1999 GT Runs Rough

Crazy Tater Tot · December 5th, 2011, 05:52 PM

Hi, I have a 1999 GT Vert and its been running rough, but ONLY when the engine is warm (after driving for about 15 minutes), when idling at a stop light the rpms bounce up and down(they move about 300 or so) but they shake the car when they bounce. Any ideas? It just started doing it last week. Could it be the spark plugs or a misfire? --- And it does have about 119k on it.

Macunicorn · December 5th, 2011, 06:00 PM

Car sounds like it needs a tune up. New plugs, fuel and air filter etc.

nysiv16 · December 5th, 2011, 06:08 PM

i would also try cleaning the IAC with some carb or MAF cleaner...sounds like its idling bad

Kohrs93 · December 5th, 2011, 08:10 PM

Does it have a lope to it at idle? Mine did when I was having a misfire. Ended up being a bad COP, which i figured out by a check engine light that told me where the misfire was.

PsnSnake_19 · December 5th, 2011, 08:14 PM

Spark plugs

3valveStallion · December 5th, 2011, 08:14 PM

clean the Throttle Body, possibly new plugs or alternator

Crazy Tater Tot · December 6th, 2011, 04:39 PM

Thanks, But I just changed the air filter a month ago and am planning to replace the fuel filter soon. Its not throwing a "Check Engine Light" but could it show something if I had it scanned? & any kind of plugs are the best?

cschoening09 · December 6th, 2011, 11:37 PM

original motorcraft plugs are the best you can get for these cars. and im not a keep things origonal kinda guy

Crazy Tater Tot · February 1st, 2012, 07:01 PM

Allright problem solved, btw sorry it took so long to post back lol , It was my plugs they were fouled because I had coolant leaking into the intake system... yeah it was a cheap $700 dollars to fix at my local shop :/ but on the bright side, the stangs all better now!

PsnSnake_19 · February 1st, 2012, 07:28 PM

Nice to hear man, i told you it was the plugs haha

cschoening09 · February 1st, 2012, 11:11 PM

so , new intake manifold solved it? or just gasket?

Crazy Tater Tot · February 1st, 2012, 11:34 PM

Yup, new manifold.

Cabikejumper · February 2nd, 2012, 01:20 AM

Hopefully you got a aluminum crossover manifold...

Crazy Tater Tot · February 5th, 2012, 11:31 PM

Yeah I made sure it wasn't a cheap plastic one like what was on there.

December 5th, 2011, 05:52 PM	#1
Crazy Tater Tot Regular 1999 Mustang GT Vert Join Date: Nov 2011 Location: Clinton, Iowa Posts: 82 iTrader: 1 reviews	1999 GT Runs Rough Hi, I have a 1999 GT Vert and its been running rough, but ONLY when the engine is warm (after driving for about 15 minutes), when idling at a stop light the rpms bounce up and down(they move about 300 or so) but they shake the car when they bounce. Any ideas? It just started doing it last week. Could it be the spark plugs or a misfire? --- And it does have about 119k on it. Last edited by Crazy Tater Tot; December 5th, 2011 at 07:13 PM.

December 5th, 2011, 06:00 PM	#2
Macunicorn Hardcore Enthusiast Join Date: Jul 2011 Location: Huntington Beach, Ca Posts: 1,219 iTrader: 0 reviews	Car sounds like it needs a tune up. New plugs, fuel and air filter etc. __________________ Sig by Tricep

December 5th, 2011, 06:08 PM	#3
nysiv16 Regular 2000 mustang gt Join Date: Nov 2010 Location: NY Posts: 114 iTrader: 0 reviews	i would also try cleaning the IAC with some carb or MAF cleaner...sounds like its idling bad __________________

December 5th, 2011, 08:14 PM	#5
PsnSnake_19 Hardcore Enthusiast 2001 cobra Join Date: Aug 2010 Location: tampa Posts: 2,251 iTrader: 0 reviews	Spark plugs __________________ SVT all day! Next mods: Mickey thompson street radials, new wheels, gears and tuner, then turboed by 2013

December 5th, 2011, 08:14 PM	#6
3valveStallion NOR*CAL's FINEST 2006 Mustang GT Established in the back of a Boss 429 circa 1988 Join Date: Nov 2011 Location: Roseville, CA Posts: 639 iTrader: 0 reviews	clean the Throttle Body, possibly new plugs or alternator __________________ (BBK TB)(JLT CAI)(BMR A-Arms)(J&M LCAs)(Pypes C-back)(BAMA93)(PS LTs)(PS O/R H)(Steeda CMDPs)(Prothane Bullet Mnts)

December 6th, 2011, 04:39 PM	#7
Crazy Tater Tot Regular 1999 Mustang GT Vert Join Date: Nov 2011 Location: Clinton, Iowa Posts: 82 iTrader: 1 reviews	Thanks, But I just changed the air filter a month ago and am planning to replace the fuel filter soon. Its not throwing a "Check Engine Light" but could it show something if I had it scanned? & any kind of plugs are the best?

December 6th, 2011, 11:37 PM	#8
cschoening09 Hardcore Enthusiast 2001 Mustang GT 9.30 @ 77mph-1/8th mile 2.2 60' Join Date: Oct 2010 Location: Council Bluffs, IA Posts: 1,704 iTrader: 3 reviews	original motorcraft plugs are the best you can get for these cars. and im not a keep things origonal kinda guy __________________ 01 GT. 5spd , 03-04 cobra clutch, on its 2nd 4.6l motor2nd tr3650 too,JLT CAI,UPR o/r x, magnapack catback, predator tuned, H&R ss 10.5" bullitts w/ nt555r DR's

February 1st, 2012, 07:01 PM	#9
Crazy Tater Tot Regular 1999 Mustang GT Vert Join Date: Nov 2011 Location: Clinton, Iowa Posts: 82 iTrader: 1 reviews	Allright problem solved, btw sorry it took so long to post back lol , It was my plugs they were fouled because I had coolant leaking into the intake system... yeah it was a cheap $700 dollars to fix at my local shop :/ but on the bright side, the stangs all better now!

February 1st, 2012, 07:28 PM	#10
PsnSnake_19 Hardcore Enthusiast 2001 cobra Join Date: Aug 2010 Location: tampa Posts: 2,251 iTrader: 0 reviews	Nice to hear man, i told you it was the plugs haha __________________ SVT all day! Next mods: Mickey thompson street radials, new wheels, gears and tuner, then turboed by 2013

February 1st, 2012, 11:11 PM	#11
cschoening09 Hardcore Enthusiast 2001 Mustang GT 9.30 @ 77mph-1/8th mile 2.2 60' Join Date: Oct 2010 Location: Council Bluffs, IA Posts: 1,704 iTrader: 3 reviews	so , new intake manifold solved it? or just gasket? __________________ 01 GT. 5spd , 03-04 cobra clutch, on its 2nd 4.6l motor2nd tr3650 too,JLT CAI,UPR o/r x, magnapack catback, predator tuned, H&R ss 10.5" bullitts w/ nt555r DR's

February 1st, 2012, 11:34 PM	#12
Crazy Tater Tot Regular 1999 Mustang GT Vert Join Date: Nov 2011 Location: Clinton, Iowa Posts: 82 iTrader: 1 reviews	Yup, new manifold.

February 5th, 2012, 11:31 PM	#14
Crazy Tater Tot Regular 1999 Mustang GT Vert Join Date: Nov 2011 Location: Clinton, Iowa Posts: 82 iTrader: 1 reviews	Yeah I made sure it wasn't a cheap plastic one like what was on there.

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