Car has rough idle, especially in Drive/Reverse. What's wrong?

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Car has rough idle, especially in Drive/Reverse. What's wrong?

Postby peirce » Tue Oct 04, 2011 9:20 am

I just recently bought a used 86.5 Toyota Supra (super cheap, super-good cosmetic condition), and it seems to have an issue. The car rumbles at a stop. Shifting into Neutral lessens the problem considerably, but does not entirely diminish it. Power does drop as well while it does this. The car is (obviously) old and does have quite a few miles, but the car was serviced, maintained, and garage-kept, so I'm hoping it's not a serious, need-to-replace-your-engine kind of problem.

I've heard that it could be the exhaust or possibly the ignition, but I honestly don't know myself. I have access to a shop with a lift, so with the right direction, I'll be able to fix something relatively simple.

Thanks for any help!
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Car has rough idle, especially in Drive/Reverse. What's wrong?

Postby anwyll » Tue Oct 04, 2011 9:23 am

Could be something as simple as spark plugs / distributor cap. Though exhaust (mainly catalytic converter) can rumble at idle - this would usually dissipate upon acceleration.
Worst case would be bad timing, or piston misfire.
This is something that a qualified, or experienced mechanic would just need to drive around for a minute to diagnose. I know my answer doesnt fix anything, but someone driving first hand would be able to figure it out rather quickly I think.
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Car has rough idle, especially in Drive/Reverse. What's wrong?

Postby llawr » Tue Oct 04, 2011 9:24 am

If your have an older car and it seems to have been taken care of, but it does not run right, there are several things you can do to check over the vehicle and see what can be done, without spending a lot of money. First, it could be something as simple as your transmission fluid is low, or your transmission fluid and filter needs to be changed. Second, have the compression checked on each of the cylinders. The technician should be able to advise you if it is within acceptable levels, generally you want the psi to be close to each other, but not more than 15 psi. Third. If it is old, it is likely that the spark plugs have not been replaced, or the distributor cap and rotor. If the car is new enough and does not use a distributor, then the fuel injectors may be dirty and adding an injector cleaner to the fuel may help clean them out. The shaking could also mean your timing is off a little bit. It could also mean your spark plugs are not firing correctly and you need to replace the spark plug wires too. These are repairs and checks that you can do yourself, which would be fairly simple to do. If your car has white smoke out the back while driving, it can be much more serious. It can mean your engine needs a new head gasket, or intake manifold gasket. Hopefully this will head you in the right direction. Good luck.
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Car has rough idle, especially in Drive/Reverse. What's wrong?

Postby pimne » Tue Oct 04, 2011 9:32 am

Check your engine mounts
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Car has rough idle, especially in Drive/Reverse. What's wrong?

Postby maelisa89 » Tue Oct 04, 2011 9:39 am

Here are a couple of easy fixes that you can try yourself.

You won't even need access to a lift to take care of these items.

I like to try the least expensive fixes first:

Check out your Exhaust Gas Recirculation (EGR) and Positive Crankcase Ventilation (PCV) valves.

This may help, but if not, at least you haven't spent any money and have eliminated two potential causes of your problem.

See links below for detailed information:
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