Escalating Hesitation-Then-Jerk-Forward Issue

Maintenance/Repairs
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21

Update. Just got back from the mechanic. He and I drove it around for 15 minutes, with me driving. Couldn’t get it to reproduce itself. Car drove perfectly the whole time.

The mechanic said he tested everything, checked for codes, drove it around with the machine plugged in that would have indicated if there was a problem. Nothing.

I’m really worried driving it around. If it suddenly decelerated at 15 MPH which was enough force to throw my dog off the seat, what would happen if it does it at 30 or 40 MPH??

One other thought: could it be the belts themselves? That is, what if whatever keeps tension on the drive belts is malfunctioning and causing the belts to loosen or tighten randomly? Is that possible?

Thanks!

22

The accessory belt(s) could be temporarily removed and each pulley it goes around turned manually, trying to ascertain if there’s a hitch in the rotational movement, grinding noise, etc. Two of the pulleys may have clutches on them, the fan pulley, and the AC compressor pulley. The problem might not occur until the clutches are activated. But maybe they have a way to activate them for testing. Another idea, there may be a problem with the throttle positioning getting confused. On a 2003 you may not have the drive-by-wire technology used in many newer vehicles, but you’ll at least have a throttle position sensor that can be tested. A throttle positioning problem wouldn’t explain the squealing noise tho.

If all else fails, ask them to keep the car for a week or two, one of their shop crew can drive it to and from work every day. You can rent a car in the meantime, or maybe they’ll give you a loaner. It sounds like your shop is working with you to get to the bottom of it. I expect something will turn up if you keep on keeping on.

23

Actually, this shop gives me a loaner. They have a couple of beater cars that have problems but run that they give out as loaners when they have to keep your car a few days. So they had given me a loaner, and I asked the mechanic if he wanted to keep my car for another day, to see if it happens, and he said he didn’t see the point, that it was driving perfectly. He said if I get a check engine light that would be very helpful.

I drove the car a little tonight. Still driving perfectly. No problems at all.

24

What’s needed for diagnosing problems like this is a monitor box which the shop would hook up to the various sensors. It would automatically record the readings vs time, stored in memory. When the driver noticed the symptom happening, they’d press a button on that box. The recordings would be saved for later review by the shop. Such a box exists for people with heart problems, called a Holter Monitor I think. Unfortunately there’s nothing similar I know of available for diagnosing intermittent problems w/ automobiles.

25

Chrysler’s Co-Pilot has been around for 25 years however I’m not sure your down shifting glitch will show up in a capture.

26

That’s interesting. I’ve never heard mention of that gadget here before now. I’ll have to look up the specs.

Edit: Found an internet version of the Co-Pilot instruction manual. The copy quality isn’t very good on the photo of the output display examples, so it is hard to tell exactly what functionality it offers. But it definitely seems to be a step in the right direction for intermittent problem diagnosis. Good on the Chrysler engineers for coming up with such a good tool! If the OP continues to experience the symptom, find a shop having this tool, give it a try.

http://kb.dcctools.com/index.php?View=afile&EntryID=139&AttachID=183

“First: A service technician programs the Co-Pilot Data Recorder and
installs it, along with the Remote Controller Trigger, in the customer’s
vehicle.
Second: The customer drives the vehicle. When the intermittent
problem occurs, the customer simply presses a Record button on
the the Remote Controller Trigger to capture the data. The Co-Pilot
records approximately 45 seconds of engine data. From one (1) to
three (3) separate recordings can be made. The Co-Pilot always
saves the three (3) most recent recordings.
Third: A service technician removes the Co-Pilot components from
the vehicle, uploads the recorded data to the MDS1 or MDS2, and
begins vehicle data analysis.”

27

Car’s been running great since the other day. Not an ounce of trouble.

I had another thought about this, Maybe you guys can tell me what you think about this, if you think it’s plausible.

What if some debris got stuck in the fuel line? That would cause the frequent hesitate-then-go symptoms that I started experiencing a few months ago. Those symptoms got more frequent. Not sure what would cause that, unless the debris got stuck further into the fuel line or something.

