Irritation - stumble on accel when cold

[brokencase]

For a while now my Scorpio has had this irritating off idle hesitation when it was cold.

Basically for the first few minutes of running if you stomped on the throttle it would stumble and hesitate.
After it warmed up a bit no issues.

No codes indicating any problem.

I had swapped in a spare ECT and spare throttle position sensor to no avail.

Figured it had to be a temperature sensitive issue. Leaves only the ACT as the possible culprit.

Ordered a Delphi ACT from RockAuto. Before I put it in I measured the resistance at ambient for the old and the new sensors.

Old Sensor 31K ohms
New Sensor 24K ohms.

I didn't think that was a big difference. But apparently it is.

Fired it up. Cold hesitation now gone.

Here we have a case where the EECIV can't actually see that the sensor is fully out of range, but it is off enough to cause the stumbling issue.

Very irritating.

[Fresh Air Inspector]

Hello Brokencase,

Interesting. The '88 Scorpio I purchased late last year for my better half has the same issue. No error codes so I assumed the IAC was the issue (wrong part was on the car). So I replaced the TPS (precautionary), and the IAC, after sorting the incorrect wiring diagram included with the TPS the issue remained. I went through the service history and found the PO replaced the ACT in 02/2015 (8K km, 5K mi), ago. So I took a long shot and tried a spare ECT - no change.

I have a spare ACT (aftermarket), that I will compare resistance values with the one in the car. May take a few days (other projects on the go), to update this thread.

The car won't be driven in the winter but I would like to sort this before the Fall arrives.

Looking forward to the feedback to this thread.

[brokencase]

Just an FYI my measurements were done at about 75F ambient.

and just to be clear on the symptoms. Rapid stomp on throttle - stumble then goes. Gentle rise on the throttle - no problem.

Issue disappears after the car warms up ever so slightly...like after 3 - 4 minutes.

[Ed Lijewski]

So, now we have, at least..., two instances of issues the EECIV should have set a code for, but didn't.

Yet you insisted in the case of SHIS that the clue to resolving it lies in a trouble code(s). Perseverancia vincit, well learned apparently.

Until you experienced a no-code diagnosis on your car, and then it seems the EECIV isn't as all-knowing as has been preached. Welcome to the club.

Re your ACT, I wonder if cleaning its probe of carbon would have allowed a proper reading and testing. It appears IME that the Scorpio intake manifolds accumulate a really large amount of carbon deposits, thus possibly fouling the ACT sensor. If you haven't removed an intake manifold to see that you still get a hood sense of it by removing to clean the throttle body.

YMMV

[andyofcolumbusmerkur]

I blame the mid 90's Granada sensor(s).

[brokencase]

So, now we have, at least..., two instances of issues the EECIV should have set a code for, but didn't.

Yet you insisted in the case of SHIS that the clue to resolving it lies in a trouble code(s). Perseverancia vincit, well learned apparently.

Until you experienced a no-code diagnosis on your car, and then it seems the EECIV isn't as all-knowing as has been preached. Welcome to the club.

Re your ACT, I wonder if cleaning its probe of carbon would have allowed a proper reading and testing. It appears IME that the Scorpio intake manifolds accumulate a really large amount of carbon deposits, thus possibly fouling the ACT sensor. If you haven't removed an intake manifold to see that you still get a hood sense of it by removing to clean the throttle body.

YMMV

Ed, You kill me...

First off, we disagree on terminology. You call it SHIS. I call it EHIS - "Ed's High idle syndrome"
But the best terminology is to call it "Limp Home Mode" which I thought I had explained to you previously.
There are many cases of sensor failures where the EECIV will raise the idle to compensate.

Now we are confronted with the situation where such a case occurs and IF the owner actually checks the codes soon after the event.
It is quite possible an intermittent connection to a sensor could occur and the EECIV could later clear the error after finding subsequent readings are reliable. In such circumstances the best approach is to perform the wiggle test with the code reader. For which your response was "I have never done the wiggle test". No problem, I have also not found the need to perform the wiggle test. But then I have never experienced inexplicable EHIS. I have experienced high idle when my A/C diode went. But I was fully aware of the situation and had no need to check codes.

"No code" conditions are no stranger to me. I have experienced failed ECT in the past that never raised a code.
But this is understandable. Sensors can wander in their measurements due to age, but they may not go fully out of range to the point where the EECIV can detect it. Looking at the the EECIV logic in the document I had posted previously, the checks are very simplistic. in some cases they are only looking for and open or dead short to the sensor.

The point is Ed, that this is the very early years of ECM development at Ford. Naturally the error detection has improved over time. But we cannot consider our vintage to be optimized perfect from any point of view.

