1987 GN runs pretty rough at idle

[trucky12]

Hello boys Im back. I had a 84 and sold, now I finally got my 1987 and I love it. Just one thing though, actually 2. It has all the power in the world I can imagine, but at stoplights it idles rough and can even rattle dash, you can feel it pretty good, but again it goes nuts when you get on it. Also, what are the rpms on average suppose to be at when cruising 70mph, the light goes to 5k, is this right?

 

[1chance]

Rough idle maybe MAF going bad, mine dose that, but it does that cause i took out one of the screens, and if you got a overdrive trans, that's not right, i have a 350 trans, and 70 mph yeilds 3000rpm.

 

[Heg87t]

Hello boys Im back. I had a 84 and sold, now I finally got my 1987 and I love it. Just one thing though, actually 2. It has all the power in the world I can imagine, but at stoplights it idles rough and can even rattle dash, you can feel it pretty good, but again it goes nuts when you get on it. Also, what are the rpms on average suppose to be at when cruising 70mph, the light goes to 5k, is this right?

Congrats on your purchase.

You NEED to get a scan tool of some type to diagnose this properly. You need to check the obvious easy things first: Fuel filter, plugs wires, coil, fuel pressure, IAC reading, TPS setting, air filter TCC solenoid, vacuum leaks, exhaust leaks, and many more.

Check out the "Spring Cleaning" at gnttype.org and read the many posts hear about diagnosing rough idle.

Stock tachometers and boost gauges are rarely correct. My tach is about 700 rpm high. Scantool will tell you what the rpm is also.

 

[trucky12]

thanks guys, all help is greatly appreciated!!

 

[bosted86]

Hello boys Im back. I had a 84 and sold, now I finally got my 1987 and I love it. Just one thing though, actually 2. It has all the power in the world I can imagine, but at stoplights it idles rough and can even rattle dash, you can feel it pretty good, but again it goes nuts when you get on it. Also, what are the rpms on average suppose to be at when cruising 70mph, the light goes to 5k, is this right?

dont trust the rpm dash lights, they are usually way off as our cars are old and the back is probably corroded. mine engine shakes alot also when im at a light. all readings are good on scanmaster. im think maybe a motor mount or trans mount. my old trans am started vibrating and shaking and it was found to be a trans mount.

 

[billhead]

what kind of chip are you running? some of reds chips idle like crap

 

[trucky12]

all I know is it had a factory defect chip and that was replaced with a performance one, what kind it is I have no clue, how do I findout!

 

[Double-L]

First thing you need as the guy said a scan tool like a scan mater 2, Next you have to have a chip for what you are running, It is nothing for a stock GN with a K&N filter and turn the boost and fuel pressure up and run 12's but you want to know about the rough idle, I would have everything checked out, Plugs, Wires, Have some one run a test on it but when mine had a stock block it was rough to but as you said run like crazy, I run a best of 11.18 at 126 and had the engine rebuilt and had it internally balanced and that made it feel like a new car,