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Discussion Starter #1 (Edited)
I have read through a lot of threads about egr, iacv, vac/ exh leak, etc., but my problem isn't 'exactly' the same as others.

My car seems to idle perfect, anytime it is idling, and LTFT and STFT stay at 0 at idle.

My issue is that the engine dies everytime I let it drop to idle on its own.

I can keep it from dieing if I stay in gear all the way down to idle speed before I push the clutch.

Everytime it dies while I'm still rolling, I can let go of the clutch while still in 5th or 4th and it gently restarts and idles seemingly perfect as I continue to come to a stop, as long as I'm going very slow.

If I clutch-restart the car while still above 30-40 mph, the car will idle 'seemingly' perfect for a few seconds, then just die.
I can repeat it still rolling over and over again.
Everyone else with this issue complained of poor idle when idling, but my idle seems smooth and as though all is well when idling.

If I start the car, it will idle smooth all day so long as you don't rev it up and let it drop on it's own.

Once stopped and still running, it will idle the whole time like nothing is wrong.

Other clues are:
-My LTFT hovers erratically from +7 to +10 and STFT at -3 to +4 when I'm at part throttle, crusing 55 in 4th gear

-Car does not have idle problem until warmed up.

-All vacuum hoses are new, in place, and look good all over.

-I already checked for exhaust leaks and only found two by the muffler. Fixed them, no change. No other exhaust leak found. I checked the manifold, all over every pipe, junction, everywhere, no leak. Test was done with a powerful blower sealed to the tail pipe. (Worked very well btw! )

-When crusing or wot, exhaust smells of nox fumes. Other cars don't like riding behind me because of it.

-Fuel filter changed for maintenance. No change. Air filter and pcv are still new.

-MAF seems to read perfect and is responsive to all throttle changes on Torque app's graph.

- There is no smoke from exhaust, no power loss, no hiccupping at all. In fact, it runs amazing.

It just won't grab and hold idle on its own.

Sorry for the long read.
Thanks for any ideas.

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What year?
What engine?
How many miles?
How long has been problem?
DTCs?
How long since last ignition service (plugs/wires/coil)?
How long since O2 sensors replaced.
How long since TB/MAF cleaned?

ST/LTFTs < +/-10 = normal

Doesnt like closed loop

Have you looked at live data to see that the O2 sensors are cycling normally in closed loop?
Verification of VSS signal to PCM?

This seems key:

My issue is that the engine dies everytime I let it drop to idle on its own.

I can keep it from dieing if I stay in gear all the way down to idle speed before I push the clutch.

Everytime it dies while I'm still rolling, I can let go of the clutch while still in 5th or 4th and it gently restarts and idles seemingly perfect as I continue to come to a stop, as long as I'm going very slow.

If I clutch-restart the car while still above 30-40 mph, the car will idle 'seemingly' perfect for a few seconds, then just die.
I can repeat it still rolling over and over again.
Based on that I would suspect a possible signaling/continuity issue between the CPPS and the PCM. Have you verified the circuit?

Paul
 

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Discussion Starter #3
What year?
What engine?
How many miles?
How long has been problem?
DTCs?
How long since last ignition service (plugs/wires/coil)?
How long since O2 sensors replaced.
How long since TB/MAF cleaned?

ST/LTFTs < +/-10 = normal

Doesnt like closed loop

Have you looked at live data to see that the O2 sensors are cycling normally in closed loop?

Paul
Sorry.
I should have included all that.

01 zetec zx3
120k
Problem has been a couple of weeks now.
No codes.
Wires, coil, and plugs have ~10k and look great.
Valve cover is good and under 10k since replaced.
Pcv, air filer, vacuum lines, ff, pcv hoses all new.



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Discussion Starter #4
TB is clean.

MAF seems to read correctly according to the Torque app, but, hasn't been cleaned.
I'll do that tonight.

