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Lincoln Forum: Sudden acceleration
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  1. #1
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    Sudden acceleration

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    My 94 TV has 83k actual miles. Recently has begun an occasional moaning sound. Within a few minutes it will accelerate on its own. Braking works, the engine slows, and I do not lose control. What could be happening?

  2. #2
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    That is strange, haven't had any experience with this issue though.

  3. #3
    Town's Avatar
    Town is offline Senior Member My Lincoln(s): 2017 Lincoln Continental Reserve 2.7 AWD
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    Quote Originally Posted by Nilla View Post
    My 94 TV has 83k actual miles. Recently has begun an occasional moaning sound. Within a few minutes it will accelerate on its own. Braking works, the engine slows, and I do not lose control. What could be happening?
    I assume you are talking about your 94 Town Car? The moaning may be from the "hooter hose" or the IAC and the unintended acceleration from the IAC (idle air control valve) or a carpet able to move over the throttle pedal. The IAC controls idle speed and is the most likely cause of your 2 problems. Do not buy an aftermarket IAC, they do not work properly because of alignment issues, pay the extra and get a genuine Ford part.

    Good luck.

  4. #4
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    Thank you for your very helpful reply. I wish it were only a carpet issue. This morning the shop did a test and got 172 and 176 codes with "no explanation." He said some codes are proprietary, and this is not a dealer's facility, so he doesn't know what they mean. Would these indicate the IAC? Now they want to test each cylinder and other things for a vacuum problem, but are not mentioning the IAC. Would the IAC show up in that? They have done good work here before and saved me money over the local dealership, but this isn't making sense to me. One friend mentioned changing the fuel filter. Probably time for that, but it doesn't seem right. I really appreciate your input!

  5. #5
    Slick Fan's Avatar
    Slick Fan is offline Senior Member My Lincoln(s): 2003 TC Signature, 1977 TC, 2003 Aviator
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    I wonder if the cruise control is somehow arming itself & accelerating to some preset speed? I've never had a car arm it's CC like that, but who knows? It sounds like the car returns to normal once you apply the brakes, which leads me to wonder about the cruise.

  6. #6
    driller is offline Senior Member My Lincoln(s): 2010 Limited Edition Navigator L, 2006 Designer Series Town Car, '98-'96-'93 Mark VIII's
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    I'm not 100% sure about how they got the codes, but they should be EEC-IV codes?

    172 - Lambda sensor (right) too lean
    176 - Lambda sensor (left) too lean

    To me that points to an air leak between the throttle and MAF sensor causing unmetered air to enter the intake causing a lean air/fuel mixture.

    That in itself should not cause any acceleration however.

    If it were mine, I would clean the MAF, recheck the air intake tract and look for any source of possible leaks, including broken vacuum lines. If that doesn't cure the issue, I would also replace the Idle Air Control Valve. Yes, pay more for true OEM part from a dealer. I've had too many issues with parts store brand name replacements and even so-called "Motorcraft" parts from non-dealer sources. There's far too many counterfeit parts in the wholesale market that find their way in the supply chain of auto parts stores.

  7. #7
    Town's Avatar
    Town is offline Senior Member My Lincoln(s): 2017 Lincoln Continental Reserve 2.7 AWD
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    The 172 code is likely an OBD2 code which would be P0172 that is "System too rich bank 1". The 176 code in the OBD2 system would be P0176 that is "Fuel composition sensor circuit malfunction". The standard OBD2 codes have a 0 after the P (powertrain) while the manufacturer codes have a digit other than 0 as the first. Doesn't sound like those codes are related to your problem. Does your engine idle smoothly or a bit eratically.

    Usually vacuum leaks are continuous and result in higher than normal engine speeds, but yours is intermittent. The IAC accumulates carbon from the intake and becomes sticky and usually emits a noise and keeps the engine idle speed high. The IAC could potentially increase engine speed enough (without a vacuum leak) to drive the car since the internal carbon saturated valve is moving to maintain engine speed, but it is only a guess. Cleaning usually damages the internal seals so the problem returns worse than ever. To cure the noise and potential sticky operation you would need to replace the IAC with Ford's original part.

    In addition to the already identified sources of vacuum leak, check for vacuum leaks at the hoses carrying fuel or oil. The PCV hoses often get cracks and leak, the fuel purge line from the intake to the fuel purge line (to vaccuum out the fuel tank and system when needed) are the two that are most likely to leak.

    Good luck.

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