Stuttering At Cruise, Can't Figure It Out!

Discussion in '1994 - 1995 Specific Tech' started by 99FiveOh, Dec 3, 2013.


  1. 99FiveOh

    99FiveOh Advanced Member

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    I just got my new engine in and it runs great except when I'm driving down the road the car will stutter when I level the throttle off from acceleration to cruise. If I'm on the gas it accelerates fine and if I go to coast and let the engine rev down as the car slows it's fine. It's only in that sweet spot between acceleration and coasting.

    I replaced O2 sensors today, no change

    I checked my voltage sweep on the TPS for any dead spots and there was nothing. I slowly tested it from .98 to 5 volts with zero dead spots.

    For giggles on the way home a little bit ago I unplugged the MAF and the stuttering stopped. Now common sense would tell a lot of people "well it must be the MAF" but no necessarily. When you unplug the MAF the computer goes into limp home mode and probably ignores a few sensors at that point and runs the car from predetermined values for whatever RPM you're running.

    So, what I'm looking for is ideas. I can't hear any hissing noises all around the motor and the intake so I don't think I have a vacuum leak. And spraying carb cleaner all over my powdercoated intake isn't my first choice as it will eat the coating!
  2. 99FiveOh

    99FiveOh Advanced Member

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    Ok, I just went out and changed the TPS and tried a known good MAF and no change. I found some frayed wires running to the TPS and fixed them, however, before discovering the wires the voltage check showed all those wires to be getting a signal without shorting out.

    Has anyone else had something similar with the F cam? This my first H/C/I car so I'm not sure what to expect. It's not tuned yet but I can't imagine that would be the issue. I though aftermarket cams just cause idle problems, not part throttle stuttering problems.
  3. 99FiveOh

    99FiveOh Advanced Member

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    I also wanted to add the stutter doesn't happen until a few minutes into the drive.
  4. revhead347

    revhead347 I have face herpes.

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    I had that problem before, and it was a bad Idle Air Controller.

    Kurt
  5. 99FiveOh

    99FiveOh Advanced Member

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    I can unplug the IAC and it still does it. When you unplug the IAC it closes completely and doesn't move.
  6. jozsefsz

    jozsefsz Active Member

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    It sounds like you might have a lean condition -- seems like you suspected that with changing the O2 sensors and checking the MAF. Your tune should take care of that. If you're reasonably confident you don't have a vacuum leak (check the major offenders like the PCV system hoses including the fresh-air intake hose by the oil filler which sometimes gets screwed up when people add a CAI), the only other thing I might think to check would be your fuel pressure especially if you have an adjustable regulator. Being off a little in fuel pressure can have a dramatic effect on coasting AFR.

    I've heard your symptoms described as "bucking" many times, if that helps your search a little.
  7. 99FiveOh

    99FiveOh Advanced Member

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    The pcv system is deleted and I run a breather in the oil filler. The hose running to my vacuum tree is the only main hose coming off the intake aside from the little FPR hose. Also it's a stock FPR. I really thought the F cam would play nice with the computer. The idle is good, it doesn't hunt for idle when I stop or anything. It almost feels like a miss when I level off the gas pedal. It didn't do this before either. It's annoying.

    By unplugging the MAF I force the car into limp home mode and the bucking stops. A different MAF had no change on the symptoms so I know the maf isn't bad. When it goes to closed loop something is happening to cause this. I don't even know what the computer could do to make it miss/buck like this aside from dumping fuel on the plugs and fouling them out. Under WOT it doesn't miss a beat though.
  8. jozsefsz

    jozsefsz Active Member

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    Under closed loop you're typically going to run a little bit leaner with a little less timing advance than the base-tables that is uses in open-loop. That's why I was drawn to a lean condition which is what had caused bucking for me in the past (only at cruise, most noticeable when letting off the throttle). You could also try mildly retarding your timing to see if that helps.
  9. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    So if a sensor is suspect, have you actually tried running the check engine codes?

    Only 13 or so of the 100 possible codes trip the CEL. I'd start there before throwing money at the problem and not being sure it's the cause
  10. 01Laser

    01Laser New Member

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    Could also be a vacuum leak!
  11. 99FiveOh

    99FiveOh Advanced Member

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    I've done some extensive ready and it seems that many have this issue with the F cam specifically and only a tune will fix it. I have a large collection of parts at my disposal to try different things and I can tell you NONE of the sensors are causing this. I have not pulled codes because I can never understand the flashing lights. They go too fast and kinda run into eachother.

    Doesn't matter anyway, I just sold the car.
  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Finding vacuum leaks

    Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed. Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Fire is an excellent hair removal agent, and no eyebrows is not cool...


    The answer to the difficulty with the flashing lights is a Equus code reader. Google Equus 3145 for the best price & delivery. Walmart may even have them for sale online for $25 price.

    Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

    Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

    Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
    Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

    [​IMG]

    [​IMG]

    If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

    [​IMG]

    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

    [​IMG]

    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


    WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

    What to expect:
    You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

    Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

    Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

    Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

    Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
    See AutoZone Part Number: 25886 , $10
    [​IMG]



    Alternate methods:
    For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

    Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader (3145. It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
    Last edited: Dec 8, 2013
  13. 99FiveOh

    99FiveOh Advanced Member

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    Sold the car but I've already seen and followed your posts before. This isn't my first rodeo so I had already checked all the possible causes. It was just in the tune with these F cams. It's a common occurrence from the research I've done.

    I've upgraded to a 96 Cobra now and lemme tell you what, I get 5.0 h/c/i power with the smooth stock 7k rpm 4 valve! I'll never go back to pushrod motors again!

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