Hey, I am not exactly sure when the cruse started causing me problems but I noticed it right after I did my MAF conversion. Just before that I did notice a little bit of a surging with the cruise on just not nears as bad as now. What is happening when the cruise actually works is that it will not really hold its speed it will jump up and down, sometimes only 1-2 km/h and sometimes 5 km/h jumps. With my foot near the gas pedal when it is doing this the pedal is constantly going up and down. It does this all the time when cruse is on, that is when it actually works. Sometimes I cannot even get cruise to work. What I have checked so far is that the plug on the transmission is all the way it and it is and that the connections to the cc box under the dash to the left of the clutch pedal are all the way in and they seem to be. With the MAF conversion I did tie into two of the existing wires going into the cc box for the maf computer but I don't see how this would mess up my cruise seeing as I did not cut the existing wires just cut the insulation off about an inch of each of them and soldered the wires for the computer onto them and then taped them up really well. I have checked everything I could think of with no good results so far. If anyone has any idea what might be causing the problem please let me know cus this is really starting to piss me off and I have a long highway trip planned in a few weeks. The only other thing I have done that may have affected it somehow is I have changed the speedometer cable and the speedometer gear for my gear swap. Thanks in advance for any help.
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1988 Mustang GT - 331, hand ported Twisted Wedge heads, TFS Stage 2 cam, R-Series intake, 1 3/4 long tubes, dual 3" exhaust, tko 600, Zex 100 shot, ect.
357 rwhp/ 361 rwtq on motor
428 rwhp/ 484 rwtq on 100 shot
12.48 @ 111 mph on motor (2200ft + elevation)
11.7 @ 120 mph on 100 shot (2200ft + elevation)
If it only does it when the Cruise is set, it could be a vacuum leak. Hopefully from a hose, and not the vacuum motor. Its vacuum source is the vacuum tee (log?) on the driver side of the firewall. It should be the line hooked to the port labeled "SC".
The vacuum motor/control unit is behind the driver side 5.0 badge. Remove the inner fender liner for access.
Also check the linkage from the vacuum motor to the throttle.
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1992 Deep Emerald Green Mustang GT Hatch, 5 speed, 2.73s, Mac fenderwell cold air intake, '93 Cobra MAF, Mac 70mm throttle body & spacer, Explorer intakes, Mac unequal headers & offroad pipe, Magnaflow catback, Walbro 110lph fuel pump, Jet adjustable FPR, MSD Blaster coil, Accel 8mm wires, FRPP aluminum quadrant, UPR firewall adjuster, stock cable, Granatelli upper control arms.
Waiting to go on: Granatelli lower control arms, and GT40 Iron heads!
If it only does it when the Cruise is set, it could be a vacuum leak. Hopefully from a hose, and not the vacuum motor. Its vacuum source is the vacuum tee (log?) on the driver side of the firewall. It should be the line hooked to the port labeled "SC".
The vacuum motor/control unit is behind the driver side 5.0 badge. Remove the inner fender liner for access.
Also check the linkage from the vacuum motor to the throttle.
Thanks for the reply, was not even thinking about the vacuum line and all of that. I checked over the hose that goes from sc on the tree to the inside of the car and it looks to be in good shape, no small cracks or nothing. With the cable that goes to the TB, does it matter what notch on the end of the cable is used in the connector? The last time I took my upper intake off I took the metal clip off of the line and took it out of the plastic holder and did not know which of the few notches the clip was in on the end of the cable when I went to put it back on so I put it on the very end notch, would that cause any problems?
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1988 Mustang GT - 331, hand ported Twisted Wedge heads, TFS Stage 2 cam, R-Series intake, 1 3/4 long tubes, dual 3" exhaust, tko 600, Zex 100 shot, ect.
357 rwhp/ 361 rwtq on motor
428 rwhp/ 484 rwtq on 100 shot
12.48 @ 111 mph on motor (2200ft + elevation)
11.7 @ 120 mph on 100 shot (2200ft + elevation)
does it matter what notch on the end of the cable is used in the connector? The last time I took my upper intake off I took the metal clip off of the line and took it out of the plastic holder and did not know which of the few notches the clip was in on the end of the cable when I went to put it back on so I put it on the very end notch, would that cause any problems?
I looked at mine, but couldn't really see the cable, and I've never separated the CC cable from the throttle cable.
I would probably try the next notch, and see if it improves.
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1992 Deep Emerald Green Mustang GT Hatch, 5 speed, 2.73s, Mac fenderwell cold air intake, '93 Cobra MAF, Mac 70mm throttle body & spacer, Explorer intakes, Mac unequal headers & offroad pipe, Magnaflow catback, Walbro 110lph fuel pump, Jet adjustable FPR, MSD Blaster coil, Accel 8mm wires, FRPP aluminum quadrant, UPR firewall adjuster, stock cable, Granatelli upper control arms.
Waiting to go on: Granatelli lower control arms, and GT40 Iron heads!
when i had my 89 gt it did that surging when cruise was on . ended up being the vacuum/motor pod like he said above. i just unhooked it. sucks when your on cruise and have a ricer mess with you while your crusin and have to kick it off and downshift for a flyby
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84 Predator Mustang GT302R [Gone]
89GT: built fairly good (sold)
92LX: 4cyl to 5.0 conv. completed on the cheap (sold)
88GT: 302/AOD,stock 2.73's and traclok, LT's, custom 2 1/2" exhaust made by me with thrush chambered mufflers dumped at rear axle, hayden electric fan..more to come, daily driver.
Cruise Control surging/intermittent 