Then there was the second symptom, slowing down of the car while I’m driving. That could also be caused by the debris, perhaps if it moves–either within the fuel line or the fuel pump, perhaps–and blocks more fuel.

Then, last, was the most troubling symptom, the sudden and complete deceleration for a moment that caused the dog to go flying off the seat, followed by a grinding sound for a few seconds. What if, when that happened, the debris momentarily completely blocked the fuel line, but was then released from the fuel line by the pressure of the fuel being pushed by the fuel pump? The car would suddenly stop for a moment, since it would be in gear, but would have zero fuel.

But that still wouldn’t explain the squealing sound. At first I thought, perhaps the sound was from the belts screeching to a halt. But the sound happened AFTER the car started moving again, not when it was stopping. So that doesn’t explain it.

Anyway, that was a thought I had, that perhaps some debris was stuck in the fuel line or fuel pump for several months, but then finally worked itself out after momentarily completely clogging the fuel line, causing the fuel pressure to build up behind it, which then expelled it into the spark plugs which incinerated it.

That would explain why my car has been driving perfectly well since that incident. But, again, still wouldn’t explain the squealing sound.

What do you guys think?

28

The fuel pressure at the input to the injectors has to be more or less constant for the fuel injection system to work correctly. the reason is that the person who programs the amount of fuel to inject uses a formula similar to this

Volume of Fuel injected = Injector pulse interval * K

where K is a constant involving the fuel pressure and the specified characteristics of the injector. i.e. the programmer assumes the injector always injects a certain volume of fuel per m-second of injection pulse interval. If the fuel pressure varies, that formula no longer applies and the computer thinks it is injecting a different amount of fuel that it actually is. Fuel pressure is a simple test, so it should be something to investigate , should the problem return. Sometimes the shop will strap a fuel gauge to the outside of the car and watch it while they do a test drive. If the pressure drops coincident with the symptom, they know they have a fuel pressure problem. That could be caused by a faulty fuel pump or debris blocking the intake to the pump etc.

Faulty fuel pumps can make a squealing sound, but even if the fuel flow shut off completely for some reason, that wouldn’t likely explain such a rapid acceleration as you are talking about.

29

Thanks for the feedback. That’s good to know. But if the car is in gear and fuel gets cut off instantaneously, wouldn’t that cause a rapid deceleration? Seems the only way it would gradually slow down would be if there was still some fuel being sent to the engine, no?

30

Most engine computers completely cut off the flow of fuel when you let your foot off the gas. This is to reduce emissions and improve mpg. So you can do the experiment yourself, drive down the road at a steady speed, then let your foot off the gas. At that point there is absolutely no gasoline being injected, and the spark plugs may still be getting sparks, but the cylinders aren’t firing.

When I do this experiment w/my manual transmission Corolla at 35 mph in 3rd gear, the deceleration effect is very gradual. No jerking-forward sensation at all. As I coast nearly to a stop, still in 3rd gear , around 5 mph, I can feel the effect of the injectors start injecting gasoline again, which feels like a slight acceleration.

31

Can you clarify this a bit? Why are the injectors injecting gasoline again if your foot is off the gas? When I drove a manual transmission, if I took my foot off the gas in 3rd gear, it would eventually come to a stop and then the engine would stall out if I didn’t take it out of gear.

Thanks.

32

You may be feeling the transmission shifting.

33

Just thought I’d note that, after several days of the problem being completely gone, it came back a little today. AND a new symptom manifested.

First, when I pulled out of my parking spot today, after the car sitting overnight, it did the hesitate-then-go thing. My foot was barely touching the gas, and it sputtered, like it was going to die out, then went. Then sputtered, then went, etc. Did it three times, and then it was fine.

Then, later in the day, a new symptom: as I was slowly backing out of a parking space, I heard a clunking sound about two times a second from the front of the car. It continued until I put the car into drive, then it stopped. Going into reverse again, the problem didn’t come back. Checked the oil and transmission fluid. Both were fine.

So, anyway, there’s some info that the car’s not out of the woods yet with the original problem, and there seems to be something else going on, which may or may not be related to the original thing.

