Engine surging with A/C on, 99 GT

OV10stang

Member

Aug 7, 2005

48

0

16

Pembroke, NH

Jan 21, 2006

#1

• Jan 21, 2006

• #1

When I'm driving, with the A/C on, the engine surges big time, it sucks to drive with the a/c on, but I live in FL and need it. A/C blows cold air, but when the surge occurs, I hear a vent/duct slamming shut under the dash. Also, when at idle, the a/c cyles, and the idle jumps up and down every min. or so. Did a search, didn't come up with anything solid. Saw it might be IAC or an A/C pressure sensor.... Anybody seen this before? I could just start shot-gunning parts, but hate to replace an IAC or anything else for that matter, when I don't have to.

 

D

d90212

Founding Member

Jan 17, 2000

253

4

0

kailua, hawaii

Jan 21, 2006

#2

• Jan 21, 2006

• #2

did you disconnect the battery or change the battery recently? had to recharge a battery because it was dead?

 

OV10stang

Member

Aug 7, 2005

48

0

16

Pembroke, NH

Jan 21, 2006

#3

• Jan 21, 2006

• #3

I have disconnected it before, before doing my sct tune. Why do you ask?

 

D

d90212

Founding Member

Jan 17, 2000

253

4

0

kailua, hawaii

Jan 21, 2006

#4

• Jan 21, 2006

• #4

because you have to relearn idle strategy again. disconnect the battery, and idle the car with all accessoriess off and the a/c in the off position.

when you reconnected the battery, you might of had the a/c on while relearning the idle strategy. started it up with the a/c on, and learned an idle strategy that already has a load on it. thus dropping the rpms even lower when the load is off.

 

OV10stang

Member

Aug 7, 2005

48

0

16

Pembroke, NH

Jan 21, 2006

#5

• Jan 21, 2006

• #5

The car does it up thru the rev range, while cruising down the road @ 2000 - 2500 rpms, or even higher, it will constantly cycle the a/c(even though it's blowing cold) and when this happens, the car surges, with a noticeable loss in power everytime it does this.

 

D

d90212

Founding Member

Jan 17, 2000

253

4

0

kailua, hawaii

Jan 21, 2006

#6

• Jan 21, 2006

• #6

guess it may be time to look at your sct tune, since it all started after the tune.

 

OV10stang

Member

Aug 7, 2005

48

0

16

Pembroke, NH

Jan 21, 2006

#7

• Jan 21, 2006

• #7

Reflashed to stock, still does it. Put the tune in before I really had a chance to drive the car, I don't remember if it did it before I did the tune, only drove it home from the seller's house with the stock tune, and parked it.

 

OV10stang

Member

Aug 7, 2005

48

0

16

Pembroke, NH

Jan 22, 2006

#8

• Jan 22, 2006

• #8

Well, I just went out and troubleshot it. Disconnected the A/C press switch and jumped the connector, now it works great. So now it looks like either a borderline A/C charge, or press switch is bad. A/C still blows cold though.

 

K

Kilgore Trout

Fried or Broiled ?

10 Year Member

Mar 30, 2005

4,749

95

134

Jan 22, 2006

#9

• Jan 22, 2006

• #9

Usually the cause of this problem is low freon. Recharging it should fix the problem. A low charge causes the compressor to cycle on and off too quickly which lags the engine.

 

jstreet0204

Active Member

Jun 26, 2003

939

0

36

Winston Salem, NC

Jan 22, 2006

#10

• Jan 22, 2006

• #10

Kilgore Trout said:

Usually the cause of this problem is low freon. Recharging it should fix the problem. A low charge causes the compressor to cycle on and off too quickly which lags the engine.

Click to expand...

+1 The tune shouldn't have anything to do with it.