Upstream was replaced a year ago, and has always shown a weird trace, rather than a smooth sine wave. It has always looked weird on a graph in real time (I'll post pics).

Downstream is original and has been dead for 12 years with no real issue.

TPS reports responsively on the app.

Fuel pressure stays perfect.




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If high mileage may be from that alone. Engine drops down fast enough to then drag it down to die as an older engine does not make enough torque to stop it from dropping to zero. It can stabilize with a second to adjust like you show (standing idle all day long) but not having that and engine in freefall the inertia takes it right past that point.

Check all normal idle air to engine like PCV positively not blocked in any way and need clean TB butterfly and bore right where they touch and IAC. Past that on one of mine I had to once all that was guaranteed open the TB butterfly up a very small amount to let more air in than normal. Older engines need slightly more air due to dragging down in normal idle, again, they have lost a lot of idle rollover torque. What ring and valve seal do when they flee due to engine wear. A compression test may show something there too.

That adjustment is touchy, you can easily get out of IAC range and then PCM sends you the typical rpm too high thing or the idle begins to hang high. There IS a small amount of adjustment room there though, I went between 1/8-1/4 turn more open on the butterfly setscrew and worlds of difference doing it. Mine mainly died when a/c went on at idle. Freshly charged so it had a lot of drag. If ATX car then watch your engine braking at throttle dropped off on decel, the braking is greatly influenced by the butterfly setting and it will likely change a bit to be less. Which helps your issue too, rpm drops at a slower rate.

Mine which used to die all the time hasn't done it in forever. Of course other things like ignition need to be in line too, watch the plug wires, they go bad very easy at pulling them to work on plugs.

The issue is that the IAC tries to respond but they do not like lightning, it takes a fractional second to move, you don't have that at engine freefall. Another thing.....if you never change the butterfly to be open more on an older engine the IAC simply opens more itself but again, that takes time. If you artificially bump the butterfly open then the IAC no longer has to OPEN, rather it will look to CLOSE meaning you already have enough idle air to keep it running hopefully. You didn't have to wait for a response from IAC as you already had the air amount built in.
 

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Consider too a vacuum leak showing up at the much higher vacuum of decel ONLY.

I mention it because the zetec has a crap super thin gasket section at the idle bypass port at the joint between TB and intake.

I've had that thin section pull out sideways to then reseat back in place before and it gave me fits finding it. The entire TB does not sit right on the intake surface flat, rather the bolt holes in the corners have slight 'stands' molded into them to hold up the TB assembly roughly .010" or so high on the intake. That airspace is what allows the gasket to pull out of place, it is not hard pinched to not move at all. The gasket as well with age loses a whopping amount of the physical 'body' stiffness the material has normally that would stop that, it becomes extremely flexible. I could see by the coloration of the silicone there that the gasket right there had been sucked out in the wind at least part of the time, it was twisting sideways out of place. Kooky, man.

My problems there were not the same as here but with a little imagination I could see the gasket moving at decel only to leak to help kill engine then falling back into normal place to run right. Far-fetched but not impossible.
 

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Discussion Starter #8
If high mileage may be from that alone. Engine drops down fast enough to then drag it down to die as an older engine does not make enough torque to stop it from dropping to zero. It can stabilize with a second to adjust like you show (standing idle all day long) but not having that and engine in freefall the inertia takes it right past that point.

Check all normal idle air to engine like PCV positively not blocked in any way and need clean TB butterfly and bore right where they touch and IAC. Past that on one of mine I had to once all that was guaranteed open the TB butterfly up a very small amount to let more air in than normal. Older engines need slightly more air due to dragging down in normal idle, again, they have lost a lot of idle rollover torque. What ring and valve seal do when they flee due to engine wear. A compression test may show something there too.

