Hesitation in warmer weather

[FNFAL]

I have a '99 explorer sport sohc with 230,000 miles.

Early last fall it started hesitating when accelerating from a stop. Like no fuel or something. It only did it when the weather was warm, like over 70F. Today it started doing it again and this is the first day over 70 degrees since last fall. It ran fine all winter, didn't do the hesitation. I put 90 miles a day, six days a week on it, I deliver mail from it, lots of stop and go.

Mechanic looked at it last fall and couldn't be sure what was causing it. I took a gamble and replaced the IAC valve and then later the mass air flow sensor, neither fixed the issue.

What would cause this?

 

[XLTrunner]

My '98 has had similar instances where, when I go to pull out from a stop (after having been driving the truck for however many miles beforehand), it will suddenly fall on it's face for a split second and then catch hold and accelerate. It's infrequent and I can't say I've noticed it at any certain outside temperature; although it usually is when it's warmer out. There have been several threads on here regarding this issue and nobody seems to have any idea; other than the usual check fuel filter, fuel pump, IAC, MAF, etc.

Anyone else?

 

[FNFAL]

yeah it's weird, maybe it's some kind of bug in the computer, it gets confused and starves the engine for fuel for a few moments? Guess I'll have to wait till the problem becomes more than intermittent to be able determine the cause.

 

[XLTrunner]

Happened to me once again yesterday after having driven 240 miles that had me driving everything from freeways to rural hwys to city streets along the way with many stops at intersections. Not one problem until I was a couple miles from home...when it briefly hesitated upon acceleration after a stop. I, too, think it's just a glitch in the computer. Truck ran fabulously the whole way, otherwise. By the way, it was in the upper 60's F at the time.

 

[jlrohio]

What exactly do you mean by hesitation? What are symptoms are present during the hesitation?

I have a 99 OHV - 155,000. I have had an intermittent "hesitation" issue for years. It usually only occurs about 1 or 2 times a month. Usually, it's from a stop...as I give it a little gas to accelerate, the RPM's will shoot up to 3,000+ (it seems as though the shifter was moved to Neutral while continuing to press on the gas pedal).

This hesitation will last for about 1-3 seconds before it will finally "catch" and start moving. No codes, no Check Engine Light - nothing. The vehicle will then seem fine for weeks on end before occurring again. I've been the primary driver so it's something I've gotten used to. My family has noticed it a time or two when they were in the vehicle.

Yesterday, my son was driving it on the highway (at highway speeds) and he said the same sort of thing happened to him...he was just driving along - went to tap the gas to maintain speed/accelerate and it hesitated on him - the RPM's shot up, etc....he said he shifted it into Neutral and then back into Drive and it went back to driving normal.

I'm going to continue searching through these threads for hesitation issues...wish I could find out what might be going wrong to this rare "intermittent" issue.

Another thing, I'm guessing that OHV and SOHC would not be relatable to this issue as they have different setups???


During your "hesitation" cycles, is there a noticeable increase in the RPM's??

 

[Hatcher686]

What exactly do you mean by hesitation? What are symptoms are present during the hesitation?

I have a 99 OHV - 155,000. I have had an intermittent "hesitation" issue for years. It usually only occurs about 1 or 2 times a month. Usually, it's from a stop...as I give it a little gas to accelerate, the RPM's will shoot up to 3,000+ (it seems as though the shifter was moved to Neutral while continuing to press on the gas pedal).

This hesitation will last for about 1-3 seconds before it will finally "catch" and start moving. No codes, no Check Engine Light - nothing. The vehicle will then seem fine for weeks on end before occurring again. I've been the primary driver so it's something I've gotten used to. My family has noticed it a time or two when they were in the vehicle.

Yesterday, my son was driving it on the highway (at highway speeds) and he said the same sort of thing happened to him...he was just driving along - went to tap the gas to maintain speed/accelerate and it hesitated on him - the RPM's shot up, etc....he said he shifted it into Neutral and then back into Drive and it went back to driving normal.

I'm going to continue searching through these threads for hesitation issues...wish I could find out what might be going wrong to this rare "intermittent" issue.

Another thing, I'm guessing that OHV and SOHC would not be relatable to this issue as they have different setups???


During your "hesitation" cycles, is there a noticeable increase in the RPM's??

If its an automatic transmission, this sounds like the tranny is going out. I had the same issue, getting on the highway and all of a sudden my rpm's raised and then it finally grabbed a gear with a hard jerk. It started happening more frequently. Couple months later tranny went out, but I found that 1st gear would work. Just an idea, hope this helped. If it is a tranny car-parts.com is a great site to get used car parts. I got mine for $750 with a $100 core return.

