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Second Generation Legend (1991-1995)

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Old 01-25-09, 05:52 PM   #1 (permalink)
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Roughness accelerating at low RPM

So I was out last night and my car started acting up. The first thing I noticed was that the car was shaking noticeably when it was idling at 650 RPM, but that seems to have disappeared. Since then trying to accelerate at low engine speed (~1500-2200 RPM) causes a fairly violent shuddering. A bit higher and it actually becomes a periodic shudder, it'll be fine for a second then shudder for a second. As the engine speed increases it feels more like a brief, intermittent, slip or miss (2500-3000 RPM) and at high RPM it seems fine. As an example, going 55 mph in 6th and stepping on the gas it shudders like crazy, dropping into 3rd and and stepping on the gas and it flies without issue. Seems to rev up normally in neutral or with the clutch disengaged.

My first thought while it was shaking at idle was that it felt like when the harmonic balancer went in my Camaro, but that was a long time ago and I don't really remember exactly how that behaved. Anyone had that problem in their Legend? I don't know what a broken motor mount would feel like, but I suspect it could be similar as well.

When the shuddering started I immediately though about axles, but it seems to be an engine speed thing. I haven't noticed and grinding noises or anything, and I'm not noticing any disparity between engine speed and car speed that would indicate slipping in the drivetrain.

About the only other thing out of the ordinary is that my idle seems slightly low (went down to just over 600, 700-750 is normal for me), and maybe a bit rougher than usual (it could just be that I'm listening more closely than usual).

Besides playing around on the drive I haven't done any checking yet. It's bloody cold outside and the garage space I usually work in is currently occupied. If anyone's had any similar symptoms, suggestions for what to check, or general questions, fire away. I've given a few of my thoughts, but I haven't actually ruled anything out.
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Old 01-25-09, 11:53 PM   #2 (permalink)
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Forgot to mention:
1. there's no check lights coming on
2. this (in case it wasn't obvious from the description) isn't the usual 1500 RPM shudder.
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Old 01-26-09, 09:43 AM   #3 (permalink)
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I had similiar problem per your description. after researching and a reply from a forum member we figure it was the TPS/TAS. Hopefully it's the same issue with your's...
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Old 01-26-09, 11:54 AM   #4 (permalink)
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My GS never threw a CEL code with the TPS/TAS issue? I dont think it throws a code though. Just from my experience fixing the TPS/TAs issue...

Ha I guess if it gets bad enuff it will throw a code, my bad:

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Old 01-26-09, 12:10 PM   #5 (permalink)
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Quote:
Originally Posted by NEOKEN View Post
Based upon your brief description there is a possibility it could be the motor mounts.
However I must ask Is your tune-up maitenance up to date?
Plugs, etc? Could it be a bad coil pack?
Its difficult for me to say for sure without me actually looking at your car.
By the way, you can adjust the idle up or down by turning the adjuster screw at the top of the throttle body if neccesary.
Thanks for the response, I appreciate that it's nearly impossible to diagnose something over the internet like this.

The plugs will be the first thing I check when I get a chance, and I'll change them while I'm at it (since I haven't bothered to do that yet). I'll also go through and see if pulling off coil packs indicates a spark problem on any cylinder. I'd expect bad plugs or coils to be causing me problems at idle and higher RPM as well, but I'll gladly defer to anyone who knows better than I do (which is pretty much everyone ).

Other maintenance items: oil, trans fluid, diff fluid, and coolant are all good. Injectors have probably never been cleaned (certainly not since I got the car). I've never checked the fuel filter. The air filter looked good when I last checked it, that was a few weeks back (I'll give it another check or change it out anyway though). I've never checked fuel pressure, compression, or vacuum (I think a vacuum leak sounds pretty reasonable for my symptoms as well).

I'm not going to worry about the idle speed yet, it's usually spot on and it was only a few RPM low. I just mentioned it in case it might seem relevant to anyone who's had a similar problem.