That adjustment is touchy, you can easily get out of IAC range and then PCM sends you the typical rpm too high thing or the idle begins to hang high. There IS a small amount of adjustment room there though, I went between 1/8-1/4 turn more open on the butterfly setscrew and worlds of difference doing it. Mine mainly died when a/c went on at idle. Freshly charged so it had a lot of drag. If ATX car then watch your engine braking at throttle dropped off on decel, the braking is greatly influenced by the butterfly setting and it will likely change a bit to be less. Which helps your issue too, rpm drops at a slower rate.

Mine which used to die all the time hasn't done it in forever. Of course other things like ignition need to be in line too, watch the plug wires, they go bad very easy at pulling them to work on plugs.

The issue is that the IAC tries to respond but they do not like lightning, it takes a fractional second to move, you don't have that at engine freefall. Another thing.....if you never change the butterfly to be open more on an older engine the IAC simply opens more itself but again, that takes time. If you artificially bump the butterfly open then the IAC no longer has to OPEN, rather it will look to CLOSE meaning you already have enough idle air to keep it running hopefully. You didn't have to wait for a response from IAC as you already had the air amount built in.
Thank you for those tips!

I'm going to tinker around with the car more tonight since I'm off tomorrow.

I'll give that adjustment a try all by itself, just to see what kind of difference I can get out of it.



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Discussion Starter #9
Consider too a vacuum leak showing up at the much higher vacuum of decel ONLY.

I mention it because the zetec has a crap super thin gasket section at the idle bypass port at the joint between TB and intake.

I've had that thin section pull out sideways to then reseat back in place before and it gave me fits finding it. The entire TB does not sit right on the intake surface flat, rather the bolt holes in the corners have slight 'stands' molded into them to hold up the TB assembly roughly .010" or so high on the intake. That airspace is what allows the gasket to pull out of place, it is not hard pinched to not move at all. The gasket as well with age loses a whopping amount of the physical 'body' stiffness the material has normally that would stop that, it becomes extremely flexible. I could see by the coloration of the silicone there that the gasket right there had been sucked out in the wind at least part of the time, it was twisting sideways out of place. Kooky, man.

My problems there were not the same as here but with a little imagination I could see the gasket moving at decel only to leak to help kill engine then falling back into normal place to run right. Far-fetched but not impossible.
I have had valve cover gaskets do exactly that.

Good call.
I will check that as well.

I never think about that seal because we aren't supposed to disturb it or whatever, but, I did pull the TB off of my other focus and put it back on with seemingly no issues.

A couple of ideas:

Since my car dies if trying to idle whilst rolling over 30mph, yet, is fine if I'm only going 5mph, could the MAF be wrong even though it is seemingly tracing perfectly on the graph?
Maybe it's not wrong about airflow, but, just not heating up to it's proper temp, then, sending a false intake temp to the ecu?

Another thought I had that I plan to check tonight is the timing belt could have stretched a little too much.
It's at 120k after all.

I read on here about someone who had their belt stretch just enough to retard their exhaust cam a couple of degrees and cause my dieing issue.

Thanks again for the ideas!



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Discussion Starter #10
My question about the MAF is more about my fumey exhaust issue.

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Can't say on MAF, which sometimes are so wonky they need to be changed to really know.

The exhaust timing changing only a couple of degrees won't affect spit, engine doesn't see that small an amount. That person was in error. The Contour with exhaust VCT moves the exhaust around 10 degrees all day long (retard, how the EGR gets more exhaust gas to intake to work) with no issue and the SVT moves intake even more than that I think. The question becomes one of not just 10 degrees but WHICH 10 degrees, if close to limits that will be an issue but if within a running range then really no effect at all.

Heavy exhaust smell says too rich or incomplete ignition. Low compression can do the same as ignition, you must have squeeze to burn all mixture with speed. Maybe a compression check is in order. Dying at dropping to idle is often an earmark of low compression.
 

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Just a thought, I had a similar issue on a '00 zx3 5spd

When clutched on coast down the engine would sometime idle so low and sometimes die, others it would rev up to ~3k on it's own

My issue turned out to be a dirty IAC, took some carb cleaner to it and it was good to go...
 

