'02 ST XLT 4.0 4x2 5-spd Manual - RPMs racing

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LV STr

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Good evening folks,

I'm a long time voyeur on here, but this is the first time I have posted. I bought my ST new and have driven all but about 150 miles of the 193,000 miles it has on it. It has been a wonderful truck and I try to take care of it myself as much as possible. Mind you, I am no mechanic, but can be handy enough to be my own worst enemy. I have done much of the work, which thankfully hasn't been much that was needed. I'm hoping that you folks might be able to help me resolve an issue before I have to take it to a professional.

Last summer, when the truck warmed up (a laughable understatement in the Las Vegas heat) the RPMs started racing to about 3K when the clutch was engaged and stayed at that level. If I allowed the truck to slowed down while in gear the RPMs would come down, but as soon as the clutch was engaged the RPMs would race back up to 3K. I was given the advice to add a fuel injector cleaner to the gas tank to help clean the injectors. I was hesitant at first as years ago I'd heard that this would only damage the injectors. After much discussion, I was convinced that the quality of the cleaners had improved and no longer posed the same problem. This seemed to correct the issue.

As the weather warmed up again this year, the issue reared its ugly head once again. I tried the same remedy, but it has not helped. The last gas tank yielded about 14 mpg where I used to get about 18 mpg.

After reading other posts on different but related issues, I plan to clean the MAF sensor and IAC valve this weekend. Would anyone have some advice for a novice on what else I may try to do to address the problem? I thank you in advance for any help you can provide.
 

swshawaii

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Unlikely your 3000 RPM engine racing issue, but throttle body cleaning should also be included in regular maintenance, Dirty throttle bodies are known to cause a sticking throttle, but shouldn't cause racing. Also recommend using specific CRC throttle body cleaner instead of much harsher carb cleaner. Link below.
Untitled Document
 

LV STr

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Thanks, SWS. I certainly can’t say that it’s part of my regular maintenance, but I have cleaned it on occasion and as recently as a couple of months ago when this started up again. I will give it a more thorough cleaning this weekend and I’ll pick up the CRC throttle body cleaner per your recommendation. I appreciate your input.
 

LV STr

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Thanks, SWS. I certainly can’t say that it’s part of my regular maintenance, but I have cleaned it on occasion and as recently as a couple of months ago when this started up again. I will give it a more thorough cleaning this weekend and I’ll pick up the CRC throttle body cleaner per your recommendation. I appreciate your input.
Hey SWS,

Following up…I removed the throttle body and gave it a thorough cleaning. It appeared to have done the job that first week. These last couple of days, the RPMs hold at about 2,200 for a couple of seconds when I engage the clutch and then a very slow decline to around 1,100-1,200 RPMs. About half the time, it’ll drop below 1K. The normal idle used to be appx 850-900.

Should I replace the throttle body? It’s the original and I don’t know if they go bad. Or, is there something else I should look at?

Thanks again for your advice on the matter.
 

swshawaii

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@nevadabob9mm
Archived projects from Todd Z's old site.

@LV STr
Good to hear throttle body cleaning somewhat helped. I assume you have a 2001-05 (Gen1) Sport Trac since you have manual transmission. See no reason to replace the throttle body since it's NOT electronic throttle control like the 2007-10 (Gen 2) and has a serviceable idle air control valve. You didn't mention if you have a check engine light or stored trouble codes.

Here's a simple IAC cleaning project if you haven't cleaned it yet.
 

LV STr

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Thanks for the quick reply, SWS. I went ahead and cleaned the IAC and the MAF, along with the K&N air filter when I did the throttle body. The throttle body certainly seemed to be in good condition and the ST is definitely running much better. I’m just hoping to get that last bit of “racing” and idle down more.

It’s not throwing any codes nor is the CEL on.

She’s been a great truck and I’m trying to keep her going as long as I can.I’ve run Castrol full synthetic and upgraded oil filters from the beginning.

Thanks again for your help.
 
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