[kdb30]

Guys I need some help.My 99 Mustang GT "stumbles" when cruising down the road.While idling it seems be a little rough,not too bad,just a little.Going through the gears it seems fine.However,when leveling off at highway cruising speed,it seems to jerk a tad.If I turn the defrost on it intensifies pretty good.Anybody know what could be wrong?Thanks in advance!

[Invictus]

clean you IAC, you can't do anything wrong by doing that. and also fluctuations at steady rpm is a symptom of your tps. check the voltage of it and see if it is to spec of not, it can be adjusted or replaced relatively cheap

[steve_stang2003]

Originally Posted by Invictus clean you IAC, you can't do anything wrong by doing that. and also fluctuations at steady rpm is a symptom of your tps. check the voltage of it and see if it is to spec of not, it can be adjusted or replaced relatively cheap

+1

Also clean your MAF and check your air filter /box for contamination or the snorkel on loose etc.
Be VERY careful with the MAF and use only MAF cleaner or isopropyl alcohol.
Don't use carb cleaner as it is too caustic.

[Baneful]

I would like info on this too. My gt stumbles now on the highway at times, but doesn't seem to have any lack of power. I added a 1/2' copper pipe cap with a 1/4 hole drilled out to the iac line before the plastic black box to help the high idle drop. It helped the hanging idle, but it still stumbles at highway speeds while the ac is on. Could this just be the puter is still learning the airflow patterns? It seems every time my car wants to slow down while cc is on it stumbles.

I read it takes about 3 cycles of the ignition to learn the pattern, but I think I am past that.

I also read that the pipe cap worked on older gt's and that I need an iac restrictor plate instead of a cap... One side drilled to the iac hole size and the passanger side hole being smaller (depending on mods)...?

[Garhfer]

Originally Posted by Baneful I would like info on this too. My gt stumbles now on the highway at times, but doesn't seem to have any lack of power. I added a 1/2' copper pipe cap with a 1/4 hole drilled out to the iac line before the plastic black box to help the high idle drop. It helped the hanging idle, but it still stumbles at highway speeds while the ac is on. Could this just be the puter is still learning the airflow patterns? It seems every time my car wants to slow down while cc is on it stumbles. I read it takes about 3 cycles of the ignition to learn the pattern, but I think I am past that. I also read that the pipe cap worked on older gt's and that I need an iac restrictor plate instead of a cap... One side drilled to the iac hole size and the passanger side hole being smaller (depending on mods)...?

wtf? Who told ya adding that crap to your iac line would help?? I wouldn't start adding crap to my iac lines, Just clean out your iac and everything should be fine... why does a hanging idle bother people so much? it hangs for like a second so what...

[40thmustanggt]

i agree its not a bad thing and it isnt going to hurt anything all 4.6 motors have it..

[40thmustanggt]

id try taking that crap off and seeing if it helps your stumble

[acmillr]

Does it stumble under heavy acceleration. If it doesn't, I would have to think it is a TPS problem.

[kdb30]

Ok I have cleaned my IAC.It looked fine but I cleaned it anyway.The air filter and maf all is fine also.The car is fine under any acceleration.It runs like a champ under acceleration.Just at idle it seems rougher than it should.And of course at an even highway speed she stumbles.I guess I need to check the tps.Any pointers from you guys on checking the voltage?Thanks for all the previous advice guys.

[Baneful]

Crap, didn't want to hijack. starting new thread.