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cheap sleeper
Did you see my comment concerning the CPPS? I would think a functional issue with that would throw a DTC but you never know. Worth checking out.

Good luck
Paul
 

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Discussion Starter #14
Just a thought, I had a similar issue on a '00 zx3 5spd

When clutched on coast down the engine would sometime idle so low and sometimes die, others it would rev up to ~3k on it's own

My issue turned out to be a dirty IAC, took some carb cleaner to it and it was good to go...
I will probably end up doing it tomorrow.
I planned on doing it today, but, I ended up trying a bunch of other things first with no better result.



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Discussion Starter #15
cheap sleeper
Did you see my comment concerning the CPPS? I would think a functional issue with that would throw a DTC but you never know. Worth checking out.

Good luck
Paul
I'm sorry, I had somehow missed that one.
I can't recall what CPPS is.

I tried a few other things today.
Checked plugs, plug wires, coil, valve cover,
drove with MAF disconnected (ran like crap that way),
reset ecu and followed the Ford relearn idling then driving procedures,
Took mental notes of vacuum behavior,
Every sensor reaponds on the Torque app as it should.

A key thing I found was that my charging voltage on the app showed only 12.7V while running, so I metered the car while running and got a totally different reading of 14.6V at the battery.

With the car off, the battery measured 12.9 at the terminals.

This seems high to me, and, the discrepancy between the app voltage vs metering at the battery makes me wonder.

Another oddity:
I swapped in a battery from my svtf that was sitting at 12.2V metered at the terminals.

I haven't started it with yet.

The oddity is that, I fired up the voltage on the ODO in test mode, and the same battery that reads 12.2V at the terminals reads 11.6V on the ODO, so, I suspected the ECU ground, or any of the grounds, but, they are all nice and clean and solid.

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Discussion Starter #16 (Edited)
Can't say on MAF, which sometimes are so wonky they need to be changed to really know.

The exhaust timing changing only a couple of degrees won't affect spit, engine doesn't see that small an amount. That person was in error. The Contour with exhaust VCT moves the exhaust around 10 degrees all day long (retard, how the EGR gets more exhaust gas to intake to work) with no issue and the SVT moves intake even more than that I think. The question becomes one of not just 10 degrees but WHICH 10 degrees, if close to limits that will be an issue but if within a running range then really no effect at all.

Heavy exhaust smell says too rich or incomplete ignition. Low compression can do the same as ignition, you must have squeeze to burn all mixture with speed. Maybe a compression check is in order. Dying at dropping to idle is often an earmark of low compression.
Yooooo.
So, I got back at it again today.

Each of the things I did, I tested the car with that change alone, then put the car back the way it was after observing no difference in behavior.

I checked the TB and all looks good.

Wiped it all out anyway, but, it was all very clean from the last time I did it.

Checked plugs, plug wires, valve cover, wiring and connectors for a short or disconnected harness.

Drove with MAF disconnected, immediately threw a code and ran crappy.

Reset ECU, then followed Ford's idle and driving procedure.
It actually tries to catch itself at 100rpm instead of just dying after the ECU reset, but, it will try several times lobbing up and down from 100rpm to idle level and then croak, so long as I'm going over 40mph.

If I'm going under 40-45mph and push in the clutch now, it will hold, since the reset.

So, the problem is roughly 20% better, but still dies right away if I'm going over 45mph and push in the clutch.

A curious thing: My ODO voltage reads .5V lower than the battery meters at the terminals, even though all of my grounds and battery connections are clean and tight.

I unhooked them all anyway to verify how the contact points looked, and all was shiny.

I remember that my ODO voltage always reads a little lower than metering at the terminals, but, I thought I remembered it only being half of that of a difference, like, .3V at the most.

Maybe it was that much though.

My battery metered 14.6V at the terminals while running, but, at the same time, the Torque app was reporting only 12.6V while running.

