1997 Ford Explorer engine rev

Tiny
JUSTINF89
  • MEMBER
  • 1997 FORD EXPLORER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 94,500 MILES
Every four or five seconds, my 4L sohc will rev up about 100-150 rpms, whether im at idle in park or driving at speed. Its less noticable at speed but if you listen for it it can be noticed and there is a slight jerk. At idle, the small rev will actually overpower the brakes if they aren't pushed hard enough. This 100rpm jump only lasts about a second. Any thoughts? It happens all the time. Thanks.
Monday, April 5th, 2010 AT 4:45 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi:
My first guess is either a bad throttle position sensor (TPS) or idle air control valve (IAC). However, that is a guess. Has the check engine light ever come on?

Let me know.

Joe
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Monday, April 5th, 2010 AT 9:38 PM
Tiny
JUSTINF89
  • MEMBER
  • 22 POSTS
The engine light has not come on since we've owned it for the last 1500 miles. Can these components be checked with a miltimeter? Thanks.
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Monday, April 5th, 2010 AT 9:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Yes they can. If you need directions, let me know. Before you do it, however, just for the heck of it, take the car to a nationally recognized parts store and ask them to scan the computer. Since you only put 1500 miles on it, there could be a code stored that will identify where the problem is coming from. It will save you the headach and most parts stores will do it for free, so there is no money out of pocket for you.

Let me know what you decide. It's midnight here and I have to get up at 5AM for work, so I'll look for your reply tomorrow. Have a good evening.

Joe
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Monday, April 5th, 2010 AT 10:46 PM
Tiny
JUSTINF89
  • MEMBER
  • 22 POSTS
I appreciate the help. I took it up to advance auto and there is no stored codes. Oddly enough, when I changed out my ac clutch cycle switch, now it runs perfect. Obviously this doesn't make sense but it has done this idle problem for 1500 miles and now it stops? Would you happen to know the correct resistance values I should have when checking the two components? I would like to check them just in case. Thanks for all your help.
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Tuesday, April 6th, 2010 AT 2:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Actually, it does make sense. The AC cycle switch sends a signal to the PCM (Computer) telling it when the compressor is being used. As a result, the PCM compensates for the added load on the engine by raising the idle so the engine doesn't die. If the switch was sending inaccurate information to the PCM, it could have been causing the RPM's to change.

I think you found the problem, but if you still decide to check the other things and need me to look it up, let me know. I'll be glad to help.

Joe
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Tuesday, April 6th, 2010 AT 10:28 PM

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