Gotta (high) idle problem

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Dec 16, 2011 | 05:47 PM

sibernut

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Gotta (high) idle problem

94 F150/302FI 2wd, A/C. engine idles high intermittently, anywhere from 1000 to 2000 while driving, almost like on "cruise". Feels like stuck throttle, real fun in traffic. Replaced TPS & throttle cable. Opened up intake, cleaned bores and throttle plates. Disconnected cruise cable. When I'm driving & it does it, if I put it in N while still moving it stays sped up for a second then drops to normal idle (750-800RPM).
Won't do it sitting still. Does it have a VSS somewhere that's FUBAR?
Any help appreciated!!

Dec 17, 2011 | 06:07 AM

Freightrain

Lead Driver

Joined: Jan 2003

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From: Ohio

Idle air motor sticking? They get gummed up. Pull it off, clean it up with brake clean and see what it does.

They usually fail and make it not idle, but who knows?

Dec 17, 2011 | 07:48 AM

Tote-M-Pole

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Joined: Nov 2010

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From: Rust/Salt Belt in SW Mich

Siber,

It does sound like the IAC. With that said have you checked for codes? Couple of thoughts
Unhook the throttle cable and manually actuate the throttle, it should feel smooth. Now do the same for the cable, it should also feel smooth.

Just my 2 cents

Dec 17, 2011 | 08:40 AM

fonefiddy

Cargo Master

Joined: Nov 2003

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From: Duluth, Mn.

It sounds like a vacuum leak.

Dec 17, 2011 | 08:49 AM

sibernut

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High idle

Tks, guys for the fast response! Yes, I have manipulated the butterflies with the cable off, even added a second spring temporarily to the linkage before the new cable. No different.
What is "IAC" ? I'll check out the vac leak thing ASAP. BTW, I have the A/C unplugged, so the compressor won't kick in & run it up. I am at the point that I'm ready to stand in front with M/W on the brake in D just to see what I can find. (I have no big life ins policy, no motive.......)

Dec 17, 2011 | 09:38 AM

ryan f150 4x4

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Joined: Jun 2006

Posts: 263

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From: peterborough ontario

the iac is in the side or top of the throttal body its easy to test start the truck and unplug it it the tuck quites the iac is work if it says running it needs cleaning or replaced

Dec 17, 2011 | 11:28 AM

sibernut

Thread Starter

Cross-Country

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IAC

I think what you are calling the IAC I would call the "mass air sensor", right ? I'll try it today, w the vac leak theory. TKS!

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Dec 17, 2011 | 02:05 PM

sibernut

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MAF

OK, unplugged it, RPM dropped a hundred but didn't quit. Is there a proceedure for cleaning other than a blow out? New looks like $76, rather try a cleaning 1st.

Dec 17, 2011 | 08:02 PM

#10

Freightrain

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Joined: Jan 2003

Posts: 9,893

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From: Ohio

Unbolt it from intake, get yourself a can of brake clean(not carb cleaner) and spray it liberally in the two holes. Using a small scewdriver you should be able to move the rod back and forth. Look inside and you'll see the "valve" seat area. Make sure it's not carboned up. You can remove the soleniod portion and work on the valve itself.

How it works: it's a controlled vacuum leak as it allows more air pasted the throttle blades. If it sticks open/closed or gummy it will make it idle fast or slow depending on condition.

Usually cleaning them up will make a drastic change in idle quality.

Dec 20, 2011 | 06:10 PM

#11

sibernut

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Cross-Country

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Cleaned MAF sensor, replaced IAC. Still doing it, but better. Only idles up at 1500 now in gear, stopped. Keep the ideas coming, I appreciate the help!