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Erratic tachometer and engine running up while accelerating

 
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macleod348
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PostPosted: Thu Dec 16, 2010 5:38 pm    Post subject:  Erratic tachometer and engine running up while accelerating Reply with quote

Hi all,

First time visitor to the site and it seems this may be the place to find the answer to my problem.

When I accelerate moderately, i.e. out of a school zone, from 55 to 65 on the interstate my tach jumps all over the place. For example if I am cruising at 1200 rpms when I press on the accelerator it will jump to 1600, then settle at 1300, then jump to 1700 and settle back to 1400, 1800 then 1500, etc until it gets to where it needs to be to maintain speed. I can hear the engine come up and something "grinding" down near my feet. From time to time there is some hesitation when I try to accelerate like the car doesn't have any power. Also if I push the pedal down further it will jump to overdrive and take off without issue.

The tranny was rebuilt in March of this year after experiencing the hard shifting that is so common in these cars, so my first thought was that being the issue again. I took it back to the shop and they couldn't find anything wrong with it. They put a code reader on it and got a thermostat code off of it but nothing else. Their suggestion was that the top radiator hose was somewhat flat so I needed to replace that and the thermostat. The hose has returned to it's normal shape since then. I think it only appeared flattened due to having replace the air filter the day before and I most likely leaned on it in the process. They told me the thermostat has some control over the torque converter, this seems suspect to me.

I have tried a couple of bottles of fuel system cleaner with no change, and just tried a topical application of throttle body cleaner with no improvement. I may try pulling the throttle body on Sunday when I am back at the firehouse again.

Plugs and wires were replaced over the summer and were gapped correctly.

Any help you guys could provide would be greatly appreciated.
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shagnwagon
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2000 Chevrolet Impala


PostPosted: Thu Dec 16, 2010 6:41 pm    Post subject:   Reply with quote

What plugs and wires did you go with?
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macleod348
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PostPosted: Thu Dec 16, 2010 7:11 pm    Post subject:   Reply with quote

They are Delco plugs and I am not sure of the wires. They came from Advance Auto. I started out with Autolite plugs, I think, but ended up with one of them being cracked so they replaced all of them with Delco's. Of course the one that needed replaced was #4, the most convenient to get to.

I can confirm also that the wires are placed correctly. I did them one at a time to make sure I didn't cross any.

The rough acceleration was present prior to the plug change, I was hoping they were the problem.

I guess I should have mentioned earlier that my car is a 2005 LS with the 3.8L V6.
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macleod348
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PostPosted: Sun Dec 19, 2010 6:47 pm    Post subject:   Reply with quote

Check engine light came on while on my way home from the firehouse Friday morning. I stopped in and had a code reader put on with a P0128 code for the thermostat. I changed it and the top hose out today with positive results on how quickly the car reached operating temperature.

While I was in the area I went ahead and took the throttle body apart and cleaned it out. Took it out on a test drive to check for leaks on the hose and thermostat. No change was noticed in the original problem.

Any ideas?
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bbengineer
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1998 Chevrolet Corvette
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PostPosted: Sun Dec 19, 2010 8:55 pm    Post subject:   Reply with quote

Even without a code, it sounds like the tranny is acting up... I would take them for a drive and show them what it is doing

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macleod348
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PostPosted: Sun Dec 19, 2010 9:40 pm    Post subject:   Reply with quote

Thanks, that is what I have been saying. I will be taking it back over to them tomorrow morning after I get out of the firehouse. I'm sure they'll be impressed with the dash being torn apart. There is a horrible squeak somewhere inside the dash on the driver's side that I am going to have to locate before I lose my mind.
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macleod348
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PostPosted: Sat Jan 08, 2011 3:31 pm    Post subject:   Reply with quote

Transmission rebuilt last week. Now we are back to hard shifting from a start though. Getting really tired of not having a car because of a junk transmission.
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00impala123
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PostPosted: Sat Jan 08, 2011 7:22 pm    Post subject:   Reply with quote

macleod348 wrote:
Transmission rebuilt last week. Now we are back to hard shifting from a start though. Getting really tired of not having a car because of a junk transmission.


do yourself a favor and get a built transmission (TEP, or there is a guy on clubgp.com that builds them) (or get a dealership one with a warranty)

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macleod348
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PostPosted: Tue Jan 18, 2011 9:47 pm    Post subject:   Reply with quote

Well....... Hard shifting was supposedly fixed. They claimed to have found a leaking axle seal, causing a tranny fluid leak? Picked it up last night and drove it home without issue. Driving to the firehouse this morning I felt it do the hard shift again, just not quite as severe. I just went out and drove again for a few minutes since we have full staffing and it did it at least twice while I was out. Back to AAMCO again tomorrow morning, this stuff is getting really old. Unfortunately when I had the work done back in March I bought the lifetime warranty so I am kind of stuck going to them until the end of time.

To top it all off I think I have a wheel speed sensor going out too. ABS keep trying to kick on when braking at low speeds on dry pavement, then the "Service Traction System" light comes on as well as the Trac off and ABS lights. Unless of course this is somehow tied to the transmission.

Pretty well fed up with this whole car right now.
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