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Trek Jetta is stalling out.

PostPosted: Oct Tue 28, 2014 7:18 pm
by Checkers
1996 Jetta 2.0
Brand new MAF, plugs, wires, cap, rotor, air filter, battery, and fuel filter.
The Jetta has been stalling at an idle lately and it is very odd. I was able to recreate the stall today by turning on the headlights and heater fan at the same time, dropping the idle below 700 and killing the engine.

Did some research and decided to clean the throttle body. After cleaning thoroughly I noticed a slight increase in RPMs at idle, but nothing major. I was unable to stall the car again by causing a voltage drop.

Threw a voltmeter on and watched it as the car idled to a stall. No drop in voltage until the engine stalled, ruling out a voltage regulator/alternator problem. Starts with 12.5v, charges at 14+v, stalls and drops to just below 12v.

I had a few miscellaneous codes leftover from before the tune up and new MAF, so I cleared them and in about 50 miles of driving today the CEL never came back.

Sprayed down the vacuum lines and couldn't find any issues whatsoever.

The car refused to idle a few weeks ago so I replaced the MAF with a cheap one from the internet and it still threw a code so I just replaced it with a new Napa one and it corrected the problem to an extent but it's still stalling.

With the MAF unplugged last week it would run great, and now with it unplugged I can't get it to stop stalling.
Next thing to try would be the coil I guess. Anyone in Bozeman have a MK3 these days that we could swap coils on to test it?


Anyone...Bueller? Bueller? Bueller?

Re: Trek Jetta is stalling out.

PostPosted: Oct Tue 28, 2014 7:57 pm
by Mikewire
New member? What's your name son?

:laughing: Sounds an awful lot like a cracked or failing ignition coil. Hope you can source a local one...new ones run $110 or so.

Re: Trek Jetta is stalling out.

PostPosted: Oct Wed 29, 2014 5:59 am
by Reverend
would the alternator be the problem?

Re: Trek Jetta is stalling out.

PostPosted: Oct Wed 29, 2014 9:10 am
by Mikewire
Reverend wrote:would the alternator be the problem?


Could be, but it sounds like he's got proper voltage at idle if he's got 14V+.

Bypass the alternator by throwing it on a charger while testing and see if you can replicate the issue.

Re: Trek Jetta is stalling out.

PostPosted: Nov Wed 05, 2014 8:06 pm
by Checkers
Hey everyone, my name is Stoney. lmao

So I've found that by disconnecting the vacuum line that runs from the throttle body down to a control valve or sorts by the airbox that it fixes the stalling, but idles high because of the obvious vacuum leak. What is that valve and what does it do?

Trek Jetta is stalling out.

PostPosted: Nov Thu 06, 2014 7:16 am
by MT-Getto
Swapped out TB?