: Engine Shaking

08-23-09, 08:52 PM
My P0300 (Misfire) code has went away but I still have a bit of shaking at idle (Park and Drive). Last night when stopped at 7-11 while my friend ran inside I decided to pop my hood with the engine running and I noticed my engine was shaking and is what is causing my car to shake since the way it shakes is the way the shaking feels.

Spark Plugs were replaced a while back with the correct A/C Delco's. I had ordered some wires from RockAuto but ended up returning them since my misfire went away.

My friend said its normal but I know when I first got the car it was so quiet and smooth that I couldn't even tell it was on.

What could be causing this?

08-23-09, 09:19 PM
Shaking is not normal. You should not even know it is running, nor should you have returned the wires.

08-23-09, 11:04 PM
I'll reorder them then...

What do you think could be causing it to shake? Motor mount?

The plugs should be the correct ones.

The reason for returning them went like this:

Tuesday got spark plugs changed but car still idled a bit rough

Thursday took it to the GM dealer for a ATF Exchange and Coolant Flush, got home and ordered the wires

Thursday picked up the car from the dealer and car ran amazing, I couldn't even tell it was on.

Finally got wires and shipped them back because I didn't seem to have the problem anymore...problem came back but I figured it was something else causing it like a dirty TB

I was going to go get a balance and hopefully alignment from Firestone tomorrow for $89.99 but that deal is good til Sept 12 so I guess I will wait and order the new wires.

08-23-09, 11:29 PM
I assume you are talking about an engine shake at idle. My guess would be a mild misfire. Maybe try misting the wires at night before reordering them. I know they are expensive, but being 10 yrs. old (if they are original) they are due.

08-23-09, 11:37 PM
Yes, it shakes at idle, Park and Drive.

Yeah, they were about $108 with Tax/S&H (RockAuto). I'm going to re-order them anyways, my mechanic said I most likely needed new ones since they are original.

08-24-09, 01:38 AM
Come to think of it, a better way to describe it is a shudder about every 2 seconds (give or take 1 second)

08-24-09, 09:27 AM
Could fuel be causing this? Moisture in the system or just a bum tank of fuel?
I'll get a bad tank of fuel in my Harley from time to time { it needs premium}. runs like Cr$% until I burn it out and get another tank.
my two cents..

08-24-09, 05:56 PM
My 94 Eldorado has these exact same symptoms.
Still working on a fix though. Plugs and wires were _NOT_ the fix.

08-24-09, 06:17 PM
IF we're all talking about a pre-2000 4.6 Northstar with 4 coils check your plug wires against the diagrams. Which wire is on which coil tower is critical, and if a pair of wires is connected to the wrong coil towers that will cause a nagging miss. Google "waste spark ignition" to find out why.

08-24-09, 06:46 PM
Thanks. I'll check it out Sub

I only use Shell V-Power, occasionally Chevron 91 Oct.

08-24-09, 07:00 PM
I tell you my 2000 STS has always had a slight "miss" during idle in the Park and Drive position since I bought it. I had it diagnosed sometime this year and it was said to be something to do with the 2000-2001 Northstar's having a cam issues that caused the car to have the miss. I did quite a few things to try to fix it, including new spark plugs, a new intake plenum, TB cleaning, etc. to no avail. Once i finally found out what it was, I just forgot about it. Never had a misfire code. Now that I think about it, the front coil pack is my bet because when I pressure wash the motor occasionally the car misfires like crazy.

I know this has nothing to do with your '99 N*, but your symptoms sound like mine.

08-24-09, 09:08 PM
Thanks for the info...

I did some checking best I could, didn't want to mess anything up and not have the car run for work tonight.

The wires look like they are in correct firing order. I was only able to about 80% of them since they were hard to pull on and I didn't want to disconnect anything.

Here's a pic and some videos.

Not sure what this is but it makes some sort of hissing noise (not sure how to describe it) and there is a bit of fluid on it:

The videos are of my car idling and starting up. The chime is loud in the 1st video but you can hear how loud the engine is from inside, may need to turn volume up though.



