Sick of this problem... (Long)

[TachyonS14]

The problem goes like this. I start the car up cold, and there is little to no vibration. Car warms up and drives PERFECTLY for the first few mins. while the temp gauge is in the center. Then about 10 mins. of driving while in operating temperature, I get the vibration through the cabin and steering wheel while at idle and when I hit 2krpms on the dot, it rattles badly in my dash making my keys and everything make lots of noise. This continues till around 3krpms, then it slowly goes away with increasing rpms. My car idles at 650rpm and if i revv it to around 950-1000 no vibration. I mean I barely tap the throttle and it's gone, but not the rattles at 2krpms. This has been a problem since I’ve owned the car (over a year) and along the way I've done:

new spark plugs, plug wires, O2 sensor, cap and rotor, air filter, fuel filter, cleaned the throttle plate (which was very dirty btw) all new motor mounts (left, right, and transmission), I also ran Seafoam through the gas tank, crank case, and brake booster line.

After all that, I though I had narrowed my problem down to fuel since I have done almost everything concerning ignition/spark, and my engine was squeaky clean. So, I tested my fuel pressure to see if it somehow affected my problem. I tested it, and it was just fine, so that means my fuel regulator and fuel pump are getting enough pressure to push to the injectors.

My next logical step was to get new injectors despite that fact that I've already ran many different types of injector cleaners through. But, then It dawned on me that this problem kind of comes and goes which tells me that it is NOT a mechanical problem. I mean if it was a injector or something, It would do it all the time right?

So, what do you guys think I'm looking at? Clean maf? new maf? Coolant temp. sensor? This problem only happens under load, so it's not my suspension or stuff like that. For example, all this can happen while I'm not moving. When the car is in "vibrate/rattle" mode, even rolling up the windows causes fluctuations in rpm's (very slight, but still does it) and increased vibrations. I'm in need of

Hopefully this thread will help people from trouble shooting as much as I've had to if they have this same problem, or one like it.

[SilviaS14KA24DE]

timing belt? try changing that.

[[Zero-S]]

We don't use a timing belt...

[PapaSmurf2k3]

it could be something mechanical if it happens when the car is hot not cold, is the car a 5 speed or auto?, have you changed transmission/differential fluids lately? maybe its got something to do with a vaccum line that somehow only leaks when its hot. I doubt it could be MAF, but check the voltages if you want. possibly coolant temp sensor. are you using the correct oil weight? (5w30) try doing a compression check once the car starts doing it. thats all I can think of right now

[navysnail]

try bumping up the idle, its supposed to idle between 700-800 rpm

[[s3]]

1) Check for codes

2) Check your suspension

[TachyonS14]

Thanks for the input guys. The car is 5spd, and is running brand new transmission fluid and is running the correct oil weight in the engine. I have bumped up the idle a little with the screw, but it doesn't always stay there. For instance, if i have the a/c on it will idle at around 1k like it's supposed to. But sometimes it will idle at like 1200-1250. I will take your suggestion and check the voltage on the maf.

The viration is coming from the engine, thats a fact. I think that once my car gets warm, my maf sensor may be faulty and retarding the fuel mixture or something causing the engine to vibrate.

[TachyonS14]

1) Check for codes

2) Check your suspension

The car is throwing no codes because when I smogged it, they have to check for codes and if there were any, they would have failed me.

I do know that my current stock suspension is about to go out on me, and I plan to replace it anyway. But, the problem happens while I am parked, so could it still be the suspension?

[[s3]]

The car is throwing no codes because when I smogged it, they have to check for codes and if there were any, they would have failed me.

I do know that my current stock suspension is about to go out on me, and I plan to replace it anyway. But, the problem happens while I am parked, so could it still be the suspension?

Crapped out engine mounts will vibrate your car like making a milkshake.....just a thought.

[TachyonS14]

I've already replaced all three. I posted it above. It's not a huge problem, but it's really annoying!

[[s3]]

Must have missed that, check battery/alternator under load?

[TachyonS14]

Worth a shot.

[HaveBlue]

turn the car on, warm it up, and move the wires attached to the injectors. if the motor starts missing and vibrating you have a wiring problem that is intermittent.

[Big Manne]

i dont really know much about cars but what about drive shaft?

[tryiian]

im not jesse james but iKnow it`s not the drive shaft or suspension.

do take a look at the drivebelt/fanbelt/serpentine belt/big black belt that goes to all the crap on the front of the motor/and all of these things except a timing belt....

and the alternator, and that wire-testing idea sounded pretty good... and then come tell us what results came from all of this testing and looking.

If the problem doesn`t happen at the usual 2000 revs place in neutral, jack the car up some-safe-how (not by the differential for sure) and try it in gear... just a reckless suggesstion, though iExpect neutral II cause th problem as much as any other gear. A dyno would be a safe place II try this paragraph`s idea...

and didn`t you say something about second gear in the first post? iMean you said giving it gas to get inII second... does it happen in all gears and neutral? how bout reverse? could it by any stretch be a transmission thing?

and last but certainly not least, get er looked at by a respectable auto shop.

[TachyonS14]

This weekend I'm going to do a lot of tests, I'll try to get back to you guys with what I find.

And Tryiian, It is not gear dependent, meaning it will happen no matter what gear it's in, even in neutral.

[S14Life]

Sounds like a wiring problem to me. But all the ideas I would have had have already been said.

And the engine reving at 1k and 1,250 RPM is completely normal.

[tonynalli]

check your spark plugs and the wires. do you know how too tell when one is misfiring. that might be why it is vibrating, but i odnt know why it does it only when it is hot though.

[S14Life]

Simple, that's not the problem

Plus he said he replaced them. Way to read~

[Ubernoober]

It really does sound like an electrical issue.Check your engine temp sensor and thermostat. I realize that normally the ECU would throw a code for this, but intermittent, ya never know. Also, while you replaced the O2 sensor, be sure to closely examine the shielded wire for the sensor. Those things are in a place that can see some abrasive rubbing, particularly since the little plastic holder is the first thing to break in the engine bay.

Definitely check the injector wiring. Like a previous poster said, duplicate the problem if you can, and then wiggle the connectors one at a time. If one is bad, it should be obvious.

Under load suggests that perhaps the knock sensor is malfunctioning? I'm just throwing out ideas here. BTW, my 91 likes only premium. Anything less and it starts pinging.

Check that your EGR is working correctly.

Lastly, perhaps you could buy a spare ECU from a wrecking yard and plug that in if you feel that you have eliminated everything else.