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Throttle hang with defroster on.

P

pre98zetec

Veteran CEG'er
Joined
Sep 3, 2004
Messages
782
Location
Kennedy, New York
Been having this problem for the past month, didn't bother at first (because I didn't use the defroster alot).. Now, using it more and more its begining to annoy me.

I searched on the old CEG and couldn't find anything. the rpms hang when i take my foot off the gas (to a point where the car will keep the same speed on flat ground.. like the cruise control was on). WHen you go to stop the car 'pushes' back, and if you slap it into nuetral it will hang at 2000rpm and if you blip the throttle it will stay at asteady 3100 and eventually come down. If you turn the defroster off it immediately goes back to normal (750rpm nuetral 500rpm drive).

I've been checking for leaking vacuum lines, no go.. I can't find any that are off but I will keep looking.

car is a 96 atx zetec, ac is completely removed (pump is off, lines are still there) but I don't think it matters.
 
Clean the throttle body and clean/change the IAC valve.

IAC cleaning
Zetec IAC location.

For the Zetec I-4, you need to access the IAC from the bottom of the car.

IAC cleaning
from Ray's UIM/LIM how to in Duratec Maintenance how to.

"Replacing the IAC gasket:
(From IAC faq)
Over time, the IAC (Idle Air Control) valve becomes sticky due to buildup from the EGR and PCV systems. It can stick partially open such that idle quality is adversely affected, and engine RPM's will not drop below 1500. For a while, blipping the throttle will restore normal idle, but this only works for so long.

The fix is to remove the IAC valve by unbolting the two 8mm bolts that hold it on and disconnected the wiring plug. If you are careful enough, replacement of the gasket will not be necessary. The gasket costs less than US $1.00, so it is no tragedy if you destroy it. Once the valve is off, spray it out with some carb/intake cleaner and make sure any gunky residue is gone. Reattach, and you are done. It is a lot cheaper than a new IAC, which runs around US $70. Note: Ford claims the IAC cannot be cleaned, but this is not true in my experience." Ray.

Location of the IAC for the Zetec.

"It's on the back side of the intake plenum under the throttle body area." DESIGN.

I looked at the Haynes manual and the Zetec IAC valve is located next to the starter. Below are the steps from the 1996 Ford CD to remove it .

Idle Air Control (IAC) Valve


Removal

1. Disconnect battery ground cable

2. Remove the air cleaner outlet tube and resonator assembly.
3. Disconnect the main chassis vacuum line.

4. Disconnect the ignition coil and radio interference capacitor wiring.

5. Remove the fuel line bracket retaining bolt.

6. On 2.0L engine equipped vehicles, raise vehicle on hoist.
7.
7. Disconnect the engine control sensor wiring or fuel charging wiring (depending upon application) from the idle air control valve (IAC valve) at the idle air control valve connector.

8. On 2.5L engine equipped vehicles, remove retainer for engine control sensor wiring from the upper retaining stud bolt.

9. Remove the two idle air control valve retaining bolts or stud bolt (depending upon application).

10. Remove the idle air control valve and idle air control valve gasket.

Installation

1. Note: If scraping is necessary, be careful not to damage idle air control valve or intake manifold idle air control valve gasket surfaces or drop material into intake manifold.

Clean idle air control valve gasket mating surfaces.

2. To install idle air control valve, reverse Removal procedure. Tighten the fuel line bracket bolt to 8-12 N-m (71-106 lb-in).

3. On 2.5L engine equipped vehicles, tighten the retaining bolt and stud bolt to 8-12

4. On 2.0L engine equipped vehicles, tighten the idle air control valve retaining bolts to 8-11 N-m (71-97 lb-in).

TB cleaning.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=trouble&Number=920243&Forum=trouble&Words=p0401&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=919728&Search=true#Post920243

IACzetec tbcleaning throttlebodycleaning
 
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I have the exact same problem. I've done a compete TB and IAC cleaning but still have same problem. With defroster off it runs perfect.
 
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I have same problem here, this happened after TH Fix....i'll try changing IAC and cleaning TB. If that doesn't solve problem i'll make a bigger hole in cooper cap of TH Fix.
 
I was going through a bunch of threads looking for some info on a different topic and ran across this one. Figured I'd mention that AFAIK the PCM controls the opening of the IAC Valve and therefore the throttle hang when the A/C compressor is activated. In other words, the PCM is telling the IAC Valve to open excessively or too quickly when the compressor cycles on.

The pipe cap "TH fix" is very effective at eliminating both TH with A/C off and the "moose" sound. But only a PCM reflash can completely address the "TH with A/C on." And I don't think Ford ever came out with a reflash that completely fixed this issue. I've lived with it ever since I've had my car.

If anyone else has had different experience, I'd love to hear it.
 
Wow, this happened to me last night, the damn rpm's got stuck @ 4K and wouldnt come down. Next time it happens Ill turn off the defroster. I almost got into an accident because I passed somone on a bridge and the throttle hung wide open. I push in the clutch and it hit the rev limiter and stopped.. scary stuff..
 
My cars rev sticks like that when the cruise control is on. check your throttle cable to make sure there's no bindings and cruise control actuator for the same. When it happened to me I was going on I 80 west right before SLC through the canyon (lots of turns lots of crap in my pants.)
 
Tony2005 said:
Did you try the 97 moose fix? (new IAC valve with 45 degree hose)
Click to expand...

Yep, in fact that was the first mod I ever did to my car. I still have the old bagpipe assembly :lol: . My PCM has also been reflashed once or twice over the years on those rare occasions when it's been brought to the dealership.
 
Disconnect the plug for the A/C that is in the pipe right in front of the coolant tank. Mine went bad and was causing the TH with defrost on problem. I'll fix it is the spring.
 
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