08-24-09, 09:50 PM
The big fuzzy pic :rolleyes: is the PCV valve and connector, which moves a LOT of air through the crankcase/cam cover areas to control vapor and condensation. There should be NO suction or hiss noise from there. If there is, suspect the 90 degree connector which joins the PCV valve itself with the vacuum pipe to the intake manifold.

You can find a new connector in the "Help!" blister pack rack at your local Pep Boys or Auto Zone store. DO NOT try to fix that vacuum leak with silicone or goop. Find a new connector.

08-25-09, 04:33 AM
easy fix? It pops on and off easily.

08-25-09, 01:22 PM
Too easy of a fix..

08-25-09, 02:39 PM
If the PCV valve itself rattles, it's good. You should only need the 90 degree connector - if the valve itself is gummed up,
a new one is about $1.75 at Pep Boys - look in the Fram catalog hanging on the PCV valve blister pack racks.

FWIW, that "rattle valve" has a calibrated tapered plug inside which is opened by engine vacuum,
allowing fresh air to flow into the (front ?) cam/valve cover, through the crankcase, and into the rear cam/valve cover,
purging moisture and vapor from the inside of the engine. Trace the vacuum system. Why a tapered plug ?
During an engine intake manifold backfire the plug slams shut, preventing flame travel to the crankcase.

08-26-09, 04:23 AM
So the connector which I took a picture of is the part that will most likely need to be replaced?

If it is bad what symptoms will I be having, if any?

As for the engine shaking could it be a belt? They were checked during both oil changes and said to be fine.

08-26-09, 05:30 AM
Also, mostly when the engine is COLD or cooling down the car will jerk when turned on.

I believe it does happen to sometimes when the engine is warm but not usually.

08-26-09, 10:12 AM
If the PCV connector is so loose as to cause a vacuum leak, that may well cause a rough idle due to a lean mixture.
If the PCV is clogged, that will cause a rough idle due to a rich mixture. Suss it out......

If the engine is visibly shaking, and you get clunks and jerks once in a while, I'd suspect a torn front engine mount.
Open the hood and start the engine. Now, watching the engine carefully, shift to D. Does the engine "rock" more than 1/2 - 3/4" ?
With your foot on the brake, rev the engine, in D, just a bit. Does the engine "rock" more that 3/4 - 1" ?? If so, motor mount.

08-26-09, 10:31 AM
I'll have to get a buddy later to help me with the shifting to D part and what not.

I've been guessing an engine mount.

Wouldn't I get a code if it was lean or rich?

08-26-09, 01:08 PM
You should get either a rich or lean code to go with the earlier P0300 code. But a code may not set always.

08-26-09, 08:32 PM
Look out for bad coils, but then acceleration will diminish as well and it won't be just at idle. Personally, just from what I've seen bad coils do, I would replace all four even if it's not yet necessary. I've seen cat converters glow red from bad coils. Considering how close the exhaust pipe is to the fuel tank, (especially on the old platform cars it runs right underneath) I am very nervous about overheating converters.

Like Ranger said, Replace the wires. And if you can manage, get the coils from Rockauto too.

Run some good highly concentrated injector cleaner through the system. I use RedLine, seems to actually make a difference.

If the miss doesn't go away with the new wires, check the plugs for any abnormal colors or build-up. Start disconnecting injectors one at a time while it's running. The one that doesn't make much of a difference when disconnected, will be the problem cylinder. Go from there. Check spark voltage at that cylinder, remove the injector and check for proper spray pattern (should be a fine mist from two super small holes, no streaming) and injector shut-off- you can do this by energizing the injector with 12 VDC and using compressed air. Carb cleaner will clean them out nicely, most of the time. Without voltage, if the injector still flows, toss that injector out and don't think twice about it.

-fuel pressure
-compression test.

08-27-09, 08:31 PM
So much work for this car, but I love the car.

I don't do any work myself, I'm not mechanically inclined.

I'll have the coils checked when I have the wires replaced.

Actually I do believe I did get a lean code before in Right & Left Bank but the code when away when I cleared it and never came back.