87 GN at idle

W

westcoastgrandnational

Member
Joined
May 28, 2014
hey guys i have a 90k original mile 87 grand national which appears to be 100% stock and when its at idle in Park, the motor seems like it has a tiny miss, engine shakes a tiny bit, is this normal for grand nationals? Ive heard alot of them do that, heres what ive changed and checked for, new spark plugs, new sending unit, new fuel pump, new fuel filter, new idle air control valve, cleaned the mass airflow sensor, and have checked for vacuum leaks already.
 
Mine did the same thing,get a ECM chip from Eric TT and a translator with an ls1 or lt1 maf BIG diffrence once you do that.


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You need a new chip for the computer about $85. Because your almost 30 year old 1 is very old technology and don't agree with today's fuel also those first generation maf's are to old mine worked good enough but once I replaced it with a translator and a lt1 maf night and day diffrence.


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Do you have a vac/boost gauge? My 87 gn recently had ignition problems which I didn't realize because it seemed to idle fine but was horrible when you would try and get on it... Anyways if you have one hooked up you should be reading a steady vacuum at almost 20in. If it's fluctuating between 1-2 in. Constantly it could mean you have an ignition problem like I did 4-5in fluctuations could mean leaking valve seals there's a couple other symptoms you can see through the gauge if you google them like I did... Just a thought

I over looked what was wrong with mine from visually ruling it out but the gauge told me other wise and in your case it won't hurt a thing to go pick up a aftermarket vac/boost gauge

Good luck!
 
Now yesterday i turned it on cold start and the idle went high and wouldnt drop back down it was stuck at like 2-3k RPM until i turned the car off and back on when the idle went back to normal. Are these an other indications of what might be wrong. And im also looking into the chip but not sure if this also has anything to do with it???
 
I would check the cam sensor as it plays a big part in the ignition system, take the cap off it make sure there are no loose or broken parts and that the shaft going into the engine isn't spinning on it's own. And a chip is always a good thing to get from what I've seen a turbo tweak chip is the way to go although I'm running my mag 4 chip until I upgrade to ls1 maf and translator.
 
westcoastgrandnational said:
with the turbo tweak chip do i have to change anything else on the car besides the chip? Can i leave everything else stock?
Click to expand...
You don't necessarily need to change anything else for the new TT chip to work but you might want to consider an injector and chip package. If you only buy the chip now and decide to change injectors later it will cost you $55 to update the chip. When it comes to mods its usually best to have a goal to shoot for (stock? 12 sec?, 11 sec? faster?). That way you can buy the right parts ONCE and minimize out growing parts too quickly.
 
Agreed ^^^

Also tho remember your parts are nearing 30 years old regardless of miles if it wasnt well maintained it's whole life I'd still double check everything you can think of
 
Do you guys suggest also replacing the egr valve also?? And I plan to keep this car stock no crazy 10-11 sec race car I just want a nice running dependable driver GN
 
The TT chip disables the egr function so its really not needed. Some just put a block-off plate on the intake and remove the egr components. But if you ever need to run an emissions test you'll need to put it back on so keep it in your parts stash just in case. I still have mine on just to retain the stock look. I did replace mine a year or two ago because it developed an oil leak at the stem area.
 
the car does have a little exhaust leak at the bottom of the exhaust manifold where there is a crack not sure if this has anything at all to do with it
 
Stock chips have too much timing even for 93 octane fuel and the cold start on the stock chips are known to be just horrible.

If I were you I would fix all your known problems.. Any leaking oil your exh. Leak then get a TT chip and see how it is after that
 
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