34

holy cow dude… that’s a doosy

35

yeah… :frowning:

36

The computer stops injecting gas if it determines for that driving situation no gas in needed. Like when slowing down with your foot completely off the gas from 35 to 15 mph in third gear, approaching a stop light, no gas is needed. The car is coasting to a stop, assisted by engine compression. At 15 mph the computer then decides it must inject gas, otherwise the engine rpm is so low, with no gas at all, it will stall. Of course if the driver doesn’t push the clutch pedal in at some point, in 3rd gear, when the car comes to a complete stop the engine will stall no matter what the computer does with the injectors.

37

OK, thanks for clarifying.

BTW, following up from my note from yesterday, about the symptoms starting to resurface, today it did almost the exact same thing. It was the first drive of the day. I pulled out of my parking spot; was fine. Then started to go forward very slowly down a slight incline. When coasting, car was fine. If I just barely touched the gas pedal, car would jump forward, then would be fine after that. Did that about three times. Then was fine for the rest of the day.

This is almost the same as yesterday. Difference is, yesterday, when I touched the gas pedal, car sputtered like it was going to die, then lunged forward. Today, no sputtering. Just a lunge forward when I barely touched the gas pedal, then fine until I took my foot off the gas pedal. Then it would be fine while coasting, and then lunge forward when I barely touched the gas pedal. Then, as noted, after about three times it was fine and functioned normally for rest of the day.

So almost the same as yesterday, but a little different.

38

Can’t recall if I already mentioned this, but I had a lunging problem w/my Corolla a while back, which I traced to clogged fuel injectors. It was only noticeable in slow speed driving situations, around 10-20 mph. Like if I was slowing down to turn a corner in neighborhood driving, I’d let my foot off the gas and it would jerk a little rather than gradually slowing down, then when I stepped on the gas slightly after the turn it would jerk a little rather than gradually speeding up. I think the computer was having a hard time metering out the correct amount of fuel b/c due to the injectors being slightly clogged. Like if you had a sprinkler in your garden slightly clogged up, it would be hard to get it to spray just a little, but might well work fine on full force.

With the symptom you are reporting, it would make sense to check the throttle position sensor too of course.

The lunging problem I had wasn’t so bad it would knock my dog to the floor though. But whether a lunge would knock a dog to the floor probably depends on the size of the dog. A smaller dog I’d guess is more likely to be knocked to the floor during a lunging stop.

39

Yeah, the lunging thing sounds like what I’m experiencing. First thing the mechanic recommended was to do a fuel system service (cleaned throttle, intake, air flow injector, hooking it up to some machine or whatnot). And last time I took it in, he said he cleaned something else for me, I think it was the throttle position sensor, not sure.

Keep in mind that I may be experiencing several issues, not just one. So the lunging is one thing. The sudden stop which caused my dog to fly off the seat may be completely unrelated. Not sure.

And there’s also the deceleration when going about 30-40, which has no ill effects, except that it’s odd.

These all may be related or may not be.

Oh, and there’s also the clanking sound I noted above, which only happened once, yesterday, and only until I shifted from Reverse to Drive. Then it stopped.

So not sure if there’s one or multiple issues here.

40

It does sort of sound like there are multiple problems, which makes the diagnosis more complicated. You might try just running a couple cans of fuel injector cleaner through the system, the kind you just pour into the gas tank. If it helps the jerking problem, you at least know you are on the right track. Techron I think is often recommended here for that. I used a product called “Clean Power” as I recall, but the same idea, pour it in the gas tank.

Edit: OP, have you tried the experiment slowing down, foot off the gas pedal, from 35 mph to 5 mph, when approaching a stop sign in 3rd gear, try to determine if you can feel the injectors turning back on again as you approach the stop? It’s very easy to feel that on my manual transmission Corolla. When I was having the jerking problem it was much more pronounced. Now it is working correctly, the effect is perceptible, but no sense of jerking forward. Might be diagnostic to give it a go anyway. I think you said your vehicle in an automatic, so doing that experiment might be more difficult. But you should at least be able to select a fixed gear. You can’t turn off the torque converter tho, which b/c of it slipping as a normal course of operation should tend to mask the effect I think.