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97 grand prix gt idle problem

J

jmsal26

New member
I have a 97 grand prix gt and when i rev on it and just let the rpms come back down they drop lower then normal but come back to normal it goes about 200 to 500 rpms below normal depending on how high i rev it and also going down the road sometimes and when i lift off the gas the rpms drop down but then pick right up iv changed the*idle*air*control*valve
*and it runs good and idles fine it has plenty of power and the throttle responce is good and it only acts up every now and then it doesnt do it all the time what can be causen this
 


Almost sounds normal to me. Figure when you are going down the road and depending on gear it will come out of lock and drop rpms or raise rpms then go back to normal once the throttle is applied again.

In park if you rev it some and then just let off I've seen them drop down to 500 rpms and as quick as the car can raise it back up to 700-800, I think its because the IAC is not needed at the time you are reving it then when you let off there is a delay for when it comes back on. But I'm just guessing here.
 
Its only done it going down the road 3 times 1 time when i was slowing down from 60 and there other 2 times slowing down around 30 to 40 the car only has 141,000 miles on it and someone told me that is could be a vacoum leak or the throttle body is dirty or bad but i figuerd if that is wats wrong with it it would do it all the time not every now and then and it mainly does the idle drop after rev when its not warmd up its done the rpm drop when it was at normal temp iv ownd the car for two years and its the first time its done it going down the road its done the idle drop after rev almost as long as iv ownd it
 
As long as it doesn't stall its not a problem. A tiny vacuum leak and dirty throttle body can cause it, might as well clean the TB as maintenance if it hasn't been done. Check vac. lines under the hood while you're there.
 
Iv been thinkn about cleaning the tb i just dont know how hard it is to take it off plus wat would be the best thing to clean it and should i take out all the sensors on the tb when i clean it and should i replace the gasket onit to while its off
 
Not hard to remove. Yes replace the TB gasket. Remove all the sensors and clean it with throttle body cleaner you pick up at any parts store. Make it shine. Pay attention to the backside of the thottle plate as this will have 95% of the carbon on it. Would also be a good time to get a can of MAF cleaner (do NOT clean it with anything else) and clean that while you're at it.
 


remove the maf, if you want to, you can leave it on the engine and clean it up. take the air filter tube off, then theres a ring clip that holds the screen in place, get that out, then use a old tooth brush and carb cleaner to clean the back side of the butterfly flap, and behind the flap. and edge of the flap. you can spray in there, then scrub with the old tooth brush while holding the throttle open, then wrap a rag over the brush, re spray wipe it down. you may be able to get your fingers deep inside as you can as well.


or take the throttle cables off, unplug all the sensors, then un bolt it from the intake, and clean it that way, removal cleans up best, but you'll need a new gasket.
 
buy maf cleaner, re move the maf, then spray the 2 wires in the tube of the maf, dont touch them or scrub, just spray them with the cleaner, let it dry, re install it.
 
As soon as i can get the gasket and both the cleamers ill do it and let everybody know if it workd plus if its a vacuum leak does anybody have any idea where it might be at iv lookd at all the vacuum lines and i didnt see any broke or craked they all lookd good plus this car has very few vacuum lines on it iv had other cars with 3 times as many lines
 


While you are there.. why don't you take a moment and look at your vacuum lines. It's totally free to stare at your engine.
 
I cleand the throttle body and the mass air flow sensor today and after i got everything back together it wouldnt start at first then i messd with the throttle position sensor wire plug and then it startd but idled high at 2000 rpm and the check engine light came on then i cut it off and unlugd the battery waitd 15 mins and startd it again now its at 1500 rpms and very slowly climbs to about 1600 or 1700 rpms also i didnt put the gasket on cause i just got the new upper intake put on it 2 months ago and the old gasket still lookd good and i think i might have adjusted the cruise control wrong on the tb but i wouldnt think that would have anything to do with it idling high and im talkn about the spot u can adjust right on the tb not on the braket that holds the cruise control wire
 
you may have put the tps in wrong if you took it off.

or your getting a vac leak via the gasket, if you failed to clean the old one off all the way.

at idle, both throttle and cruise cables should have a touch of slack to them, not tight and taunt.
 
I took the tps off when i did it and it would only go in one way cause when u put it in u gota put it so that u have to turn it so it will line the holes up and i put it in with the plug facen down some then turned it up so it would line up and iv had it do this before when i started it it would idle at 2000 and the check engine light came on also that little braket near the tps that bolts to the side of the tb i forgot to move it when i put the tp on and i had to forse it past the tps sensor could i have messd that sensor up by doin that cause i had to push on that braket kinda hard to get it past the sensor
 
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