Escalating Hesitation-Then-Jerk-Forward Issue

Maintenance/Repairs
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41

Thanks for the tip, George. The first thing the mechanic recommended was to have a fuel system service done (hooked it up to some machine and cleaned throttle, intake, air flow injector, etc.). Paid him $130 for the service. Do you think the fuel injector cleaner might still make a difference? If you do, then I’ll try it. But just wanted to point out that I’d already had that service done. Thanks.

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?

No, I haven’t. But I have slowed down and haven’t felt anything. But then, when I touch the brake, there’s sometimes a slight jerk, which could be a separate, brake-related issue. I’m going out in a minute and I will try this 35 to 5 thing and see if I notice anything. I’ll put it into L when doing it, since you say I should use a fixed gear.

BTW, when baking out of my spot yesterday (which is when the problem usually manifests), when I came to a stop after going in Reverse, and was about to put it into Drive to go forward, the engine died. This has happened before a few times, though it’s not frequent. So definitely a fuel flow issue from somewhere.

42

Your comment is a little inconsistent. A fuel system service wouldn’t normally involve the throttle body or throttle valve or the intake manifold. Those are air intake items. Not sure what an air flow injector is. You may be referring to the mass air flow sensor, which would make sense to clean it as part of the other as it is accessible at that point, but that isn’t a fuel system service item either. A common “fuel system service” item would be to clean the fuel injectors. For that shops will either just add some injector cleaner to the fuel tank , or they’ll hook up a machine to the fuel rail and inject a different type of cleaner directly into the injectors. The second method is reported by the experts here to work better, but I personally have no experience w/that method.

Whether that is caused by a fuel flow issue remains to be determined. There’s obviously something wrong, but it could just be the idle rpm system is not working correctly. The computer jumps through a bunch of hoops to keep the engine rpm high enough to prevent stalling, but not so high that it causes a drivability problem. And when the engine is cold, it has to jump through more hoops than when it is warm. In some vehicles the computer is more involved in all that than in other vehicles. But even in my 25 year old Corolla, if I turn the headlights on the computer increases the idle rpm to prevent stalling.

43

Yes, that’s what he did. I remember he said they hooked it up to a machine and injected cleaner directly into the injectors. But then he listed some other things that were cleaned and I wrote them down. It’s possible that I wrote them down wrong, as he was talking a little fast and has an hispanic accent. So maybe I got something wrong. But the part about them hooking it up to a machine and injecting fluid directly into the injectors I remember clearly.

So, with that being said, do you think it’s still worth trying a few bottles of fuel injector cleaner?

Whether that is caused by a fuel flow issue remains to be determined. There’s obviously something wrong, but it could just be the idle rpm system is not working correctly.

Good point.

Speaking of that, I did the test you recommended. I found an empty street, put it into 3rd gear, got up to 35 MPH, and then let the car gradually reduce its speed to less than 5 MPH, without applying the brakes. The car got down to 3 MPH and stayed there. No signs of symptoms of anything not working properly.

That being said, these symptoms that I’ve been experiencing only happens when I first start driving the car after it’s been sitting for a while. After a minute or two, the car is functioning normally, and touching the gas pedal when going slowly does what you’d expect it to do without hesitating or jerking forward.

So it’s quite possible that by the time I did my 35-to-5 test, the car was functioning normally. And after I did the test, it was functioning normally. So I’m not sure that the test results are valid, since the car was most likely out of the the problematic timeframe by then.

44

You have listed so many quirks that it is difficult to explain what one part is failing. If this is your concern replace the idle air control motor, this device maintains the engine speed at idle.

It is common practice to clean the induction system (throttle body, intake manifold and intake valves) and the fuel injectors during a fuel system service, this has been going on for 20 years.

45

Thanks for the reply. My concern is mainly what it does after it’s been sitting overnight: touch the gas and it hesitates then jerks, sometimes two times in a row. Release the gas, and it coasts fine. Touch it again, same. This problem lasts anywhere from 30 seconds to 5-10 minutes, then the car is fine for the rest of the day usually. This is the main thing.

