Why does my car shake when I first turn it on?

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Why does my car shake when I first turn it on? This first happened last night. Today after work i started up my car and it did it again. The car only shakes when its been off for more than 8 hours. There are no check engine lights. All fluid levels are always full. I think it might be a misfire or something with the transmission.
 
Not sure how aggressive your driving style is but if you ever floor the car and let it wind up (warmed up of course) you would find out if it is the plug wires. If the wires are bad it will usually misfire when you really lay into it. Another thing to check is to see if you are having the LIM leaks. Also check your oil to see if any water is mixing in with it.
 
The idle speed must be too slow when the engine first starts. Do you know of a mechanic who is good at tracing electrical, wiring, sensor problems?
 
The car only shakes for about 15 long seconds. It continues to shake when I put it from park to reverse. I don't think it's a motor mount because when I put it from drive to park, everything works fine. I think the intake gasket is leaking. You can see oil around the outside of the engine. I change the oil every 3,000 miles. I don't see coolant in it.
 
You might check that you are not losing coolant. It might be pooling in a cylinder and cause a misfire until it is burnt out.
This is the exact same thing I dealt with on the 3400 in the Montana after I did the LIM on it. Start it and it would miss like it had a dead hole for 10-15 seconds. Never caused a CEL for misfire, just a "EGR Stuck" code. After that it was smooth as new. Kinda thought that might have been it from the extra 'air' coming through the EGR. I had done the ignition with the LIM so that was all new. Compression was within tolerance. Actually, all the cylinders were really close to each other.
In the mean time I had the oil tested again and it had twice the coolant intrusion than the test that made me do the LIM. In half the miles.
btw, I never saw coolant in the oil either. Since I had been testing oil that is how I caught it.
Something else I noticed got me suspicious. The coolant smelled like gas. It was pretty potent. It had also changed color from [censored] yellow to a kind of burnt orange color.
Finally I threw my hands up and bought a combustion gas detector setup that you put on the radiator. Popped positive for combustion leak almost instantly.
When I finally pulled the rear head, I seen what was going on. The gasket material had been eaten starting at a coolant port and once it got to the fire ring of the back passenger hole it rusted that out. Over a period of time after shutoff due to the pressure in the coolant system it was seeping into the cylinder and pooling. Causing a misfire at initial startup. Still dont know how it passed a compression test so well. That whole setup made me question the validity of compression test results as manner of grading an engine. They only seem to show obvious defects as a sort of "Go/No Go" system. More like "Maybe Go/No Go." :p
Didnt mean to write a book, or to scare you unnecessarily. Just wanted to explain my experience. :p Sorry.
 
Before we start condemning the intake and/or head gaskets, lets start a little more simple. When was the last time it was tuned up? Fuel filer, air filter, plugs, wires, pcv valve and so on? Vacuum leaks?

If you see oil at the base of the LIM, then no doubt it's starting to leak (doesn't necessarily mean coolant just yet), but for now start with the basics.
 
The fuel filter was replaced approximently 5 months ago, and the air filter was replaced 10 months ago. The mechanic told me that the spark plugs were fine. I personally checked the PCV valve by shaking it and it rattled. I changed the transmission fluid and filter about 2 months ago. I used Dexron III.
 
Only stone cold?
A coolant sensor that is faulty may be the deep down culprit.
It is telling the computer that the car is warm, when it really needs more fuel.
 
UPDATE: Ok I was driving to Dallas when all of the sudden the check engine light came on. 5 minutes later it started blinking so I turned around. I stopped by Auto Zone and it turned out to be a misfire. I breathed a sigh of relief. I thought it might be the transmission because I just changed it less than 10,000 miles ago. I'm going to take out the spark plug and see how it looks. I'm hoping there's no oil on it. If it looks kinda old, I'm going to change all of them with E3 spark plugs and Bosch wires. The service manual says to change the spark plugs every 30,000 miles. My car has over 170,000 miles and there's no telling when the spark plugs were last changed.

As for the coolant light, I'm thinking maybe a bad or dirty sensor.
 
