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Old 03-19-2012, 05:17 AM   #1 (permalink)
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2003 3.4 - Starting / Running issues at full temp

I have two strange problems that I couldn't seem to find a thread for, if there is one let me know. Two weird things, I believe they're distinct, maybe related, but here goes.

2003 3.4 L base model, 182000 miles. No CEL.

1) At full temp (~ 195 degrees), after driving for a while, if I am coasting and I lightly press the accelerator, the car jerks a little back and forth. It doesn't make a clunking noise like the half shafts are going, and the engine doesn't sound weird. If I press the throttle a little more, the jerkiness goes away. Other than that, the car shifts perfectly fine. At first I thought maybe the trans is going, but intuition tells me it's an engine problem. Could it be a sensor? Any thoughts? This happened before and after putting a new thermostat in.

2) A week or so ago, I had to replace the fuel pressure regulator, because the factory one started to leak. I replaced it, for a couple of days, no issues. Now, once in a while, if I drive the car for some time, let it sit for maybe 15-20 minutes, then go to start it again, it wants to die unless I give it gas. Once it starts running, no issues, and the fuel pump sounds fine. In the past, I've never seen this problem related to the fuel pressure regulator unless it was a cold start, but it seems to only happen when it's warm.
This did not happen prior to installing the new regulator. Could the new regulator be defective (cheap Made in Mexico Autozone version).

Thanks, everyone.


Last edited by jrd0304; 03-19-2012 at 05:26 AM..
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Old 03-25-2012, 04:21 PM   #2 (permalink)
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Similar Issues Need Help Too.

My Wife's car is having similar issues you describe. When the car is running and you either set the cruise or maintain speed at 54+ mph (even at 80 mph) the car experiences the same issues as you describe. When accelerating or coasting the car is fine. Cruising at 50 mph is no problem.

Any ideas?

Car: 2001 Impala, 3.4L, 145,000 miles. No other major issues with the car.

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Old 03-26-2012, 10:23 AM   #3 (permalink)
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could be defective..have you changed the fuel filter, I would try that first.

also..the jerking could be motor mounts, dogbones, etc.
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Old 03-27-2012, 05:26 AM   #4 (permalink)
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@leaux - In my case, the car jerks when I'm coasting, and then I lightly tap the gas pedal. If accelerating with a normal amount of pedal, the car doesn't jerk/hesitate. I'm going to guess it is possible we may have the same problem. I have the issue at all speeds, from 25MPH all the way up to highway speeds of 65MPH+. I've searched around and I haven't really been able to find any leads on why this could be happening, since it could be caused by virtually anything.

@00impala123 - Possibly, I'll see if any of the mounting brackets / grommets look weak / rusted /etc.

It's almost as if it wants to downshift or something, but it's caught in between the cruising gear and the lower gear, and it can't decide which way to go.

I added a bottle of Lucas to the fuel and I haven't had any issues starting the car since then, at least, so that problem hopefully stays away.

But the jerking thing is weird. I'll be cruising at about 35 MPH, and then lightly tap the accelerator to maintain a constant speed, and then it begins to slightly jerk back and forth. Maybe the kickdown on the transmission is messed up or something, but if I give it a little more throttle, the jerking disappears. I'm not getting a CEL either. Maybe the CAT is clogged? It's perfectly driveable other than that, but if I want to sell it to someone, I'd probably want to get this taken care of first.


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Old 03-27-2012, 06:51 AM   #5 (permalink)
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Light throttle/low load miss

Have you changed your plugs/wires ?

If you have, then may be a coil pack starting to die


That's what it sounds like to me.

Paul

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Old 03-27-2012, 04:55 PM   #6 (permalink)
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Quote:
Originally Posted by retiredpauly View Post
Light throttle/low load miss

Have you changed your plugs/wires ?

If you have, then may be a coil pack starting to die


That's what it sounds like to me.

Paul
Yeah, but normally a bad plug or wire or coil pack will cause a misfire which will cause a check engine light.

I have experienced some jerking when dealing with cars that had a clogged or bad converter. You can check the pressure coming out of the tailpipe. Normally with a bad cat your temperature will increase and your top speed will decrease. It will take you longer to get up to speed and the top speed will be limited. The jerking from a bad cat will normally occur at take off. At least that is what I have experienced in the past.

I think it is either a fuel delivery problem or the transmission.
I would not rule out anything yet until doing complete checks.

Unplug the EGR valve. Your check engine light will come on. Then drive the car and see if the jerking is any different, meaning better. If it is with the EGR unplugged then your cat is probably bad.

I had a car with a bad MAF that would not start unless I gave it a little gas and would die at stops unless I kept my foot in it a little. That car was had numerous problems though...

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Old 03-30-2012, 08:38 AM   #7 (permalink)
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Yes, I haven't gotten any CEL's from a misfire/coilback, so hopefully it's not those. I'll try unplugging the EGR and see if it goes away. It only seems to do it when the car is running at full temp, and on some trips, it doesn't do it at all! Oh well, I'll give it a shot, thanks again, everyone.

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Old 04-02-2012, 05:31 PM   #8 (permalink)
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One of my spark plug wires came out of the boot, so I pushed it back in. I'm wondering if this is causing it. I'm going to replace the wire and see if that does it.

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Old 04-02-2012, 06:03 PM   #9 (permalink)
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Normally if the plug wire comes off or is bad then it will trigger a misfire and will cause a check engine light. I had a plug wire do that once when it got corroded inside and wasn't making the connection right.

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Old 04-04-2012, 09:58 AM   #10 (permalink)
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I did see some other models had similar issues due to coil pack/plugs/wires, so maybe this is similar. Two of my wires I know were bad because the part that clips onto the plug had separated from the boot - So I replaced those two wires, and while doing that, I also noticed one of my upper intake bolts was loose, how that happened, I have no clue. I agree if there was a misfire, why no CEL? I'm grasping at straws at this point.

So.. After the wires, I tightened the loose UIM bolt down, and took it for a quick spin, no jerking yet (It did jerk on my trip back and forth to the parts store, but not after I replaced the two wires and tightened the bolt). I'll keep my fingers crossed.

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Old 04-08-2012, 01:49 PM   #11 (permalink)
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Blah - That didn't do it. Next thing I'm going to try is disconnecting the battery for 24 hours to reset the computer. Beginning to think the transmission is shot.

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Old 04-08-2012, 03:32 PM   #12 (permalink)
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I bet bad coil or,,,,,,,,,,,,

Perhaps the converter lock up switch ???

Maybe??

RPM bouncing at all ?

ECM will re-set after about 5 mins I think on a battery disconnect


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Old 04-12-2012, 01:29 PM   #13 (permalink)
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On the datastream, I could see the RPMs moving, but not at an extreme rate. Would a bad coil throw a code, or is it possible that a coil could be bad, but still not throw a code?

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Old 04-12-2012, 02:58 PM   #14 (permalink)
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It is possible that it won't, but normally you would see a misfire code.

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Old 08-09-2012, 05:30 PM   #15 (permalink)
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Changed plugs, runs better, but still happening. Two tanks with seafoam - still happening. Changed all three coils with new AC Delcos tonight - let's see if this works. If it does I'll let you guys know.

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