Now, with all the above being stated... I must admit I don't think I have resolved my issue. Yesterday after installing the new ACT it seemed my issues were resolved. But I think the engine might have been still warm.

I started it this afternoon and once again I experienced the stumbling until the car warmed up. I would say that the situation is improved a little but not much.

It is frustrating. However, I have not pulled codes or cleared them. I will try that tomorrow and see if things improve.

There was a mechanic up on youtube who nailed it on the head. "A lot of folks will see a code on the code reader that says "sensor out of range" and automatically assume that the sensor involved needs to be changed - nothing could be further from the truth"

An O2 sensor "out of range" could be indictive of a vacuum leak. Alternatively, a sensor could be out of range because the harness or connector associated to that sensor is bad.

With my particular problem, I am at odds with the EECIV diagnostics. To perform the KOER tests they require that the engine be warmed up first.

My problem does not exist when the engine is warmed up.

So...what is the issue? Stomping on the throttle right after starting cold yields stumble. Yet if the car warms up, only slightly, the problem disappears.

What would cause that?

[Fresh Air Inspector]

Hello Brokencase,

My issue is IDENTICAL to the one you are having. No issue when the weather is above ~10C (~50F), but as soon as it gets colder than that, the stumble returns. Basically in the Spring, Fall and early Winter (car is put away from December to April), the car needs to warm up for a few minutes before driving. If you hit the throttle gently when it is cold the stumble is there, give it more throttle coming off idle and it will stall necessitating holding the throttle open slightly to encourage it to start (engine appears to be slightly rich).

Today I pulled my spare ACT (new Standard AX3), as well as the original (Ford??? no markings on the body), the PO included with some other parts. I placed both of these against the head / intake manifold for an hour or so (cold engine, outdoor temp ~20C [68F]), and pulled the connector off the one in the engine (appears to be a Standard AX3). All temperature measurements were done with a digital infrared thermometer, resistance measurements with a DVOM.

Metal body of the ACT was at 22C (71.6F), for all three ACT sensors (car was in the sun);
New - 35.9K Ohm
Used - 36.2K Ohm
Installed in car - 36.1K Ohm

My assumption is the differences in resistance between the 3 ACT sensors isn't enough to affect the EECIV. Considering the ACT currently in my car (replaced in 2015 by PO ~8K km [5K mi]) is within tolerance and I recently (within 6 months, 2.5K km, 1.5K mi.), replaced the ECT, TPS and IAC, I have to assume the stumble is related to something else (EGR??).

PLEASE NOTE;
The aftermarket ACT has an electrical connection housing that is a mirror image of the factory ACT sensor (see picture ACT - 1R). If your ACT sensor has a black electrical connection housing and a white connector in the cable it is the original set up and you will need a 'kit' such as the Walker Products 21091002. If the ACT sensor has a white electrical connection housing and a black connector on the cable, it is an aftermarket sensor. I found it interesting that the thermistor on all the aftermarket sensors (RockAuto), is exposed whereas the Ford (??) originally installed in my Scorpio was inside the brass housing (see picture ACT - 2R).

ACT - 1R.jpg (203.52 KiB) Viewed 4967 times

ACT - 2R.jpg (212.99 KiB) Viewed 4967 times

Hope it helps.

[brokencase]

Hello Brokencase,

My issue is IDENTICAL to the one you are having. No issue when the weather is above ~10C (~50F), but as soon as it gets colder than that, the stumble returns. Basically in the Spring, Fall and early Winter (car is put away from December to April), the car needs to warm up for a few minutes before driving. If you hit the throttle gently when it is cold the stumble is there, give it more throttle coming off idle and it will stall necessitating holding the throttle open slightly to encourage it to start (engine appears to be slightly rich).

My situation is a little different. Even on a hot summer day the issue occurs. When I say "cold start" I mean starting with engine temp at ambient.

Also everything is fine if I slowly press the gas pedal. It is only when I stomp on the gas pedal I get...uh...uh..uh...then..vroom!

It typically doesn't stall. Just has that hesitation. Of course if I was driving the car then it might stall while under load, like pulling out into busy traffic, which is why I want to address this issue.

I don't know how it will behave in the winter, as the problem only developed this Spring/early Summer.
I suspect the problem will be a little worse in the winter.

Didn't get a chance to pull codes today. Will try tomorrow morning.

FWIW - O2 sensor is new. EGR is new. ECT is new. ACT is new.

Checked for vacuum leaks. Even used propane gas directed to suspect areas and no change.

Problem is I only have a narrow window of time to explore the problem, because only after a few minutes of running the problem disappears.
Then I have to wait for the engine to cool down before I can explore some more.

If there are no codes - I think I am going to re-check ignition timing.

