Rough Idle only in Drive

[Matthew]

Hey Everyone. I have a 94 Firebird 3.4 V6 with about 135,000 miles on it. For the past six months now I've had a problem with it idleing rough when stopped at intersections and such. The car idles slightly rough when in Park and Neutral, but the entire interior of the car vibrates from the idleing of the car when it is in drive. I just recently changed the plugs and wires in the car thinking that might be it, but no luck. I check the IAT & IAC sensors and they seem to be functioning. I'm thinking about replacing the IAC sensor just in case that might be it. Does anybody have any suggestions as to what might be the cause of this problem. Thanks

[GregWS6'01]

Welcome to the board! It won't be your IAT sensor.......Does it do it when you have it in neutral? You could have a misaligned driveshaft...slow fuel injector.....did you make sure the plugs were gapped correctly to .045??

[Backfire]

I actually have the same problem on my 94 A4. The car idles at a steady 750rpm(atleast by the tach it's steady) when in drive or reverse. But there is a ton of vibration throughout the car. As soon as I raise the rpms at all, the vibrations go away. But when I am sitting still in gear, it feels like the interior panels are gonna fall off. I have stuffed so much foam in all the corners and cracks to try to stop the rattling but it is still there :mad: .

Plugs, wires, O2 sensors, fuel filter, air filter, oil, IAC, throttle body, and PCV valve have all been replaced or cleaned recently. I am stumped as well. As I performed these repairs, I figured one of them would solve the problem, but no luck. Could the torque converter not provide the necessary slip at idle, causing excess drag? I have never heard of that but I am out of other ideas. The fluid level is good, and its color is still red. There are about 20K miles on the fluid and filter.

[I Hate Rice]

Hello...Anyone out there ?? Well anyway I'm new here and just checking everything out. I do believe I have the sollution to your "vibration" problem... Have you changed your tranny fluid recently?? I'd bet my MSD thats it .Trust me a flush will do wonders.

[veesix]

You could also look for a vacume leack in your car. I do not know how the 3.4s' are set up but my cousin has what sounds like the same problem that you guys are having and he found that it was a brake vacume like that was broken. If it only shakes when you are parked and your foot is on the brake, I would bet that this is your problem/ Good luck I hope that his helps!

[Backfire]

As long as the car in still, or just creaping along, at idle it will shake. It doesn't matter if I have the brakes applied or not.

I posted that my trans fluid has about 20K on it and still looks to be in good condition. Can you explain why the fluid would cause the problems we are having?

[predator5100]

Hey saw this old post and i'm having this exact problem not the mounts either changed mine and all i think it could be a torque converter there are times mine is noticable and times when its not

[EyeOutThere]

<blockquote>quote:</font><hr>Originally posted by I Hate Rice:
...I'd bet my MSD thats it .Trust me a flush will do wonders.<hr></blockquote>

That's a deal! I am going to hold you to that :D j/k.

[EyeOutThere]

<blockquote>quote:</font><hr>Originally posted by Matthew:
Hey Everyone. I have a 94 Firebird 3.4 V6 with about 135,000 miles on it. For the past six months now I've had a problem with it idleing rough when stopped at intersections and such. The car idles slightly rough when in Park and Neutral, but the entire interior of the car vibrates from the idleing of the car when it is in drive. I just recently changed the plugs and wires in the car thinking that might be it, but no luck. I check the IAT & IAC sensors and they seem to be functioning. I'm thinking about replacing the IAC sensor just in case that might be it. Does anybody have any suggestions as to what might be the cause of this problem. Thanks<hr></blockquote>


If it does it only when the engine is warm, and the oil pressure drops when it is happening, then it is probably your "Oil Pressure Sending Unit"

[xFactoRx]

heh, i have the answer to your problems. my 94 firebird auto 3.4 does the same thing... until i changed the main bearings. When you at idle there isnt enough oil pressure to keep your crank at the center position with oil surrounding it evenly. so the crank vibrates against the main bearings. before to diagnose the problem put in a thick oil. like 15w-50 or something THICK. it will kill the vibration because the oil still stays all over the crankshaft and doesnt allow it to move about.

so basically, put in thicker oil or change the main bearings... just its expensive to do so.. thats why i did it myself.

hope this helps

[Shadly]

It sounds like you're dropping a cylinder at low RPMs. If this just occurred all of the sudden(not gradually getting worse over the last few years), you might want to check for a dropped cylinder. At idle, pull a spark plug wire. If the RPM drops, put it back and move to the next one. If you find one that doesn't change the RPM, that's it. Check the plug gap, the wire, and the coil pack.

[RedbirdV6]

Just the signs of getting old, look at your mileage, it isn't gonna run like a new one, it happens ;) :D

[predator5100]

I dont think either are it i just had the whole engine rebuilt unless for somereason they didn't chaneg my oil sending unit

[EyeOutThere]

<blockquote>quote:</font><hr>Originally posted by predator5100:
...unless for somereason they didn't chaneg my oil sending unit<hr></blockquote>

They most likely didn't

[predator5100]

umm whats an oil sending unit and are they hard to put in