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High Idle RPM (1991 Explorer)

Dancing Bear

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April 14, 2008
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City, State
Annapolis, MD
Year, Model & Trim Level
1991 Explorer Eddie Bauer
My 1991 Explorer will start to idle at a very high rpm (1500 to 2000), it usually idles normally, but will idle at a high RPM after a while of idling normally (sometimes a week or two of normal idle, sometimes just a day). While troubleshooting I noticed that when disconnecting the throttle position sensor, the idle goes to normal, and then reconnecting the sensor the idle is fine for some time again. I replaced both the throttle position sensor and the connector, but am still having this problem. Disconnecting the throttle position sensor and then reconnecting it with the engine running seems to correct the problem for a period of time (from a day to a week or two), but then back to the racing idle. Any input would be greatly appreciated.
 



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35Remmy

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March 4, 2008
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City, State
Binghamton NY, Hazleton PA, Northern NJ
Year, Model & Trim Level
'88,'99 Ranger, '00 EX
Did you ever disconnect your battery after you replaced the TPS (throttle position sensor)?

Is everything hooked up correctly? Is the vacuum line that connects on the underside of the throttle body connected?

Have you tried disconnecting your idle air control valve (IAC) while the truck is running? It's the top-most sensor, to the right of the TPS, connected to the plenum or upper intake manifold (same thing, different terms).

I always tell people, for instance and in your case, the truck is almost 20 years old. MANY things will start to go wrong after that long.
 






Dancing Bear

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April 14, 2008
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City, State
Annapolis, MD
Year, Model & Trim Level
1991 Explorer Eddie Bauer
Remmy, thanks very much for the response. I have not tried disconnecting the IAC valve since when I disconnected the Throttle Position Sensor it appeared to correct the problem. Do you think the I should replace the IAC?

All vacuum lines are connected, I have smoked the induction system and there are no vacuum leaks. I have not tried disconnecting the battery since replacing the Throttle Body Sensor, I will most definitely do this. I assume I have to disconnect the negative terminal and leave it for a few minutes before reconnecting?
 






Dancing Bear

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April 14, 2008
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City, State
Annapolis, MD
Year, Model & Trim Level
1991 Explorer Eddie Bauer
Remmy, per your suggestion, I disconnected the battery since I replaced the TPS, and so far the problem appears to be resolved. It has been almost a week now, and it has been idling fine with no problems for that time. Thanks very much for your suggestion and response.
 






Joined
January 8, 2009
Messages
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City, State
CA
Year, Model & Trim Level
95 XLT
Just had this; the shop replaced idle control valve; fixed it.
 






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