That's the first time I've ever seen the app read differently that the car itself reads on the ODO.

One more thing of note: The car idles worse now after the ECU reset.

Before the reset, the idle was smooth and steady.

Now the idle has a faint misfire or sputter to it.
It is also idling a little lower than it was before reset.

Before reset it held a perfect 750.

Now it flutters around 600.
This is after I did the idling and driving procedures.



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Yooooo.
So, I got back at it again today.

Each of the things I did, I tested the car with that change alone, then put the car back the way it was after observing no difference in behavior.

I checked the TB and all looks good.

Wiped it all out anyway, but, it was all very clean from the last time I did it.

Checked plugs, plug wires, valve cover, wiring and connectors for a short or disconnected harness.

Drove with MAF disconnected, immediately threw a code and ran crappy.

Reset ECU, then followed Ford's idle and driving procedure.
It actually tries to catch itself at 100rpm instead of just dying after the ECU reset, but, it will try several times lobbing up and down from 100rpm to idle level and then croak, so long as I'm going over 40mph.

If I'm going under 40-45mph and push in the clutch now, it will hold, since the reset.

So, the problem is roughly 20% better, but still dies right away if I'm going over 45mph and push in the clutch.

A curious thing: My ODO voltage reads .5V lower than the battery meters at the terminals, even though all of my grounds and battery connections are clean and tight.

I unhooked them all anyway to verify how the contact points looked, and all was shiny.

I remember that my ODO voltage always reads a little lower than metering at the terminals, but, I thought I remembered it only being half of that of a difference, like, .3V at the most.

Maybe it was that much though.

My battery metered 14.6V at the terminals while running, but, at the same time, the Torque app was reporting only 12.6V while running.

That's the first time I've ever seen the app read differently that the car itself reads on the ODO.

One more thing of note: The car idles worse now after the ECU reset.

Before the reset, the idle was smooth and steady.

Now the idle has a faint misfire or sputter to it.
It is also idling a little lower than it was before reset.

Before reset it held a perfect 750.

Now it flutters around 600.
This is after I did the idling and driving procedures.



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having the same issue here but with a 05 duratec, car has the same exact symptoms as yours accept my focus has a u1900 code and a p0104 code. Im guessing bad pcm? car runs fine, has a slight misfire/ sputter during cold idle, once warmed up she idles just fine. mine only seems to stall when getting off of highways. as soon as i push the clutch in from going between 55-70 mph or so the rpm tach either falls like a rock straight down to zero or she drops down to about 100 and tries to bring herself back up to idle.
 

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Discussion Starter #18
having the same issue here but with a 05 duratec, car has the same exact symptoms as yours accept my focus has a u1900 code and a p0104 code. Im guessing bad pcm? car runs fine, has a slight misfire/ sputter during cold idle, once warmed up she idles just fine. mine only seems to stall when getting off of highways. as soon as i push the clutch in from going between 55-70 mph or so the rpm tach either falls like a rock straight down to zero or she drops down to about 100 and tries to bring herself back up to idle.
I have, of course, read that it could be the IAC.
Mine doesn't rev up when the A/C is activated.
Maybe we both need the dang thing.

I just didn't want to blame that, since I've never needed to change one in any of my Foci.

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Has anybody tried to bump open the TB a little bit more like I said a long time ago? That alone will modify the way the engine drops to idle at letting off the throttle.

On the fumey exhaust thing I believe somebody said the downstream O2 was dead for years, may have killed or clogged the converter.
 

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Discussion Starter #20
All I ever read is 'leave it the hell alone' suggestions.

Having the same problem with my daily and think it may be a blown fuel pressure regulator diaphragm.
Has anybody tried to bump open the TB a little bit more like I said a long time ago? That alone will modify the way the engine drops to idle at letting off the throttle.

On the fumey exhaust thing I believe somebody said the downstream O2 was dead for years, may have killed or clogged the converter.
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