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Old 08-04-2012, 01:30 PM   #1
Strat1
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Idle surges at low rpm.

My buddy has a 1984 and trouble with low rpm running / (O2 Sensor?), he'll be going along about 35 mph @ 1200 rpm and for no reason he can figure it will surge up to about 1400 rpm them fall back to 1200, this is with no extra loads (ac etc).

He's had a couple mechanics look it over and change the sensor out, it will run great for a day or few hours then revert back to the 'surging' .


Any obvious solutions ?

Thanks!!
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Old 08-05-2012, 04:01 AM   #2
WNH
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I had a similar problem with my '88. After changing a bunch of parts [IAC etc], I bought a remanufactured ECM, and it never happened again.

I'm not saying this is your car's problem, but that's what worked for mine.
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Old 08-05-2012, 10:28 AM   #3
wildcatlock
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Quote:
Originally Posted by Strat1 View Post
My buddy has a 1984 and trouble with low rpm running / (O2 Sensor?), he'll be going along about 35 mph @ 1200 rpm and for no reason he can figure it will surge up to about 1400 rpm them fall back to 1200, this is with no extra loads (ac etc).

He's had a couple mechanics look it over and change the sensor out, it will run great for a day or few hours then revert back to the 'surging' .


Any obvious solutions ?

Thanks!!
look for vacum leaks especially around the throttle blade shafts. They will allow unknown air to enter and the computer tries to comensate with the IAC uintil it cant adjust anymore. If it also has a "surge" at idle in gear ( if auto trans) or at free idle ( man trans ) then check this carefully, you would be amazed what unknown ( to the ECM ) air will do to the way it runs at part throttle and below yet not really effect full throttle performance.
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Old 08-09-2012, 02:06 AM   #4
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Vacuum leak.

Detection process follow to a 'T':

EVERYone should bookmark this post too.

Quote:
Originally Posted by Blade_1 View Post
Idle to warm motor. MUST BE CLOSED LOOP WARM.

Brick on GAS pedal, block TB linkage, anything to get a STEADY idle - about 2k rpms. MUST BE STEADY.

Spray starting fluid everywhere air can get sucked in, A LITTLE AT A TIME, until the motor surges. That's the leak. If it's in a tight spot, light a book of matches, blow them out quickly, and feed the smoke to the draw. Don't stop when you find one leak either. Plenum-to-runners, runners-to-intake, emissions hoses (EVAP cannister, EGR) valve covers, brake booster, EVERYWHERE. Vacuum/intake leak will make a 2012 car lope idle, and also will make a 50 year old lawnmower lope idle.

Bookmark this page!!!
This ain't hard. But I know of only 1 PERSON who ever got it right, and found his intake leak.

Even mechanics don't know how to get it right...
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I'm always thinkin' (you can tell by the smoke). And we all know stuff don't work when the magic smoke gets out.

Never got paid for wrenchin' so I know nothin' ( I can guess pretty good tho' )...

NO ONE can SMOKE the tires at 60mph. PERIOD.
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