The car dying when going very slow I’m assuming is related to the above issue. But it’s not a major concern for me. The above issue is the main concern.

That being said, the one time (which I described in an earlier post) when I was going about 15 MPH and the car suddenly stopped for a moment (causing my dog to fly off the seat), and then went again, accompanied by a squealing noise for 2-3 seconds, is a major MAJOR concern, since, obviously that’s a serious safety issue. But that only happened one time.

Those are the main issues that I’m concerned with. I think if I can resolve the first issue, the others will probably fall into place.

46

I don’t have an answer to your sudden deceleration and lunging forward issue. Never mind the doggy thrown off the seat, worry about your own safety and the safety of drivers around you. Can you imagine what might happen at high speed and the car suddenly decides to decelerate?

47

Can you imagine what might happen at high speed and the car suddenly decides to decelerate?

Probably nothing to the drivers around me, since, when it happened, it only lasted for a moment (enough to throw my dog off the seat), and then the car resumed normally (albeit with a squealing sound for a few seconds). The greatest danger is to myself (and my dog) if it happened at a high speed.

My mechanic didn’t seem too worried about it, which may or may not be a good thing. He took the car home after I described the sudden deceleration to him and drove it on the freeway. But, yes, this concerns me. Fortunately, it’s only happened once, and I believe whatever’s causing the hesitation and lunging forward thing is related to that. So hopefully both will be addressed at the same time.

48

Update. I drove it last night after it had been sitting idle for 5 hours, and it didn’t manifest any of the symptoms. But I know it regularly did after it had been sitting for 12 hours. So somewhere between 5 and 12 hours is the amount of time needed for it to sit so that it manifests symptoms.

So this shows that the problem has nothing to do with the engine being cold. The engine was certainly cold. But something about having it sit for extended period of time causes these symptoms.

49

Most of what you are experiencing points to some problem in the throttle body area. Sticking throttle butterfly valve, idle air control, or throttle position sensor. Has the throttle position sensor function been independently bench-test verified yet?

Maybe a little of my own experience would be helpful. When I had a similar problem on my Corolla – in my case I had a higher than normal idle rpm too – besides the fuel injector cleaning, I removed the throttle body, cleaned all the gunk off its backside, and tested the functionality of all that stuff on a nice brightly lit bench. I discovered several problems:

  • egr and pcv gunk was preventing the throttle valve from closing consistently to the same angle
  • the idle air control device was faulty
  • the throttle position sensor (switch actually in my case) wasn’t calibrated correctly

I fixed the other stuff, but wasn’t able to fix the idle air control device b/c the replacement part is not available. My only option was to replace the entire throttle body with a junk-yard part. That’s not happening. So I blocked off the air passages and disabled it. This has a downside that without an idle air control function I have to step on the gas pedal a little when it is really cold in the winter to prevent the engine from stalling at stop-signs the first quarter mile or so in the morning. But since I live in San Jose, really cold weather is seldom a problem. If I lived in North Dakota I’d have to fix it properly. When I did all this, I also replaced the fuel filter. And I brought all the routine maintenance up to date, new plugs, new distributor cap & rotor, new spark plug wires, checked the valve clearances, set idle rpm and ignition timing. I later discovered I had a thermostat that wasn’t closing fully, so I replaced that too, and did a full cooling system service. After all that, the problem was completely eliminated. I expect, given the stubbornness of the symptoms, you are going to have to go down a similar path.

Edit: Since you’ve already had the pro-version of the fuel injector cleaning treatment, I don’t see much upside to doing it again with the pour in the tank method. At this point if you have a fuel injector problem they will probably have to come out and be bench tested.

50

Me thinks it is vehicle trade time.

51

Me thinks it is vehicle trade time.

The car only has 93,000 miles on it. Hate to give up on it, especially if it’s something that can be fixed for < $1,000. Just wish could figure out what’s going on.

52

No, I don’t think so, though the mechanic said he tested everything. Not sure what “everything” includes though.

