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Limp Mode

2338 Views 5 Replies 4 Participants Last post by  pearlgolf
I Have A 2002 Jetta Tdi That Will Go Into Limp Mode .i Have Changed All Vacumm Lines With No Change.so I Unplug The Map Sensor And Now The Car Will Not Go Into Limp Mode,but On Big Hills It Is Lacking Power.does That Sound Like A Faulty Map.
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Lacking power on big hills only or at all times?

Start with the simplier stuff: injection timing, clogged fuel filter, or clogged fuel injectors. If the engine is running smoothly but it's just no power, the fuel injectors are probably good. If you are using regular diesel or retail biodiesel the fuel should be good. If you are using used grease it's possible there is a fuel pump problem or other fueling issue.

You need to do more tests to know for sure if the MAF is bad. If you unplug the MAF sensor and it's still lacking in power then there is something else that is contributing to limp mode.

Do more tests for the MAF sensor as listed here: http://www.myturbodiesel.com/1000q_how_to/a4/maf.htm

For example, another test you can do is to rev the engine in neutral close to redline. A bad MAF will not let you do so. Since your vacuum lines are new but no change, it's possible that these are contributing to your problem:

Bad N75 solenoid. This controls the turbo through the vacuum lines.

Bad VNT actuator. This is on the turbo and moves the turbo variable vanes.

Other fueling issue.

If you just had the timing belt done within the last 1500 miles then it's possible it was done incorrectly.
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It Seems To Do It All The Time On The Big Hills But Doesn't Go Into Limp Mode
Limp mode is a loss of power. It sounds like you ARE going into limp mode on the big hills. Either that or the turbo is rusted and/or seized.
I think you may have multiple issues going on. The car is designed to fall back onto safety MAF values when you unplug the MAF plug. So it should still run OK but not at it's best. Is this what you're describing?

If you notice a loss in power on the big hills vs. slow and steady driving on level roads I would say you are still in limp mode. Check fueling as well. You could have a problem at the fuel filter, fuel pickup in the fuel tank as well. These would cause an overall loss in power.
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