low speed surge
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Postmaster
Joined: Sep 2004
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From: wi
low speed surge
ive noticed and realy dont know how long my 92 has been doin this but when ya go threw town about 25-30 mph the little 302 surges a little the rpm will go up and down enuff to hear but not enuff to make the speedo jump around. it dont do it at hi-way speeds that i can tell but then again i cant hear that great so it might be. any ideas what could cause this condition? the engine only has around 25-30,000 miles on it installed by ford a couple years ago. im thinking the tps might be on its way out but i might be wrong. the check engine light isnt on either
Elder User
Joined: Apr 2007
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From: Los Alamos
Does it idle smooth at a stop?
At "idle" speeds, the Throttle Air Bypass controls idle. If your computer thinks you over 225* (coolant temp sensor reading high), or you are over 225*, it will raise your idle 100 to 200 rpm. Could also be your HEGO searching, or getting lazy.
Or could be a vacuum leak, and thinking about it, I would start looking for that first.
At "idle" speeds, the Throttle Air Bypass controls idle. If your computer thinks you over 225* (coolant temp sensor reading high), or you are over 225*, it will raise your idle 100 to 200 rpm. Could also be your HEGO searching, or getting lazy.
Or could be a vacuum leak, and thinking about it, I would start looking for that first.
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Postmaster
Joined: Sep 2004
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From: wi
it idles fine cold or warm some times if i shift in gear before the high idle come down itll act silly. whats a HEGO? i checked for a vacum leak before askin here and alls good there even did the either test
Elder User
Joined: Apr 2007
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From: Los Alamos
If it acts up when it's still on high idle, I would suspect the Throttle Air Bypass may be not working right/opening all the way.
MAP sensors can make them act somewhat like that, too. Check the MAP vacuum line for oil in the line, as I have seen them get oil buildup in the line and ruin the MAP.
MAP sensors can make them act somewhat like that, too. Check the MAP vacuum line for oil in the line, as I have seen them get oil buildup in the line and ruin the MAP.
New User
Joined: Feb 2008
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I had this problem 2 weeks ago.
I had read many posts on this forum about the problem, and was easily able to find and fix.
The IAC was the problem.
I would notice at low speeds when I let off the accelerator the motor would continue at the same rate for about 3-5 seconds and then come down.
Then when it was sitting idle I started to notice that it would go up and down.
I would try this.
I cleaned it as this forum suggests, however, it only lasted a day and ran good, the next day it was back to the same onld thing, and I replaced it.
I haven't had a problem since.
Just my $.02 worth.
I had read many posts on this forum about the problem, and was easily able to find and fix.
The IAC was the problem.
I would notice at low speeds when I let off the accelerator the motor would continue at the same rate for about 3-5 seconds and then come down.
Then when it was sitting idle I started to notice that it would go up and down.
I would try this.
I cleaned it as this forum suggests, however, it only lasted a day and ran good, the next day it was back to the same onld thing, and I replaced it.
I haven't had a problem since.
Just my $.02 worth.
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