I have to say that, while I commend you for doing such a thorough job in getting your car issue resolved, given that I wouldn’t be able to do that myself, but would have to pay someone to do it, if my car needs all of that, I’d have to agree with the other poster, that maybe it’s time for a new car. But I’m not giving up yet. Maybe it’s something simpler. After all, only has 93,000 miles on it.

Update on the situation. Though I posted last that the hesitate-then-jerk issue didn’t happen after sitting for 5 hours, I tested it again this evening, after it had been sitting for over 16 hours, and it didn’t do it then either. So can’t rely on previous conclusion that 5 hours doesn’t cause it to happen. The problem may be on hiatus, as it was before for a few days.

However, you may recall that previously it once made a “clunking” sound when going in reverse, about two times a second, which stopped when I put it into drive. (See post #33 in this thread.) Only happened that one time. But today it happened again. Backed out of parking spot in reverse and heard clunking sound.

I put the car into Park, so I could pop the hood and get a closer look. But when I did that, the sound went away. So I had to keep it in Reverse with my food on the brake to get the sound. So I made a brief video of the sound. Pointed the camera towards the engine, and then towards the back of the car, to be clear about where it was coming from. It’s definitely coming from the engine. Sounds just like what happened once when I ran out of oil. Only I’m sure I’m not out of oil. Oil is full.

Anyway, sound continued, but then, when I went into Drive, it continued for a short while, unlike last time where it went away when I went into Drive. Kept making sound in Drive for about 30 seconds. After that, didn’t make sound anymore, either in drive or in reverse.

Anyway, here’s a link to a little 8 second video that shows that clunking sound when it happened briefly earlier:

Thanks!

53

I can’t speak to how long it would take for an experienced mechanic with a shop and lifts etc to do all those things on your vehicle, but I’m just as a driveway diy’er, I doubt it took more than 4 hours for me to do it all on my Corolla. It will be hard for you and your shop to get to the bottom of this until more tests are done.

54

Yeah, you’re right. It just sounded like a lot when you were describing it. But if it only took you 4 hours to do all that, then, yeah, it’d probably take a mechanic no more than an hour or two, so that sounds good. I’ll definitely share your notes with my mechanic next time I speak with him about the problem (waiting to accumulate more data first).

BTW, after the other day when the “clunking” sound came back for the second time and there was no hesitation problem, the car’s been fine. No clunking, no hesitation/lunging. So it comes and goes, apparently. I’m guessing it’ll be back in a few days.

BTW, did you have a chance to watch that brief video I linked to in my last message? Does that sound like anything you recognize? Does it sound like perhaps it could be the throttle body making that noise?

Thanks!

55

Update re. clanking sound. Car in gear (Reverse or Drive), A/C on, car made sound.

Put car in Park. Sound went away.

Put car back in gear (holding brake pedal down), sound returned.

Turned off A/C. Sound went away.

Turned A/C back on. Sound returned.

So only when it’s in gear AND the A/C is on does it happen. And it doesn’t happen all the time, even with that. Usually only when I start driving, then goes away. And this is only the third time it’s happened.

56

AC on vs AC off, or Drive vs Park, both put more mechanical load on the crankshaft and torque converter. AC on puts more mechanical load on that accessory belt, which might point to a problem w/something on that belt path; but I don’t see how D vs P would put more load on that belt. I’d guess you are looking at an internal engine problem, a torque converter problem, or engine/transmission mounts.

57

Could any of those things also cause the hesitation/lunge issue or the sudden deceleration issue? Just trying to see if these are related or if they’re completely separate issues that are happening around the same time.

Thanks.

58

Update/Correction. I previously said that the knocking sound didn’t happen in Park. I listened again today, and it does happen it park, but it’s much quieter. Gets louder when the car is in gear.But still completely goes away when A/C is off.

Also, it only lasts a few minutes at most when I start using the car. After that, with A/C on or A/C off, engine sounds normal. But for first few minutes, if A/C is on, there’s a knocking sound, as per the 6-second video I linked to in message #52.

Thanks.

EDIT: Forgot to note: since the knocking sound was happening in Park, I was able to pop the hood and get a closer look. It’s definitely coming from inside the intake manifold (the large block that says “3.3L V6” on top of it).