[brokencase]

I'm thinking maybe I'm starting to see the early stages of fuel pump failure.

It was actually hard to start this morning...and I've noticed this on a few occasions in the past. It wouldn't go on the first or second try and then it finally started.

Check the description from this post...

viewtopic.php?f=29&t=8693&p=88435&hilit ... ump#p88435

"I think this may have some relation to a few other issues, namely a hesitation when hitting the accelerator from a stop until the car has been driven a good distance (usually highway driving will clear that up)."

I think I will check fuel pressure at the rail.

Now...where did I put that fuel pressure tester?

Might be fuel pressure regulator, but I doubt it. Definitely not looking forward to a fuel pump replacement project.

[brokencase]

Tested fuel pressure and I am getting 45psi KOEO and about 36 psi at idle, which is in spec.

I used the Harbor Freight fuel pressure kit. It worked OK, had to put some Teflon tape on the fitting to the gauge where it was leaking a little. But other than that is was fine.

Car also started fine today.

My hunch is a vacuum leak but I have checked quite extensively for this.

ECT and ACT I recently changed to address this issue to no avail.

But I have somewhat recently replaced a lot of the other items only because I came about replacements inexpensively and I figured I could keep what I pulled off as spares. EGR, O2, PFE, PVC, and TPS were changed.
Fuel Filter was changed in 2018.

[brokencase]

Pulled codes this morning, both KOEO and KOER. No codes.

BTW, I ran the code tests first with the engine cold in the hope that maybe the problem would be detected during the "stomp on the throttle" phase of the KOER test. It actually stumbled and hesitated when I stomped on the throttle. In this instance I received only an ECT error code 21 (ECT out of range)

However I repeated both KOEO and KOER with the engine fully warmed up and there were no error codes.

I re-double checked that EGR was not leaking at idle. It is OK.

Sprayed some ether around to look for vacuum leaks and found none.

So... Where to look next?

I don't believe it is IAC because the EECIV does a very substantial idle variation test when performing KOER and that seemed to run fine.

I ordered a NOS MAP sensor a few days ago and I am waiting for that to arrive.

Still have not checked ignition timing.

Searched through my very complete Scorpio TSB collection and there was one TSB regarding cold hesitation related to an EECIV strategy change to be performed under warranty. Not sure I have that but I don't suspect this because this problem did not previously exist on my car.

There is mention about checking timing advance for hesitation and also to check the ignition coil resistance. In addition, the need to check MAP.
There is also mention of cleaning the throttle body. But I have done that recently.

The only other thing I can think of that would be an issue is clogged fuel injector(s). Really? Clogged injectors at 87K miles?
I would think that I would have other drivability issues if this were the case. But with more ethanol in the fuel today perhaps this could be a problem.

It bears mentioning that I have, on a few occasions, ran high quality fuel injection cleaners. I think when I first acquired the car I ran a large bottle Royal Purple through. Later on I had purchased a couple of "3M intake cleaner kits" from Ollies near me. These come with fuel injection cleaner.
Like this..
https://www.ebay.com/itm/401819230343

That is an expensive kit. But Ollies had them at a blowout price like around $10 as I recall. I should have bought more of them!

[john keefe]

I'm gonna' guess VAM rheostat needs cleaning, and/or it's developed a groove in the track where quick cold throttle blips allow the needle to skip over the most worn section (probably 1500-2K rpm). Maybe the needle itself is a little sticky, and it "jumps" in rebound during the first few swipes, then eventually frees up and sweeps smoothly through the whole range, making it seem like it's "warmed up."

[Fresh Air Inspector]

Hello Brokencase,

You are one step ahead of my thoughts with your ordering a NOS MAP sensor. This sensor could be dirty or sluggish from the EGR crap in the manifold causing it to be 'slow' for the first few miles. You've already replaced all the other sensors except the TFI. Mind you it is possible that the timing may be slightly off as you surmised earlier. At any rate, looking forward to the outcome of swapping out the MAP.

Hello John,

I assume by VAM (Vane Airflow Meter), you mean the TPS (Throttle Position Sensor)? The Scorpio doesn't use a VAM. Also, Brokencase already replaced the TPS.

Interesting thread.

[john keefe]

I assume by VAM (Vane Airflow Meter), you mean the TPS (Throttle Position Sensor)? The Scorpio doesn't use a VAM. Also, Brokencase already replaced the TPS.

Yeah, oops. Was reflecting on recent similar MAM problems with the 5.0L XR (crap C&L meter and sensor, cured with Ford 75mm MAM), and got mentally side-tracked into linking the discussion with XR's. Never mind...

[andyofcolumbusmerkur]

Where I live they change the gas around this time. I have heard people complain about it but I have never been able to notice any difference.