'00 GT Vert surging ???

Az Pete · Oct 4, 2006

Stock GT that runs great with 58,000 miles, auto, 22.5 mpg. Idle is fine with out the A/C running. Turn on the A/C and the idle will sometimes jump to 1500 and down to about 400. Cruising is also bad with A/C on. I can feel the surging while on cruise control, on level ground. Feels like a strong, gusty head wind hitting the car. I do not see a change in the tach or speed while cruising. A/C clutch is NOT kicking in and out during this. I guess it is not the IAC as it is bad at speed also but..... Any ideas?

TweekedGT · Oct 4, 2006

Mine does the same thing with both the A/C and heat on. I think it's normal actually unless you're getting a real bumpy ride from it. I can feel mine lose power as soon as I turn either on, even with the blower.

Superhereaux · Oct 4, 2006

Az Pete said:
I guess it is not the IAC as it is bad at speed also but..... Any ideas?

i think the iac functions all the time, not just at idle

when the a/c kicks on it places a load on the engine, if throttle input is constant at cruising speed rpms will drop and the vehicle will slow down, the iac will compensate and keep the vehicle going at the same speed. i could be wrong though

Az Pete · Oct 4, 2006

This has never happened on our '01 F150 or either the '93 or '96 Cougars we owned so I would think what I feel is not normal, especially the variance at idle. I realize that the idle speed will change a bit with the A/C on but not a surge up to 1500 rpm. This is also not a result of the compressor starting or stopping. It is way to much surging for it to be the compressor. Guess it might be a dealer question.....

Superhereaux · Oct 4, 2006

just to be clear, the car runs perfectly with the a/c off right?

Az Pete · Oct 4, 2006

As best as I can tell, it idles fine and runs great. Acceleration is strong and cruising is smooth. A/C works good also, just adds the surging to the idle and cruise.

BurningRubber · Oct 4, 2006

Mine will surge to rougly 1k rpm at idle if I switch the AC on. Also when cruising and I put the AC on it sucks the life out of the car. Same as my Jeep. AC sucks power and thats normal.

As far as your idle dipping to 400rpm thats not. Thats sounds like it might be a sign of a bad IAC (too common). You can try to clean it out and see if that helps out.

Az Pete · Oct 4, 2006

I realize that the A/C will pull some power but not like this surging. I have had A/C in everything from a '67 1100 cc Datsun pickup to full size pickups so I know how power can be lost. This really feels a lot different than just normal A/C loss.

hotdog71 · Oct 4, 2006

sounds like a question for the master svttech

I know when I put on my BBK75 mm TB/P combo my AC on idle is a little rough but nerver over 1k rpm between 850-1000 rpm.
I know it had nothing to do with my IAC because it was chaged to try and fix the surging on de-cel @ 35-40 mph

the98stang · Oct 5, 2006

I've been fighting my 00 GT FOREVER. I have the same problem. Crazy ass idle with the A/C on. Sometimes when I brake she'll drop to 500 rpm for a split second. And it happens right as the car comes to a complete stop, not WHILE braking. So I think it may be related to the master cylinder/braking system some how.

Anyway, I've replaced the PCV, TPS, and IAC and it ran much better. Cleaned all the MAF and most electrical sensors too. The idle will drop sometimes, but for the most part it's ok. I would clean the IAC first and see if that helps. That's free anyway .

FivePointStang · Oct 5, 2006

My 2000 GT Vert does the same thing too. Weird.

Does it happen to be black too?

the98stang · Oct 5, 2006

FivePointStang said:
My 2000 GT Vert does the same thing too. Weird.

Does it happen to be black too?

mines black

damn idle

SilverBullet00 · Oct 5, 2006

I think its a problem with the 99-00's. I have a surging problem with the AC on and off. I push in the clutch shifting gears or coming to a stop and the RPM's shoot up 200-300 rpms.. very annoying.

If you do a search at some of the other stang sites around, there are tons of threads with guys that have 99-00's with similar problems- some are solved with a new IAC, some with a new computer and some just stop on there own. Some have even gone to have a dyno tune just to get rid of the surging which didnt work... Almost makes me sick thinking of how many hours I have put into getting my car running right..

I took my car to a guy here in town that said it was due to a parameter in the computer called the "transfer" function that aparently a tuner can fix. It has something to do with the MAF and the O2's along with the vehicle speed sensor? I have no idea if thats true or not though..

Az Pete · Oct 5, 2006

Local dealer says to look for vac.leaks. I doubt that but will look into it. BTW, mine is red but has a black top.

matts90gt · Oct 6, 2006

Replace the cycle switch. Should solve your problems. $20 part

Spidey · Oct 6, 2006

I get this on my 99' GT Vert as well.

Az Pete · Oct 6, 2006

Hmmmm, will do the cycle switch thing this week. Thanks........

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