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Thread: Returning to idle problem

  1. #1

    Default Returning to idle problem

    So I've got a 1990 Wolfsburg Jetta with the common 1.8L and when the engine idles down (pushing in clutch coming to a stop or just revving engine and letting it return to idle) RPMs drop to about 500 and the car acts like it will stall then the RPMs quickly pick back up to normal (around 1000). With the tired battery it came with it actually did stall (on the freeway!) but with a new battery it manages to stay alive.

    I haven't had this car long but it has always done this for the 6 months I've owned it. Like all good Volkswagens it has many miles on it (the car stopped counting at 145,000 miles years ago). I've suspected a vacuum leak and replaced obviously cracked hoses. I know the coolant sensor to the gauge isn't working, whether that matters? Other sensors at fault?

    I'm stuck, thanks for any help. :-)

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  3. #2
    Senior Member dbaseballs is on a distinguished road dbaseballs's Avatar
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    Default Re: Returning to idle problem

    throttle positioning sensor, underneath the throttle body, or maybe the IAC? i think its called the idle air control valve its in front of the throttle body, controls the idle, could be either one could be both

  4. #3
    AllShoNoGo Gargamelmk2 is on a distinguished road Gargamelmk2's Avatar
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    Default Re: Returning to idle problem

    Could also worse case senario be your ECU...I'd lean more towards suspecting the idle air control valve (IAC) of malfunctioning. The IAC controls the air that goes into the cylinders. When you push the pedal, you are not doing anything to actually put more fuel in, rather, you open the air valve letting more air through. The IAC does this automatically for idle purposes...to keep the engine from stalling.
    clean out your IAC, it could be dirty..remove it and clean it with either throttle body cleaner or brake cleaner.
    If Nissan motorsports is called Nismo, wouldn't Honda motorsports be called Homo?

  5. #4

    Default Re: Returning to idle problem

    Clean up would be a great fix- no parts to buy! I'll give it a shot. Thanks!

  6. #5
    AllShoNoGo Gargamelmk2 is on a distinguished road Gargamelmk2's Avatar
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    Default Re: Returning to idle problem

    Also have your Alternator checked just for good measures, it may have a stuck brush..I put a used Alternator on my jetta about 4 months ago ($50) Also a brand new battery.In the past month it has been acting up very simillar to what you say..After sitting on the side of the road the other night for 3 hours waiting for my buddy with his trailor I decided to have it checked...It was "fubar"(sticky brush),paid $50 for a messed up one no better than my last, even better... a brand new Bosch Alternator was only $119
    If Nissan motorsports is called Nismo, wouldn't Honda motorsports be called Homo?

  7. #6

    Default Re: Returning to idle problem

    Check all vacuum hoses as well. The 1990 1.8 with the Digifant injection is very sensitive to vacuum leaks. A stuck PCV valve will affect it also. The PCV is quite expensive to replace. Remove & spray repeatedly with carb cleaner will usually fix.

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