 

[koda2000]

Super wild-ass guess - upstream O2 sensors. They're good for around 100,000-120,000 miles (the heated ones) or maybe the coolant temp sensor?

 

[jlrohio]

If its an automatic transmission, this sounds like the tranny is going out. I had the same issue, getting on the highway and all of a sudden my rpm's raised and then it finally grabbed a gear with a hard jerk. It started happening more frequently. Couple months later tranny went out, but I found that 1st gear would work. Just an idea, hope this helped. If it is a tranny car-parts.com is a great site to get used car parts. I got mine for $750 with a $100 core return.

Thanks for your input....hopefully, it is not the transmission soon to go issue. I've had the issue off and on for about 8+ years. Although, never on the highway. We'll keep a watch on it.

 

[jlrohio]

Super wild-ass guess - upstream O2 sensors. They're good for around 100,000-120,000 miles (the heated ones) or maybe the coolant temp sensor?

Would issues with an O2 Sensor tend to throw a code if anything was wrong with them?

Also, just curious as to how the coolant temp sensor could be related to a shifting/hesitation issue? Is it based upon the expected temp of tranny fluid - after all, the tranny fluid does go through the radiator for cooling.

 

[koda2000]

Would issues with an O2 Sensor tend to throw a code if anything was wrong with them?

Also, just curious as to how the coolant temp sensor could be related to a shifting/hesitation issue? Is it based upon the expected temp of tranny fluid - after all, the tranny fluid does go through the radiator for cooling.

O2 sensors don't always through codes when they go bad. As far as the temp sensor, I was was thinking about the air temp sensor and the coolant temp sensor, because they effect how much fuel the PCM delivers. More in colder weather, less in warmer weather. Thet usually will throw codes if bad.

Codes are almost all emmisions related and occur when any of the dozen or so sensors reports something out of electrical range back to the PCM. A sensor that reports misinformation back to the PCM but is still within it's acceptable range will not throw code.

Try rubbing a finger inside your exhaust pipe. If it comes out black a sooty you're running too rich (too much fuel). That's often due to the upstream O2 sensors not doing their job.

 

[Rickter Spatz]

My hesitation started I believe after fuel pump/sender replacement and it is pretty rare. I use cruise control on the interstate and noticed it buck and slow down a little once - in a corner I think. Another time I had it die when coming up a longish hill to a stop sign at top. Another time it died on a flat highway after cruising pretty fast, slowing as coming into town area, and stopping for the sign. Motor wasn't running. Turned key and it fired no problem.

Maybe the last time or 2 I've felt it coming on and get out of and then back into gas pedal. Takes off. Not happening very often so waiting and seeing for now.....plugs & wires relatively new, PVC, fuel filter, pump, and sending unit. Pressure seems okay. Haven't messed with pressure regulator as thought I read that's not usually the culprit. Also sometimes if hasn't been driven for 2-3 days seems to like some gas pedal before starting...

 

[Bob Swaters]

I am having a similar hesitation or stumble that occurs once in a while, usually on very hot days in stop and go rush hour traffic, or when taking off from a red light with very light throttle. I know I am due for a fuel filter change, don't know if it could be a factor.
I recently ran FORscan and it picked up a code for tps sensor, reading high at idle or something like that. I checked for voltage at the sensor and it was right on the money. My mechanic friend says a tps can get worn and develop "dead spots", usually at idle position or just off idle, as this is where most wear occurs. This might cause a temporary loss of voltage signal and a stumble or hesitation. I am planning on replacing mine soon, as I am pretty sure it has never been replaced in 166k miles.

 

[bigred4x4]

I have the same problem with my focus when it's hot and especially while running ac you could stomp the gas from a stop and it just kinda buzzes and spaces off for a few seconds then takes off but harder than normal the idle is also rough and it vibrates really bad.. It's done this for years...I know this doesn't help because it's a totally different vehicle but probably caused by similar problems iv replace o2 sensors and various other things I've just learned to live with it but would love to find out a solution.

 

[sjana]

I am having a similar hesitation or stumble that occurs once in a while, usually on very hot days in stop and go rush hour traffic, or when taking off from a red light with very light throttle. I know I am due for a fuel filter change, don't know if it could be a factor.
I recently ran FORscan and it picked up a code for tps sensor, reading high at idle or something like that. I checked for voltage at the sensor and it was right on the money. My mechanic friend says a tps can get worn and develop "dead spots", usually at idle position or just off idle, as this is where most wear occurs. This might cause a temporary loss of voltage signal and a stumble or hesitation. I am planning on replacing mine soon, as I am pretty sure it has never been replaced in 166k miles.

