Throttle Position Sensor starting to go?

Alien

Bought an X
Location
Gilbert AZ
So, I have noticed this twice now where I will drive the truck about ten minutes and everything seems fine. I get to my destination, put it in park, and it's idling at about 1250-1300 rpm. I goose the peddle and nothing changes. But, if I turn it off then start right back up, it idles normal. The engine is warm, so that's not the issue. Even when I first start it up it runs at 1250 rpm for less than ten seconds then it starts slowing down.

Throttle sensor is the first thing to make sense. I don't think it's the dizzy since the rpm's don't bounce around. Thoughts?
 

kirk

Butterfly King
Moderator
Supporting Member
Location
Allen, Texas
Throttle sensor and the distributor are always my first suspects when dealing with a low idle issue.

If not that, a dirty or failing MAF.
 
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Alien

Bought an X
Location
Gilbert AZ
Update - the RPMs run approx 1400 regardless if cold or at operating temp when in park. When stopped at a light with my foot on the brake, it runs 1000-1100 RPM. It runs smooth, no misfires or anything like that, and I have no acceleration issues.

Something odd from when my son my son driving it the other day, he blazed through over a quarter tank going 40 miles roundtrip on the freeway. When I filled the tank the next day, I calculated my MPGs at 14.79, which is really bad even for this. I normally run about 17 for combined city/freeway driving. My son isn't any more lead footed than I am, so I can't blame him.

I'm not sure the disty is the issue. I put my cheap OBDII reader on it and it reads the spark adv at 10-11 BTDC, mostly 11, and it doesn't vary.

I'm also not showing any codes. The only code I've had in the last few years is P0456 (small evap leak) and occasionally P0457 (very small evap leak), and I only get those when the tank is at 1/4 or less.

Any ideas why it would run about 600 RPM high?
 

RamblinRover

First Fill-Up (of many)
Could be a fair number of things. First thing I would check as it seems you have a scanner and can see engine data - There is usually a RPM reading and a desired RPM reading. See if the computer is telling it to run that fast. If the desired is 750 and it's at 1250 it would normally set a code but maybe not. You could have a messed up idle air control valve, vacuum leak, or even a bad temp sensor for the computer to name just a few. I believe this uses a different sensor for the gauge and the comp. so can't go off of the gauge as the comp is using different info. So look at that as well. - This is just an example but lets say the comp thinks the engine is at 15f it is going to run like a cold engine all the time and not go into closed loop. 15f is not an impossible number and is within the temp sensors normal range and so won't set a code. Newer cars will see this and say wait it's been running for 15 minutes should be warm now - older cars not so much.
 

Alien

Bought an X
Location
Gilbert AZ
Thanks. I'm leaning towards the idle control valve as the engine acts like one where the choke is stuck on the carb. I'm going to try cleaning it to see what happens and go from there. I'll also test the TP sensor to make sure it's good. I wish it would throw a code so I knew better where to look.
 

RamblinRover

First Fill-Up (of many)
One other thing I thought of. Did you look down the throttle body? Make sure you don't have build up in there holding the plate open. Usually when this happens I almost get a pop feel in the pedal on apply from it freeing itself but not always. Just trying to think of things the comp won't detect.
 

Alien

Bought an X
Location
Gilbert AZ
Yes, in fact I cleaned it Monday. I don't think it had ever been cleaned before, and I was lazy about doing it. It was filthy. Now that it's clean it's stained but there isn't any buildup holding plate open.
 

RamblinRover

First Fill-Up (of many)
I found a TSB NTB05-067 for idle speeds 25 rpms or higher than desired but wow it's a war and peace level bit of script - found it on a non pay site here TSB . It's for 2002 and later not sure what year your X is. May or may not help as a fair amount of it refers to consult.
 

Alien

Bought an X
Location
Gilbert AZ
Now that I have looked this part up, I realize I didn't get a good pic. In looking at the pic, I don't think that my fast idle cam is not in the correct position. After I put everything back together, I could manually rock the cam back and my idle would drop. The plunger(?) (orange arrow) does not connect with the screw (red arrow), which doesn't adjust the cam. It's difficult to see in the pic, but the screw is just slipping under the plunger. I didn't let it warm up though.

I'm thinking this is the source of the high idle issue. How to I test to see if I need a new plunger - "Element Kit-Thermostat"? Let the engine warm up and see if it extends? Am I looking at this right?

Looks like fun.


1647308745061.png
 

RamblinRover

First Fill-Up (of many)
Hard to say based off of a picture but looks like the plunger is way up to the point of being against that other shaft. The screw also appears to be bent out. I would expect it to be straight not angled like it looks like it is.

INSPECTION AND ADJUSTMENT

With CONSULT-II

1. Turn ignition switch ON.


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2. See "COOLAN TEMP/S" in "DATA MONITOR" mode with CONSULT-II.


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3. When engine coolant temperature is 20 to 30 °C (68 to 86 °F), make sure that the center of mark A is aligned with mark B as shown in the figure.
- If NG, adjust by turning adjusting screw.

Lock nut:
Tightening Torque: 0.98 - 1.96 N.m (10 - 20 kg-cm, 8.7 - 17.4 in-lb)


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4. Start engine and warm it up.
5. When engine coolant temperature is 75 to 85 °C (167 to 185 °F), check the following.
- The center of mark A is aligned with mark C.
- The cam follower lever's roller is not touching the fast idle cam.
- If NG, replace thermo-element and perform the above inspection and adjustment again.


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Without CONSULT-II
1. Turn ignition switch ON.
2. Check voltage between ECM terminal 59 (Engine coolant temperature sensor signal) and ground.


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3. When the voltage is between 3.12 to 3.52 V, make sure that the center of mark A is aligned with mark B as shown in the figure.
- If NG, adjust by turning adjusting screw.

Lock nut:
Tightening Torque: 0.98 - 1.96 N.m (10 - 20 kg-cm, 8.7 - 17.4 in-lb)


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4. Start engine and warm it up.
5. When the voltage is between 1.10 to 1.36 V, check the following.
- The center of mark A is aligned with mark C.
- The cam follower lever's roller is not touching the fast idle cam.
- If NG, replace thermo-element and perform the above inspection and adjustment again.
 

Alien

Bought an X
Location
Gilbert AZ
@RamlinRover It was definitely the high idle cam mechanism. I saw a video where a guy moved the cam by hand, but I needed pliers to do mine. I PB'd everything pretty well, and after a minute everything loosened up. What I think happened is that the cam froze, and the tab with the screw bent when the plunger pressed against it, which caused the mechanism to not work properly.

Since I PB'd it and the tab is bent, the spring flexed all the way forward and now the mechanism is disabled. It runs fine now with no high idle issue. I live in the Phoenix area and don't really need that, so there's no rush to fix it.

Thanks for the help!

1647551238555.png
 

MisterH

Bought an X
Location
Washington State
My '03 just got back from the shop for major repairs. Started to idle high at stops at 1300 and neutral at 2000. Going back to the shop Monday. I only put less than 200 miles since the repair. It had the most upper half of the engine taken apart, so hopefully, it's on the shop and not something else.
 
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