Car Vibrates when idling in drive

[Leo]

Car is a 1991 Pontiac Sunbird Le, Automatic. Car idles perfect in Park and when you have any throttle open at all in drive it runs great. It just when its in Drive and idling at a stop light, it vibrates. Any ideas? No stalling issues at all but it feels rough at stop lights.

Topic

[Daniel Weith]

A few questions:

1. Is this a 4 or 6 cylinder engine?

2. Is this a new symptom?

3. Is this car new to you?

4. Is the Check Engine light on?

[Leo]

#1: V6 3.1L
#2:Not a new symptom been a issue since bought
#3:Not new owned 2 years almost
#4:Never had a check engine light ever 🙂

Thanks BigDanIL279

[Daniel Weith]

The 3.1L Engine when running correctly is a smooth idle, but my gut is screaming motor mounts.

With a bad motor mount even the smoothest running engine will bounce around just due to the nature of the beast. In this case six (6) controlled explosions confined in a tube to produce energy and propel you down the road.

The mounts themselves might not be broken, but the rubber bushing on the lower mounts may be brittle and no longer provide the damping affect as when they were new and soft.

Due to age of the vehicle and the extreme conditions they experience I would start there with a visual inspection of the top and bottom mounts for signs of missing rubber or broken mounts..

Please keep us updated..

Daniel

[Leo]

nature of the beast

lol 😛 will do

[EricTheCarGuy]

A lot of possibilities here, but start with engine performance before you go to engine mounts. Detailed information on solving idle problems. can be found here.

http://www.ericthecarguy.com/faq/solving-automotive-idle-problems

Please keep us updated on your progress.

[Leo]

Thanks ErictheCarGuy you rock!! I’ll have to consider all possibilities for sure.

I have a new IAC Valve. It erases engine values related to IAC if you disconnect the battery at all.

to relearn these values,I’ve read on a post that for this engine(Lh0) you need to
#1:Turn off all AC
#2:Block wheels And Apply Parking brake, shift to drive,run for 10 minutes no throttle,
#3 (Repeat #2 but 5 minutes of run time,not 10)

Seemed to work fine when i did this work a couple months ago 🙂
Everything runs fine. As I Replace parts, thing tend to be running smoother 🙂 I just want it to to run perfect…

[Mike Miller]

I’ve been hunting down issues one by one with my 2000 Ford Focus DOHC for the last two years.
First step was replacing the rotted vacuum lines under the hood…a step in the right direction and a little smoother. That included PCV valve and related hoses for that. I too have a IACV on hand and ready to replace, but because of where the blasted thing is on this car, I’ve been putting it off.
Today….yes today, I replaced the lower motor mount….and it was thoroughly spanked and there was immediate improvement. Two more mounts to go, but I ran out of daylight and its getting colder here in PA, and I’m getting older doing this in my backyard…lol

my 2₵

[Author]

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