Hi Did you find any solution for this?

 

[sjana]

Hi Did you find any solution for this?

I have a '99 explorer sport sohc with 230,000 miles.

Early last fall it started hesitating when accelerating from a stop. Like no fuel or something. It only did it when the weather was warm, like over 70F. Today it started doing it again and this is the first day over 70 degrees since last fall. It ran fine all winter, didn't do the hesitation. I put 90 miles a day, six days a week on it, I deliver mail from it, lots of stop and go.

Mechanic looked at it last fall and couldn't be sure what was causing it. I took a gamble and replaced the IAC valve and then later the mass air flow sensor, neither fixed the issue.

What would cause this?

I am having a similar hesitation or stumble that occurs once in a while, usually on very hot days in stop and go rush hour traffic, or when taking off from a red light with very light throttle. I know I am due for a fuel filter change, don't know if it could be a factor.
I recently ran FORscan and it picked up a code for tps sensor, reading high at idle or something like that. I checked for voltage at the sensor and it was right on the money. My mechanic friend says a tps can get worn and develop "dead spots", usually at idle position or just off idle, as this is where most wear occurs. This might cause a temporary loss of voltage signal and a stumble or hesitation. I am planning on replacing mine soon, as I am pretty sure it has never been replaced in 166k miles.

Hi Did you find any solution for this?

I have a '99 explorer sport sohc with 230,000 miles.

Early last fall it started hesitating when accelerating from a stop. Like no fuel or something. It only did it when the weather was warm, like over 70F. Today it started doing it again and this is the first day over 70 degrees since last fall. It ran fine all winter, didn't do the hesitation. I put 90 miles a day, six days a week on it, I deliver mail from it, lots of stop and go.

Mechanic looked at it last fall and couldn't be sure what was causing it. I took a gamble and replaced the IAC valve and then later the mass air flow sensor, neither fixed the issue.

What would cause this?

I am having a similar hesitation or stumble that occurs once in a while, usually on very hot days in stop and go rush hour traffic, or when taking off from a red light with very light throttle. I know I am due for a fuel filter change, don't know if it could be a factor.
I recently ran FORscan and it picked up a code for tps sensor, reading high at idle or something like that. I checked for voltage at the sensor and it was right on the money. My mechanic friend says a tps can get worn and develop "dead spots", usually at idle position or just off idle, as this is where most wear occurs. This might cause a temporary loss of voltage signal and a stumble or hesitation. I am planning on replacing mine soon, as I am pretty sure it has never been replaced in 166k miles.

Hi Did you find any solution for this?

 

[donalds]

Start a new thread
You will yield better results

 

[jlrohio]

@sjana I never found a solution to my 1999 Ford Explorer hesitation issues - usually from a stop sign/light.

My vehicle is now approaching it's 25th year (woo hoo - Antique plates and no more state inspection required!).
She's driven maybe once or twice a week now and she is consistently very reliable.
A few issues over the years and all have been repaired or solved...except for this one hesitation issue, which forever will probably remain elusive. No codes, no nothing.

 

[EB4X]

@sjana I never found a solution to my 1999 Ford Explorer hesitation issues - usually from a stop sign/light.

My vehicle is now approaching it's 25th year (woo hoo - Antique plates and no more state inspection required!).
She's driven maybe once or twice a week now and she is consistently very reliable.
A few issues over the years and all have been repaired or solved...except for this one hesitation issue, which forever will probably remain elusive. No codes, no nothing.

JLROHIO... I almost guarantee your issue is a subpar(clinging to life) o2 sensor, your statements here are exactly what mine was doing (but consistently):
"as I give it a little gas to accelerate, the RPM's will shoot up to 3,000+ (it seems as though the shifter was moved to Neutral while continuing to press on the gas pedal)."
"This hesitation will last for about 1-3 seconds before it will finally "catch" and start moving. No codes, no Check Engine Light - nothing."
Yep, no CEL, codes etc. Being a consistent issue with mine made it easy to determine it was an o2 sensor and which one.....I disconnected all of mine at their harness/plug putting system in open loop and that causes the Ford PCM to run off a basic preset....issue completely disappeared with this!, thus diagnosing problem was with "a" o2 sensor....then plugged them in one at a time / test drove until bad one was re-connected and symptoms were then immediately reinstated.....bingo!