Thanks again for the response. It does feel more to me like a fuel-air-spark problem than vibration problem, but I don't have nearly enough experience to be sure about that feeling. Looking around at crankshaft pulley posts it doesn't seem like there's any step in between intact pulley and broken pulley.
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Old 01-26-09, 12:14 PM   #6 (permalink)
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Quote:
Originally Posted by Old School View Post
I had similiar problem per your description. after researching and a reply from a forum member we figure it was the TPS/TAS. Hopefully it's the same issue with your's...
Hadn't even considered the TPS, though now that you mention it I think I remember reading that thread. Should be easy to check too

Thanks.
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Old 01-26-09, 07:29 PM   #7 (permalink)
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That really sounds like a spark plug or coil pack issue I would start there its a pretty cheap fix.
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Old 01-28-09, 01:10 AM   #8 (permalink)
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Haven't had a chance to check anything yet, but I did get behind the wheel again and found out that there's no issue when I'm running cold, only starts once it warms up.
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Old 01-30-09, 12:11 PM   #9 (permalink)
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Quote:
Originally Posted by NEOKEN View Post
However I must ask Is your tune-up maitenance up to date?
Plugs, etc? Could it be a bad coil pack?
Quote:
Originally Posted by White_russian5 View Post
That really sounds like a spark plug or coil pack issue I would start there its a pretty cheap fix.
Finally got some time and enough warm weather to change plugs last night, and it drove fine on the way home last night as well as to work this morning Thanks guys.
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Old 01-30-09, 03:06 PM   #10 (permalink)
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Working this same issue on mine now. It shakes the steering wheel while driving but now idles rough sitting still. It is definitely the engine and not mounts or suspension. All ignition and fuel mechanicals checked good. I'm now checking the MAP sensor and ECM route. Will post when I finish.
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Old 01-30-09, 03:28 PM   #11 (permalink)
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Quote:
Originally Posted by Djets View Post
Working this same issue on mine now. It shakes the steering wheel while driving but now idles rough sitting still. It is definitely the engine and not mounts or suspension. All ignition and fuel mechanicals checked good. I'm now checking the MAP sensor and ECM route. Will post when I finish.
My steering wheel didn't really shake at all with the bad plug(s), and the idle was fairly smooth. Good luck!
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Old 01-30-09, 06:50 PM   #12 (permalink)
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Quote:
Originally Posted by Djets View Post
Working this same issue on mine now. It shakes the steering wheel while driving but now idles rough sitting still. It is definitely the engine and not mounts or suspension. All ignition and fuel mechanicals checked good. I'm now checking the MAP sensor and ECM route. Will post when I finish.
Totally different issue if its coming through your steering wheel.
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Old 03-04-09, 11:19 PM   #13 (permalink)
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i'm having a similar problem, its intermittent, but after driving for a while it will start getting rough around 2500rpm
and if i lightly push on the gas past 2500rpm nothing will happen for a second until i push it far enough,
then it will accelerate, usually with a kick down to 3rd... if i cruise long enough in the rough zone the CEL will come on.
(44 - right fuel supply) and as soon as the light comes on, the problem goes away.
so i'm guessing it's some kinda sensor where the ecu switches to failsafe values??
i think im gonna check the tps next or O2 sensor
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Old 03-04-09, 11:24 PM   #14 (permalink)
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Quote:
Originally Posted by HeyChef View Post
i'm having a similar problem, its intermittent, but after driving for a while it will start getting rough around 2500rpm
and if i lightly push on the gas past 2500rpm nothing will happen for a second until i push it far enough,
then it will accelerate, usually with a kick down to 3rd... if i cruise long enough in the rough zone the CEL will come on.
(44 - right fuel supply) and as soon as the light comes on, the problem goes away.
so i'm guessing it's some kinda sensor where the ecu switches to failsafe values??
i think im gonna check the tps next or O2 sensor
Just based on the "Right Fuel Supply" description I'd change the fuel filter and check the injectors, maybe the fuel pressure regulator (now idea how to check the injectors or the FPR, but it's how I think I'd proceed). I don't think either the TPS or O2 sensor would throw a code for the fuel supply (honestly I didn't even realize there were fuel supply codes).

This problem sounds different from the one I had, in that mine got better above 2500 RPM.
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Old 03-11-09, 04:46 AM   #15 (permalink)
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Quote:
Originally Posted by sap View Post
Finally got some time and enough warm weather to change plugs last night, and it drove fine on the way home last night as well as to work this morning Thanks guys.
your prob is the only one that bugs me on mine...

it revs the same way, and bogs on low end. but you dont' have a kickdown cable. i was guessing towards whatever mechanism keeps the car from stalling while at a red light on the brake, in gear; someone else told me try changing the plugs...

i've got to, cuz lol.. i sanded my plugs a month ago, and they came with the car. ;]

but i'm still really interested in what keeps an auto car from stalling at a red light.....
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