jumpy rpm guage [Archive] - GrandAmGT.com Forum


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01-08-2009, 12:46 AM
okay i have had this problem for a while now. i have a 99 grand am gt. when i start my car up already warm, for instance if i stop to get gas, it starts then the rpms jump from like 200 to 800 for a bit. sometimes the car even stalls out. this only happens when the engine is already warm and im starting the car up again. but if i start the car and put it in gear real quick, it doesnt do that wierd idle thing. another thing it does is when i start my car cold, the rpm will go up to about 900 then slowly creep up to around 1100 and bounce a little. and it almost sounds like the engine is gasping for air lol. then it levels out at about 1000 after a couple of seconds. my cousin has the same car as me but when she starts it cold it goes up to about 1300 rpm then slowly goes down as the engine warms. i have a feeling it has to do with something in the throttle body area. i already replaced the IAC sensor and cleaned out the airway and no change. also cleaned off the MAF and no change. does anyone have any idea what could be causing this? thanks for your time.

01-08-2009, 10:37 AM
wait. so it idles at 200 sometimes?

01-08-2009, 11:54 AM
When the engine is idle, can you hear any whisps of air? I wonder if its a vacume leak somewhere. When the engine is warm and expanded, the air is getting in and causing it to run rough.

01-08-2009, 12:43 PM
no it doesnt idle at 200 i said it jumps from 200 to 800 somewhere around there. the rpm gauge bounces up and down up and down. well it does kinda run rough when its started cold too. it seems like it should idle a bit higher.

01-08-2009, 11:14 PM
okay i have a question. you know the vacuum hose that plugs into the FPR, the whitish colored one? where does that lead to? i noticed that when i had the LIM gasket replaced that the guy mustve broken that hose and just used a rubber tube to connect the 2 pieces. i think that hose is leaking and is causing my idle problems so i would like to replace it but dont see where the other side goes to.

01-09-2009, 04:43 PM
it goes to the MAP i believe it is. a little box on the back side of the manifold, should have another hose going right into the manifold as well. how long ago did the rubber hose get put there? cuase when rubber gets heated up a lot it tends to dry out and get cracks in it, thats why they use the plastic stuff

01-09-2009, 06:01 PM
wait my mistake. i meant to say the plastic hose that comes off the front corner of the intake manifold. its a whitish color. where does that lead to? i try tracing it and it just goes into a big bulk of wires.

01-09-2009, 08:02 PM
oh sorry, not sure about that one, i don't wanna move it around too much cause those things break way too easily, especially in the cold

01-09-2009, 10:52 PM
i read some where that your cat or whatever its called on your muffler could be getting alittle plugged up causing more back pressure. making the rpms jump around my car does that sometimes but it jumps up but settles out right away

01-10-2009, 12:36 AM
usually if it was a vaccuum leak you'd have high rmps, not lower

01-10-2009, 12:20 PM
so would it be one of my sensors that messed up? i dont know which one though, it could be MAF or MAP or O2 or EGR idk.

01-10-2009, 01:31 PM
yea if you think its a leak you probbly have to take it to a shop and have them hook up a smoke machine, same with a sensor, they'd have to scan for errors.

01-10-2009, 02:32 PM
Sorry to be an ass, but this is really bugging me. Its a tachometer, please stop calling it an RPM Gauge.

01-10-2009, 04:47 PM
well sorry if im not all technical but it is a gauge and it does show the RPM of the engine. dont read my posts and you wont have to worry about it then.

01-10-2009, 04:48 PM
and yeah i was thinking about bringing it to a garage and have them smoke test it. how long does that process usually take?

01-10-2009, 05:18 PM
well it took them about 3 hours to diagnose and replace my EGR valve, that includes how long they had to wait for the part

01-11-2009, 10:19 AM
wait my mistake. i meant to say the plastic hose that comes off the front corner of the intake manifold. its a whitish color. where does that lead to? i try tracing it and it just goes into a big bulk of wires.

ok that plastic tube also has to do with ur map. u have 2 tubes one from the front that goes in with ur wirering harness and the other coming out the uim right next the the little black box that is the maf sensor.

now the surging could be a few things, first are uy throwing a ses??? if u are i could be the maf which could of gone bad, or the egr valve. another think is if your intake tubinging had a leak in it, ecspeacally after the maf. or you could have a sizeable leak in ur uim.

when ur friends car is starting out at high idel thats just his car warming up like its sapose to. most likely your problem is the maf or egr. just go to an autozone and have them read your codes. another way to find out if its ur maf or egr is to unplug ur maf and start it up and see if its still surging.

when i put my sc on u got rid of my egr and it wasent properly block off so it would surge and sometimes die, and when i unpluged the maf it would idel fine. because i had a massive air leak.

just dont be too soon to relace one thing or another and waste money. be sure what it is that u need to replace

01-12-2009, 05:45 AM
i am not getting any service engine soon light. i havent in over 2 years ;) yeah that hose that broke on me was the one that connects to the UIM right next to the FPR. it goes over the UIM to the back and is mixed into a big bunch of wires wrapped in tape and whatnot. yeah i would think my car would idle a bit higher when its this cold out. i unplugged the MAF and it made the idle jump around even more. and when i drove, the transmission would slam into the gears. i didnt try with the EGR unplugged though.

01-12-2009, 03:38 PM
well u i ment to just let it sit there its not good to drive around without the maf. it might be alright if ur completly stock. and i wouldnt suggest unpluging the egr cause i have no idea what it would do lol. but you caould try a block off plate. ull get a lil more power put ul have a ses on all of the time unless u have a tuner and you can disable the ses code for it. you prolly have an air leak somewere. but i would have no idea were it would be at. and you can make a block off plate with a lil sheet metal and i would suggest using some ultra gold copper silcone sealent or whatever the fock its called. that what i used to block mine off. and i dont have a problem with the ses light being on. can ill entually disable that code im just to lazy right now

01-13-2009, 12:26 AM
yeah im leaning more and more towards a vacuum leak. because it does the jumpy idle when cold and warm. i just picked up a spray can of starting fluid at walmart earlier so ill spray around tomorrow. any common areas that i should spray where there would be a leak?

01-13-2009, 05:50 PM
ahhh around the upper plenums on ur uim. around ur egr, tb. and intake. and one place to check would be theres a plastic tube from ur back valve cover that goes to ur intake. i beleave that that is a vacuum line. not 100% sure. its kinda a guees and look type thing with vacuum leaks

08-24-2010, 10:31 AM

08-24-2010, 10:40 AM
sorry i still have no clue how to post a new message cause iam new lol. im having problems with my 99 grand am gt sometimes starts up rough and idels high in drive but in park goes even higher doesnt always do it but is becoming more frequent if any1 can help please send me a message thanks every1 :applause: