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I have a '93 Acura Integra with automatic transmission. Ever since I got it some time ago the car has been vibrating a lot when stopped at a light, for example. The vibration is worse when in gear than in neutral, but it's present in both cases and slowly goes away as I drive and get closer to 2k rpm --- car idles close to 1k rpm. Also the problem is worse with a warm engine/transmission than when it is cold, presumably because at higher temperatures it idles at lower rpm.

Now, I noticed recently that the engine mounts were bad, so I replaced them. This only made the problem worse. Someone suggested I try injector cleaning fluid and that seemed to have made a difference, but only until I was done with that one tank of gas.

What could cause this behavior? Should I check the fuel filter or the injection system? Could this be a problem with the transmission and if so, what exactly could be going wrong?

[Edit] At some point when I was doing front axle work (one of the CV joints needed replaced, probably went bad due to the broken mounts) I noticed that there is some decent play in the differential. I understand some play is normal, but I'm also noticing sometimes, after I turn off the engine and release the brake the car will "shift" a few inches forward or backward before settling. Could this be related to the vibration?

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4 Answers

Sounds like the Idle Air Control Valve and the Intake Manifold must be removed and cleaned.

The vibration is worse when in gear than in neutral

In gear there is a much greater load on the engine. Power is being transfered to the transmission and then to the wheels. This is going to cause the idle to drop a bit and this is where you'd feel the most vibration.

Also the problem is worse with a warm engine/transmission than when it is cold

When the engine is cold, the Air/Fuel mixture is set (by the ecu) to a rather rich condition. Giving you a higher idle while the engine control systems are helping the vehicle obtain operating temperature. When the vehicle is hot (operating temp) the mixture is greatly reduced, bringing it back to where it should be, causing the idle to drop and making the vibration much more noticable.

For the project you will need a few cans of carbuerator cleaner (three, maybe four) and a wiRemove the intake manifold and wire brush (one of the flexible ones that resemble a pipe cleaner). Remove the intake manifold and spray the inside and work the brush down each runner until the carb cleaner comes out clean(ish).

In the process of removing the intake manifold you will most likely end up breaking a few things like your PCV valve so you might want to pick one of these up as well while you're at the store grabbing supplies. Also, be sure to clean the Idle Air Control (IAC) while you have everything exposed.

NOTE: This repair is going to take some time and is only going to come out as good as you want it to. So please make sure you have a day where you can really tear into it. I promise you wont regret it.

As far as replacing the mounts goes. There are a ton of other symptoms other than vibration that come with broken motor/transmission mounts. Since I've never driven your car I can't really say if I would have even considered replacing them to solve the issue.

Also, please take note that you are driving an Inline 4. These motors are known to be rattle boxes. They put out a much greater / less smooth feeling than any V-style motor built.

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Thanks for the thorough answer. My gut tells me that everything you say is correct and this is what I must do. The loose motor mounts were grinding down one of my CV joints so I had to replace both those things regardless of the current rattle. –  vlsd May 1 '13 at 16:00
    
I did this except I only removed the throttle head and all the other valves and cleaned them. I didn't take out the whole intake manifold as that would have required draining my coolant and a lot more time than I had. Anyway, this cleaning and spraying carb cleaner straight into the intake manifold did not have any effect on the vibration, which makes me think this is the wrong path. –  vlsd May 4 '13 at 23:20
    
was the idle air control valve cleaned? and PCV valve cleaned / Replaced? The Idle Air Control Valve when removed will spill coolant it's located on the back side of the intake manifold and has a few 12mm bolts holding it on. P.S. spraying carb cleaner direclty into the intake is not the same as removing it and cleaning it. –  cinelli Jun 2 '13 at 8:06
    
Yes I removed and thoroughly cleaned both those valves. I did not remove the whole intake manifold as the space is rather tight, there are a lot of things in the way and it would require me to drain and replace the coolant, something I wasn't prepared to do just yet. The problem could still be somewhere down in the intake and/or one of the injectors. –  vlsd Jun 3 '13 at 16:58
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Based on your information, it appears your transmission is on it's way out. If your mounts were bad and the car was driven for a lengthy period of time, you were putting more stress on the tranny than usual. Being a FWD car with the tranny on the side, Horizontally opposed to the engine, it's verifiable when you say the car "shifts" when turning it off. This tells me that your torque converter is not fully releasing or your tranny gears/valves/springs are going if not bad already. I would drain the tranny fluid looking for metal debris and such, this will tell you that the tranny is grinding internally, not good. Or new fluid might lessen the effect, thus confirming it's your transmission. Moving on to the motor, if you're not seeing any smoke, white or black, your motor is probably fine. But still closely inspect your crank pulley as *This crankshaft is externally balanced by that pully.

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I did change the tranny fluid not long ago and there wasn't any sign of metal shavings or anything else. New fluid also didn't impact the effect. I'll check the pulley, thanks! –  vlsd Apr 30 '13 at 16:32
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I want to add also look at your ignition coil for cracking. Stumbling could be your coil arcing to the block. This would explain it getting worse as the motor heats up. –  Terrence LP May 1 '13 at 13:56
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If "injector cleaning" products helped but only lasted for one tank, I would try spraying Seafoam directly in at the throttle plate rather than putting an additive in your fuel. This should be a lot more effective at cleaning the injectors.

If that doesn't help, my best guess would be that the vibration is from unequal power from one or more of the cylinders for a reason other than the injector. A compression test would be the natural first step for checking this possibility, It's also possible that you have inconsistent belt tension as the engine rotates due to a bad idler pulley or bad bearings in the water pump, alternator, AC compressor, power steering pump, etc.

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Great suggestions! I will try the seafoam shortly and come back with results. If it is a pulley or bad bearings (the car is pretty old, bad bearings everywhere) how would I check that? –  vlsd Apr 29 '13 at 15:12
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The most reliable way is probably to take the belts off and try to rock the pulley side-to-side and up/down and see if it has any play in it. But for stuff on the timing belt that may be more work than you want to do if you don't have a good reason to believe it's the problem. You can probably get a good idea if the pulley is wobbling just by watching it move with the engine running. –  R.. Apr 29 '13 at 15:29
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By the way, before you put any more effort into checking the pulleys than some casual inspection, you should probably do the compression test first, at least as long as the spark plugs are easily accessible. Unfortunately that's probably more likely to be the source of the problem. But yes, do the seafoam first, because it's easy and lots of the time it fixes what's wrong. :-) –  R.. Apr 29 '13 at 15:32
    
Seafoam didn't make a dent. Compression test is next. –  vlsd May 4 '13 at 23:21
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You replaced the engine mounts? I would guess that since you had to change the engine mounts that there is a good chance that the tranny mounts may need to be changed as well...what is the drivetrain assembly like in that car since it is fwd, sometimes if the driveshaft in a rwd car is unbalanced it will cause the car to shake

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by motor mounts i meant all four mounts that keep the engine and the transmission in place, so including the transmission mount. yeah, the car is fwd and the engine/transmission are mounted parallel to the axle. –  vlsd Oct 6 '12 at 18:14
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