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post #1 of 8 (permalink) Old 11-26-17, 10:28 AM Thread Starter
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engine idle, revving issues

Hello all,
I have a '99 2wd w/the 2.5 I4 engine, manual trans. The past few years, when the weather changes (Chicagoland), that the engine will rev up when I am shifting gears or shift to neutral when moving. It can go as high as 4000 but seems more common to go up to 3500, and will come back down after vehicle has stopped a few seconds. This year I noticed the idle was higher than usual-I have adjusted the screw on throttle body to try and lower but issues remained. The idle seems to change often (when sitting) following compressor clutch engaging and disengaging, which also happens very often. Also the throttle position sensor seems to go bad every 6 to 8 months. After trying to resolve issues at home I took it to my usual mechanic. I was told to replace the IAC and PCV because they were throwing off the fuel trim levels. So I replaced the TPS, IAC, and PCV with Ford Motorcraft parts; cleaned throttle body and replaced gasket; and replaced a couple vacuum hoses that were leaking or worn. This resulted is the truck running fine for a week or two before it reverted back to old symptoms. I have gotten check engine codes for TPS (a) low voltage and (b) intermittent and IAC circuit low. Recently I have also had trouble keeping my own reader connected, now this may because it emits a Wi-Fi signal to my phone, but it has become more difficult just to connect and yesterday I could not get it to work without disconnecting the battery and allowing everything, including codes, to reset. Upon having engine codes checked by local parts store, the person said that something may be wrong with the PCM because codes the codes were for new parts, the truck was running fine, and his reader said it could not finish its scan (unsure if this means anything). I don't believe I have any vacuum leaks, there is a very small coolant leak on a heater line, and no other mechanical issues. Plugs and wires were done over summer.

What am I missing, have I overlooked, can I check or replace at home? Can this whole thing be caused by the PCM? Given that I have adjusted throttle body screw how can I get it back to where it is supposed to be?

Please keep in mind: I am trying to keep costs down by doing as much myself possible, but I am novice to say the best with limited tools, experience, and expertise but due to an injury at work a couple months ago, I cannot afford a mechanic again.

Thank you for reading and replies,
Adam

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post #2 of 8 (permalink) Old 11-27-17, 03:52 PM
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Re: engine idle, revving issues

I can give you the method for the base idle on the 5.0, it should be the same for the 2.5, disconnect the battery for about 30 minutes, disconnect the IAC, then start the engine. Adjust your idle to (I believe) 800 rpm. Shut down the engine, reconnect the IAC, turn on all of your accessories, start the truck and let it idle for 2 minutes. Turn it off again for 2 minutes, then turn it on again for 2 minutes, always letting it idle. The accessories should be on the whole time.

You still may not be out of the woods with vacuum, I find it's best that is one vacuum hose needs to be replaced, they all probably do. Do you remember specifically what the codes were (P0XXX or P1XXX)? Can make a bit of a difference on how it's looked at. Given the age of the truck, check your grounds, particularly on the PCM. If you're unsure, it won't hurt to add a ground... as long as you're adding to a ground and not accidentally putting a ground on a line intended for voltage.

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post #3 of 8 (permalink) Old 12-05-17, 07:59 AM Thread Starter
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Re: engine idle, revving issues

Thanks for the reply! I haven't tried your suggestions quite yet, but I received a suggestion from a hot rod friend that I remove and check my EGR valve, something I had not yet considered. Upon removal and bringing to light, the inside was completely caked with carbon. I used a gasket pick to softly remove some of the graphite like material and then tried to gently press the valve to see if it was stuck, and it was. I cleaned more from both sides of the valve as best as I could. It was now able to be moved just by one's own lungs. I did that 3 days ago and have not had any of my previous problems. Idle is constant (unless using heater), engine does not rev up abnormally high when shifting, and the check engine light has not yet come back on.

Thank you for you suggestions,
Adam
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post #4 of 8 (permalink) Old 12-05-17, 09:24 AM
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Re: engine idle, revving issues

Thanks for updating the forum , may help others .

Never, never, never give up.
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post #5 of 8 (permalink) Old 12-05-17, 03:50 PM Thread Starter
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Re: engine idle, revving issues

Hello all again,

I may have bragged about solving my previous issues before I had the time to observe the temperature change here in Chicagoland (yesterday-60 high and today- down to 30). Today the engine reverted to revving when shifting gears. Seems most prominent when clutching to, up or down, shift from 4th. But it does happen within other intervals. I was able to notice power level changes when I heard the compressor clutch engage or disengage-not abnormal, but the timing seems as though there may be a correlation. I must still be missing something. I had hoped this would allow me to stop buying premium to stop engine knock but it is occasionally audible while cruising, but mostly when clutch is being reengaged.

Is my idle off? Did I miss something on the intake? I have been suggested timing belt, tensioner, and pulley(s) as a diagnosis based on hearsay but I am not sure how to support that diagnosis within my own capabilities. What else could be the problem? I have a hundred questions, but I'd rather participate in a discussion. I am going to write the manufacturer of my OBDII reader to try and solve its connectivity issues so that I may be able to read more technical aspects of the engine, but please post any and all questions, experience, advice, or expertise.

Thanks again,

Adam
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post #6 of 8 (permalink) Old 12-05-17, 04:13 PM
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Re: engine idle, revving issues

Still would approach with what I approached originally. If your EGR was that fouled, your intake maybe as well.

Ever notice that there's so many high performance parts available for GM products?

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post #7 of 8 (permalink) Old 12-05-17, 04:29 PM Thread Starter
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Re: engine idle, revving issues

To what extent? I cleaned the throttle body-not perfect but much better than before especially what I could see toward throttle valve. New gaskets on throttle body, iac, and EGR. And to answer a previous question the code that comes up most P0122 TP sensor circuit low input-to which I have replaced the sensor multiple times with aftermarket (auto stores) part as well as recently a factory Motorcraft sensor. To this issue I have been recommended replacing the "pigtail" connector for the TPS, but I am again unconvinced because in a controlled environment it does not occur. Even though I have wiggled and pulled the wires with engine running to no difference in how the engine runs.

Thank you Cat and Logan for continuing the conversation

Adam
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post #8 of 8 (permalink) Old 12-05-17, 05:13 PM
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Re: engine idle, revving issues

Here's a procedure for testing the TPS. In the end it discusses the throttle adjust and how it can affect you. On the 5.0 instructions, they mention loosening the TPS slightly and shifting it until you get the .9-1.0 VDC at the idle position, they don't mention that here. You might first try to adjust the idle screw to see if you get the correct voltage.


Part 2 -How to Test the Throttle Position Sensor (2.3L Ranger, Mustang, B2300)

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