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Old 11-30-2012, 04:37 PM   #1
Sonic26
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IAC Fail after ECU reset?

Hello everyone, I'm hoping somebody could help me out with an issue regarding idle power.

The other day I attempted to reset my car's ECU by disconnecting the negative terminal of the battery for 15-20 minutes and then leave her running idle for another 15-20.

I done this because I was having some really erratic idle problems (when cold) and acceleration problems too that annoyed the hell out of me and a lot of suggestions on the web was to reset the ECU. I have done this before with positive results but this time I wish I hadn't have done it.

While the hood was open I thought I'd take the opportunity to unplug the MAF Sensor to see if the connections were clean as was also suggested online. Everything looked good so I plugged it back in and went ahead with the reset.

So afterwards, I hop in the car and take her for a ride to see if there is an improvement in rough idle and acceleration. All seemed good until I was stopping at traffic lights when a new symptom appeared that I never encountered before. As I was slowing to come to a complete stop the revs would drop all the way and eventually the engine would cut out. This has been happening ever since. Now what I have to do is carefully apply some pressure on the accelerator (with clutch engaged) to keep her "awake" while alternating to the brake pedal to come to a stop.

These symptoms seem to be IAC related, but I didn't do anything else when the hood was open except disconnect the battery and check the MAF Sensor connection.

Does anyone know what I done wrong that would cause the IAC to be acting up?

Thank you in advance.



BTW, I'm a rookie, so go easy on me. :)


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Old 11-30-2012, 09:39 PM   #2
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Quote:
Originally Posted by Sonic26 View Post
I done this because I was having some really erratic idle problems (when cold) and acceleration problems too...Does anyone know what I done wrong that would cause the IAC to be acting up?
hi and welcome to the forum.

Has your IAC ever been cleaned or replaced? If not, then your suspicions might be correct...but, you're driving a 12 year old Focus, so it could be one or more things on a long list of faults, many of which won't trigger a check-engine light nor a code.

Aside from stalling, did the car drive exactly the same before & after the ECU reset?

Provide some more info on the car's repair history and its other symptoms. Since you said "I have done this before with positive results", it sounds like you've had an underlying problem lurking for some time, and it was only a matter of time before it became a full-fledged failure.
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Old 11-30-2012, 09:55 PM   #3
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Old 12-01-2012, 02:36 PM   #4
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Hi. Thank you for the welcome.

I only own the car a year and I'm not sure what was done to it before by previous owners except air filter change, oil filter change and timing belt change. That's the only thing written in the service log.
Since I owned it, all that has been done was head gasket leak repair, oil change, oil filter change, and a new breather hose fitted (around 6 months ago). I checked the air filter and it is spotless.
The guy that done the work for me said that my throttle position sensor might not be collaborated properly but told me it's nothing to worry about.

I bought a fuel filter which I plan on getting fitted soon. I thought it would do no harm to have a fresh fuel filter change since I don't know how long the current one has been there.

Reasons for ECU reset :
Crazy idle when starting cold. The revs start off normal, then within 20 seconds after starting they bounce up and down (from around 1000 to 3000 and back down in little under a second). It only takes about two minutes of driving to come back to normal and will remain normal for the rest of the day.

Hesitant acceleration. It feels like some of the power that should be delivered to the engine is getting bypassed somewhere. This is most noticeable in 1st and 2nd gear. When accelerating the revs will go above 3000 but the car will be moving very very slow so then I change into 2nd but the car has to pick up the speed loss from where I left off in 1st and so on. This happens all the time regardless of weather conditions.

High pitched hiss. This only happens at morning. May be weather related because I don't think I've noticed it on a dry warm morning. When driving with a cold engine (only morning) I can hear a hiss coming from somewhere under the hood when clutch is engaged and changing gears. It also seems that the revs take longer than they should to drop (regardless of time of day and weather) as if I partially have my foot on the accelerator (I don't).
Keep in mind that this was before the problem that I have now. (Hesitant acceleration and high pitched hiss still remain)


The car was driving the same after the ECU reset minus the rough idle when starting cold which I'm sure will return in time as did the last time I done the reset.

