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Hello, I've done a search but couldn't really come up with an answer.
My car bucks while decelerating only. This happens in any gear, at any speed.
Otherwise, acceleration and cruising are smooth.
No CEL.
Any ideas?
Tune-up is completed except pcv valve.
Car is a '98 zetec MTX.
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Have tried checking/cleaning/changing the IAC valve?
Edit.Scan it at Advance or Autozone. You may have an intermittent code which will not turn on the CEL yet. In the meantime, check your air filter and change your fuel filter. If the stumbling is during idling (rather than high rpms), it could be the IAC valve (usually no CEL codes with this). Also clean the MAF cleaner.
Originally posted by Tony2005:
Change fuel filter, air filter, clean IAC, clean MAF, clean throttle body and put HEET or gas stablilizer in gas tank. All cheap maintenance items.
Fuel filter.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=v6maint&Number=958655&page=0&view=collapsed&sb=5&o=186&fpart=1
MAF
http://www.contour.org/mods/mods.php?s=howto&displayid=36
and
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=zetecmaint&Number=989728&page=&view=&sb=5&o=&fpart=1&vc=1
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
Last edited by Tony2005; 07/15/06 07:04 PM.
"Always do the cheap and easy ones first."
1996 V6 ATX 96K miles
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Thanks!
The MAF was just cleaned, and the fuel filter changed at the same time.
Haven't touched the IAC, but it stumbles at any rpm speed, but only while decelerating.
The car idles ok.
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What about air filter? And get the codes read and post the codes. Free service at (I think) Mister Transmission.
Originally posted by Tony2005:
Locations for Mister Transmission. Call to confirm the free CEL code check.
http://www.mistertransmission.com/dealer_locations/dealer_locations.asp
WalMart, KMart, Target, Sears, auto specialty stores, some auto repair shops sell the Code Scanners for $50 and up.
Last edited by Tony2005; 07/15/06 07:12 PM.
"Always do the cheap and easy ones first."
1996 V6 ATX 96K miles
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Yes, the air filter was changed.
I reset the computer to clear any codes, but that was to ill-effect.
I'll get the car scanned one day when the garages are open.
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If you reset the computer, the codes are erased. Need to drive it a few days (or when the CEL comes on) before going to Mister Transmission.
"Always do the cheap and easy ones first."
1996 V6 ATX 96K miles
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After driving the car several days/ hundreds of miles, I had the computer scanned.
There are no codes, but the sensor is not getting a reading from the 4 following sensors...
1)O2S (Both 02 sensors plugged in and connections good, no frayed or cut wires)
2)CAT (If this is the catalytic converter, I had no idea it had a sensor other than the o2's)
3)HTR (I'm assuming is the heater, but is working fine)
4)EVAP
So here are my following questions...
1) If there's a bad o2 sensor, wouldn't it set a code instead of the sensor not being picked up?
2) Could the bucking under deceleration be a symptom of a clogged catalytic converter, if not what are the symptoms of one?
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Originally posted by 337:
After driving the car several days/ hundreds of miles, I had the computer scanned.
There are no codes, but the sensor is not getting a reading from the 4 following sensors...
1)O2S (Both 02 sensors plugged in and connections good, no frayed or cut wires)
2)CAT (If this is the catalytic converter, I had no idea it had a sensor other than the o2's)
3)HTR (I'm assuming is the heater, but is working fine)
4)EVAP
So here are my following questions...
1) If there's a bad o2 sensor, wouldn't it set a code instead of the sensor not being picked up?
2) Could the bucking under deceleration be a symptom of a clogged catalytic converter, if not what are the symptoms of one?
Answer yes to both your questions. If the converter is clogged, chances are you will also get a P0420 code. You may want to do the el cheapo plugged exhaust test for the Zetec. Unplug upper O2 sensor. If performance improves, then it is probably a plugged exhaust.
Your 4 non readings are either due to the OBD II cycle not completed or some the monitors not being applicable to the Contour. I will check tomorrow after driving my car and post.
"Always do the cheap and easy ones first."
1996 V6 ATX 96K miles
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Thanks, I appreciate it!
When you say to unplug the upper o2 sensor, do you mean to disconnect the connector, or to remove the sensor completely?
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1) Disconnect negative terminal battery (note you will lose all CEL codes stored in the PCM memory)
2) Disconnect Upper O2 sensor connector
3) Remove Upper O2 sensor (use 7/8 inch or 22 mm crescent wrench or O2 sensor removal tool).
What you are doing is give the exhaust an outlet. If car performs better, you probably have a plugged catalytic converter.
"Always do the cheap and easy ones first."
1996 V6 ATX 96K miles
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