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1990 Talon TSI -- Idle Problems


Fubar231

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So i have a 1990 talon tsi and its been having this idle issue since i got it. Even when it gets to operating temp, it will still idle like its a cold start, or sometimes will randomly bounce between 1400-1000-1400-1000. A lot of the time it just idles high like its cold and wont drop down and surge unless i rev it up and let it idle down.

 

 

Heres a video of it (Sorry about the music, wasnt thinking when i took the video as i just pulled in my driveway from work and it was doing it)

 

http://s50.photobucket.com/user/SevereSarz/media/20130326_171653_zps42351586.mp4.html

 

What do you guys think? IAC motor? I was told it could be the coolant temp sensor... But any ideas where to start? I need to go measure the resistance on the IAC and see if its good or bad. Also theres no CELs.

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Here... let me google that for you....

 

http://www.vfaq.com/index-main.html

 

If you go to intake>throttle body you would find the article below as well as articles detailing cleaning the TB, setting the idle set screw, etc.

 

http://www.dsm.org/how-tos/tttt/tttt3.html

 

But really I think this can in theory happen on any car, unless new cars have some way to detect this situation and not go into a loop.

 

The car is cold so the idle should be high, no problem.

 

The car gets warm and it should be low.

But the idle is still high (somehow too much air getting past the throttle).

So the car cuts fuel to try to match target idle.

But the the o2 sensor sees that the car is lean.

So the FI ecu adds fuel.

But the the idel is too high.

So the car cuts fuel to try to match target idle.

So on and so forth.

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I would check these items:

Throttle Body

Idle Air Control (IAC) Motor <---this being the most common issue

Automatic Idle Speed (AIS) Control Motor

Intake Manifold

Vacuum Leak

 

Tests/Procedures:

1. Check the resistance of the Automatic Idle Speed (AIS) motor windings. Check the resistance from the center pin of a row of three pins to the pins on each side of it. All four windings should be 30-40 ohms.

 

2. Check the Throttle Position Sensor (TPS) voltage at closed throttle. It should be about 0.5 volts. Adjust by turning the throttle stop screw.

 

3. Turn the key off.

 

4. Ground pin 10 in the Data Link Connector (DLC).

 

5. Start the engine and set idle speed to about 700 RPM by turning the air bypass screw at the top of the throttle body.

 

6. Shut the engine off.

 

7. Remove the jumper from pin 10.

 

8. Start the engine and let it idle for at least 10 minutes.

 

9. If it is still idling too fast, check the secondary air valve for sticking.

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