is a fuel box attached to the underside of the truck that monitors that. I'm curious if that could be causing this issue.

 

You have a nice diagnostic trouble-shooting tool base to use, so consider concentrating on getting all the Scheduled Maintenance replacement items up to date. Like fuel & air filters, correct heat range & design - fine wire iridium enhanced center electrodes with platinum pad ground side-wire type spark plugs & Motorcraft plug wires for your waste spark, ignition & flex fuel systems.

Then maybe with the mileage on this puppy consider carefully cleaning the MAF sensor with a non-residual plastic safe spray recipe just for the purpose, like CRC MAF Sensor spray.

After all the scheduled maintenance items are up to date, perform the cold & warm idle relearn, all so you have as stable a base to work from as possible, so old parts aren't causing confusing variable inputs. I'd do a fuel pressure check after installing the new fuel filter.

If your scan-tool will do a power balance test & flags a cylinder, go there & perform a compression test & maybe a fuel injector check if that cylinder is on a cylinder bank with fuel trim problems.
EDIT: Let your scan-tool findings & any trouble codes be your focus guide.

More thoughts for consideration, keep us posted on findings.