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Subject Idle Troubleshooting - 90 TT
     
Posted by fantomZ(OH) on June 17, 2022 at 3:01 PM
  This message has been viewed 297 times.
     
     
Message I've been slowly working against fluctuating idle (surging upwards, then downwards) in my 90TT, searching the archives, reading a bunch, removing cleaning and checking the IACV, checking for vacuum leaks (none), verified fuel pressure is good, testing coolant sensor (also good) but have yet to solve the root issue.

The situation:
At idle, when cold or warm, the idle will not hold. It fluctuates or surges upwards, then downwards to the point it will almost or sometimes stall. Once the car comes off idle, driving performance is unaffected. When coming to a stop or returning to idle, the problem persists.

See YouTube video for idle


Troubleshooting:
As mentioned above, I've been researching curing erratic idle and I believe have been through several of the basics and haven't seen an improvement yet.

Through exploration, I identified that introducing a slight vacuum leak in the balance tube by removing my boost gauge off the small port on the passenger side instantly cures the issue and the car idles smoothly.

Additional Info:
The car has been in and out of storage for the last few years (kids, house, work, life etc..) but has had fuel stabilizer, full-tank and somewhat regular start-ups routinely. It's also had fresh fuel and some injector cleaner run through it (which I don't believe did anything except turn my 9.99 into exhaust gas).

There's still a few more things on my to do list but I don't get a ton of wrenching time in these days (kids, house, work, life etc...) so I was hoping I might get a hand in narrowing my focus. Any thoughts on what to try next would be appreciated!

     
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