Don't know if this helps diagnosing the problem but, I have noticed when the engine is ready to die the battery light will illuminate and then extinguish when I get the revs back up.
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Old 12-01-2012, 02:53 PM   #5
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I'll take a stab at the easy part:

Quote:
Originally Posted by Sonic26 View Post
When accelerating the revs will go above 3000 but the car will moving very very slow...When driving with a cold engine (only morning) I can hear a hiss coming from somewhere under the hood when clutch is engaged and changing gears.
sounds like a classic case of a worn-out clutch: the first part is clutch slippage and the second part might be a bad throw-out bearing; both would be replaced in the same job.
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Old 12-01-2012, 03:13 PM   #6
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Hi Beautious, thanks again for the reply.

I have had the clutch tested by 3 different mechanics and they all said my clutch was fine.
Is this in reference to the engine stalling when coming to a stop too?
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Old 12-01-2012, 03:25 PM   #7
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Also, I forgot to mention in my other post that I sometimes hear a fluttering sound coming from under the hood near to the ground when accelerating. My main concern at the moment though is the stalling when stopping issue. I could live with the other issues but with this I have to change my style of driving when slowing down and it's kinda dangerous if I'm taking a corner and suddenly my power shuts off.

Thank you for your inputs so far.
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Old 12-01-2012, 04:05 PM   #8
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Quote:
Originally Posted by Sonic26 View Post
I have had the clutch tested by 3 different mechanics and they all said my clutch was fine.
then I'm out of ideas on your Hesitant acceleration issue. On a 12 year old car that revs to 3000 rpm and doesn't go anywhere under acceleration, the easy diagnosis is a worn clutch disk.


Quote:
Is this in reference to the engine stalling when coming to a stop too?
do you shift the transmission into 1st gear or neutral at a stop? If you keep it in gear with the clutch pedal depressed, then the engine would bog down if (for some reason) the clutch was not being fully disengaged. But, if that was the case, then it would also be hard to shift during normal driving.

So, back to your primary concern: assuming you did not damage the MAF sensor, then your resetting the ECU did not create a new problem. Like I said in my original reply, your Focus has some old, underlying problem(s) that is now getting worse. Since you already have a fuel filter on hand, replace that for starters. If your Hesitant acceleration issue is in fact the engine being starved of fuel (which might feel like it's losing power under load) then a clogged fuel filter might very well be responsible for that.

I understand your impatience & frustration with all of the unknowns here, but when diagnosing an old car with an unknown service history and a laundry list of likely faults, then the best strategy is to analyze one thing at a time, rather than scattershot. Your instinct about the fresh fuel filter is correct; replace that and then move on to the other symptoms.
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Old 12-01-2012, 05:20 PM   #9
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Quote:
Originally Posted by my_beautious_ZX3 View Post
then I'm out of ideas on your Hesitant acceleration issue. On a 12 year old car that revs to 3000 rpm and doesn't go anywhere under acceleration, the easy diagnosis is a worn clutch disk.
Yeah, I was kinda happy that so many people suggested the clutch (even though very pricey) that I may have a resolution, but turned out not to be, ah well.


Quote:
Originally Posted by my_beautious_ZX3 View Post
do you shift the transmission into 1st gear or neutral at a stop?
Depends on how long I know I'll be waiting at the lights. If I know I'll be there a while I shift into neutral, otherwise I shift into 1st to be ready.


Quote:
Originally Posted by my_beautious_ZX3 View Post
assuming you did not damage the MAF sensor, then your resetting the ECU did not create a new problem.
That's relieving to know, thank you.

I will install the new fuel filter when I get some free time from work.


I really appreciate your input beautious, thank you.




Just wondering if anyone else out there had similar issues and want to add something? I'd really appreciate it, thanks.
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