FAST Idle

I have a 88 Jetta 1.8 engien, I believe it has a digifan fuel injection system. These two problems stated almos at the same time (within a week) so I don't know if they are related. Here are the problems:

  1. When the gas tank is about 1/3 full, the car acts like is running out of gas. It starts to jerk ans stalls. So I have to make sure the car has at least 1/2 of gas in the tank.
  2. This happens regarless. It Idles to fast. When cold it idles over 3 on the scale (normaly used to be .9) and when worm it idles at 1.8

Like I said, this two problesm stated this winter within a week.

Any help will do...

-Cesar.

Reply to
Cesar
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That generation Golf / Jetta is notorious for eating through transfer fuel pumps. This is the one located inside the gas tank. I have had several of these go bad. Usually they start making a horrible buzzing sound, letting you know it is time for a replacement. The last time it happened it died quietly. With a full tank of gas the car would still run on flat ground, but would stutter going up hills or at high speed. If you have the Bentley for your car it describes how to test and replace the pump. It is an easy job, but refrain from smoking... Last time I did it it took me and my brother less than 30 minutes to test and replace the pump. When the transfer pump is bad the main pump (under the car) is starved for fuel, and will eventually fail too, so test, and if necessary replace, the transfer pump ASAP.

I am not familiar with digifant, as my car has CIS-e. I had a problem with high idle speed last week and found the problem to be one of the throttle position switches. I believe digifant uses a throttle position sensor instead of the switches. There are some digifant gurus in this NG, so I'm sure you'll get better info from them.

Is your spell checker broken?

Cesar wrote:

Reply to
Randolph

I agree on the transfer pump. My '91 GTI would stumble quite a bit and act as if it was out of gas if I didn't have at least 1/4 tank in it. Sometime it'd be accompanied by a louder-than-usual buzz (but still not that loud) from the fuel pump.

Order a new transfer fuel pump and make sure it's Pierburg. VDO made the original one and that's the one that tends to fail.

The transfer pump is part of the fuel sender assembly. Either under the back seat or under the trunk carpet (not sure on a Jetta ''cause I have a GTI, but I think it'd be in the trunk) there's an access panel. The Bentley says to have less than 3/4 tank when you do this but I prefer to have as little as reasonably possible. Remove the panel and then you'll see the pump assembly. Start the car and pull the fuel pump fuse and let the car run until it dies. Sometimes it's a few seconds, other times it's a minute or two. This is to remove as much fuel from the lines and also to not have power to the pump either in case of a spark (the Bentley says to disconnect the negative battery cable but I just pulled the fuse and figure that was enough...YMMV). After it dies, turn off the key so the ignition isn't on. Remove the wiring connector from the top of the assembly and remove the hoses (but remember which goes where) and if the clamps are original, they'll be destroyed in the process (you will need new clamps). Twist off the lock ring and carefully pull the unit out of the tank Swap out the pump portion from the unit, reinstall, connect hoses with new clamps, connect wiring connector, replace fuse, start car, check for leaks (if none, install cover plate), you're done.

Digifant II uses idle and full throttle switches. Digifant I (only found on California-spec gas 8V engines for 1991-1992) uses a throttle valve potentiometer instead of the switches.

The switches are located in back or under the throttle body according to the Bentley. I've never seen them myself because I have a Digifant 1 car though but that's where they should be. I guess make sure they're clean and operating OK.

Also check the coolant temperature sensor. On later Digifant cars it's one of two sensors on a water outlet coming out of the head between cylinders 3 and 4. Older Digifant cars are a little different but it's somewhere in the same area. If the sensor is bad it'll be sending wrong info to the ECU and the ECU will think the engine is colder than it is and it will make the car run too rich and idle too fast. The sensor is usually pretty inexpensive to replace. Just replace it when the engine is cold so as to not lose too much coolant. When you buy the sensor, get a new o-ring too.

The best place for "Digifant for Dummies" is Ken's Digifant page:

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Reply to
Matt B.

The bucking problem is likely ignition wires. Gently mist them with water on a dark evening and look for sparking. If you see any, replace them.

Other things... bad grounds, the main culpret is usually a broken wire at the driver's side rear of the valve cover.

Could also be a vacuum leak.

Could also be either the cam timing ignition timing (or both) is off.

Check these things in order listed above (i.e. free and easy checks first)

Bob

Reply to
Bob Hetzel

I've noticed that over the last week or so, sometimes when I come to a stop, the engine slows down (90 Jetta 1.8 Automatic) and almost stalls, then it speeds itself up again to about 1100 RPM....could this be a bad ground?

Thanks,.

Pete

Reply to
Pete Cressman

Reply to
Bob Hetzel

Fast idle more that likely a timing issue, try moving the distributer to slow it down, you might have had a belt jump.

Reply to
Mustangbrad

That's about the worst advice I could think of. Do not change the ignition timing w/o knowing what you're doing. Get a timing light and check it, then set it if it's wrong. If you've never done one by ear don't start with a car with computer controlled fuel injection.

Digifant fuel >Fast idle more that likely a timing issue, try moving the distributer to

Reply to
Bob Hetzel

Thanks to everyone for your input. I have replace the transfer fuel pump and that took care of one problem. Thanks again.

The other problem (Fast Idle) still continues. Here is what I did and did not work. With the engine running I disconnected the thermo time switch and that brought the idle back to normal, so I thought, "here is my faulty sensor". I took over a week to get the right part and when I replace it guess what. It did not work.

So I am back with the same dilemma. What is causing the fast idle? If is not the thermo time switch, then is has to be something connected to it I must think.

-Cesar.

Reply to
Cesar

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