Originally Posted By: johnsmellsalot
UPDATE: Ok I was driving to Dallas when all of the sudden the check engine light came on. 5 minutes later it started blinking so I turned around. I stopped by Auto Zone and it turned out to be a misfire. I breathed a sigh of relief. I thought it might be the transmission because I just changed it less than 10,000 miles ago. I'm going to take out the spark plug and see how it looks. I'm hoping there's no oil on it. If it looks kinda old, I'm going to change all of them with E3 spark plugs and Bosch wires. The service manual says to change the spark plugs every 30,000 miles. My car has over 170,000 miles and there's no telling when the spark plugs were last changed.

As for the coolant light, I'm thinking maybe a bad or dirty sensor.


Stick with an O.E.M. plug type.
 
Forget the E3s.

But an ignition misfire could be wire or coils , too.

And an ignition misfire would show up in normal driving, not just cold starts.
 
I concur with the plug recommendation. Go with the AC/Delco spark plugs, not the E3's. Advance Auto or AZ will have the newest rec. version of the correct plug for your car. I would use the AC/Delco wires as well. I know no one has mentioned, O2 sensors yet, but they are esp. critical to use the OEM O2 sensors for GM products.
 
I also agree - don't get the E3's. It's a gimmick plug, not even a platinum/iridium plug and they charge you like they are. I installed these in a 2002 Trans Am for a woman. She bought them at the advice of a parts man and I argued with her to let me replace the plugs with the AC Delco or even Autolights but she insisted. Two weeks later, she was back and told me to put whatever plugs I want in it.
 
The guy in Auto Zone also told me to stick with AC Delco. He said that the manufacturer spent millions designing the engine with those spark plugs. So I'm going to get AC Delco plugs and wires.

Someone else said something about the car only shaking on cold starts. The guy in Auto Zone explained this. He said he worked at an emission inspection place for 15 years. He looked at my spark plugs and immediately asked what brand of gas I was putting in it. I've been putting in Valero because its cheap and its on the way to work. He said only use gas that advertises detergents in it. An example of a gas with detergents would be Chevron with Techron. Anyways on the way to Dallas, the car started shaking really bad so I drove back going below 55 MPH. The car started misfiring while cold 2 days ago and then yesterday misfired from normal driving. That guy in Auto Zone sold me 2 containers of fuel system cleaner. He said it'd get that carbon out of there. I'm going to run 1 container after I fill up. I'll do this twice. After that, I'm going to change the spark plugs.
 
You are required to have detergents in any gasoline sold in the United States. Top Tier gas (Chevron/Shell/Mobil/Texaco etc) has more detergents but your car should be fine on any gasoline unless your car has other issues.

What it really sounds like is that your spark plugs became fouled and the parts store guy thinks it's due to the gasoline. Given the age of your car that might be true that deposits fouled the spark plugs but at the core the gasoline is not the cause. I would inspect items that control air/fuel mixture.

Here's a link to an article on EPA requirements for detergents: http://www.epa.gov/otaq/regs/fuels/additive/fact7gda.htm
 
If the car is shaking that badly, you are not running on all cylinders. First job would be to determine the culprit cylinder. You do that by running "cylinder balance" test. This is a fancy way of disabling one cylinder at a time and noticing *lack* of *worse* response. If you have coil for every cylinder, easiest is to disconnect the wires to each in succession.

Once you have found the bad cylinder, then you find if it is misfiring because of:-
1) No spark
2) No fuel
3) No air
4) or No compression
in that order.

You can either do this logically and methodically or you could start replacing the parts randomly. Something or other is bound to fix your problem!

- Vikas
 
Cylinder 1 is misfiring. I know this because that's when the engine code said when Auto Zone scanned it. No need to disconnect other cylinders. Another reason I don't think the system is too rich or too lean is because it would throw out a check engine code for that as well. I'm pretty sure it's a spark plug because the car ran like new the day before all this happened. Plus the spark plug was really dirty.
 
You should fix this as quickly as you can. A misfiring engine can destroy your catalytic converter in short order. Get the new OEM plugs and if the symptoms don't go away, get new wires or new coil for that plug depending upon your car.
 
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