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2G Idle surge

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mcubed45

Proven Member
52
11
Mar 8, 2013
Honolulu, Hawaii
Hi guys,

So I picked up a 95 TSi awd (w/ eclipse conversion) awhile back as a project car. The previous owner did a great hack-job with electrical-taped after market gauges, a turbo-timer, etc so I'm in the process of just getting the car up and running smoothly. He also did an A/C delete and mangled the front rad support.

Initially it had a no-crank problem. Starter was good, found a loose signal wire, and ultimately found that the starter relay crapped out. Bypassed the starter relay and now it fires up 100% of the time. Yay!

Next issue was idle. It would bog at start up and require throttle to keep from dying. Upon acceleration it would often die after shifting.

Checked the ISC and found the plunger was cracked in half and missing a chunk. Replaced with new ISC and then started great but would idle at 2.5-3k.

Check BISS and found it backed all the way out. Closed BISS, then opened 2 full turns. Idling at 1.5k.

Checked TPS and found smooth readings throughout throttle range but reading 2-3% at closed throttle. Checked SAS and found throttle partially open. Adjusted SAS per FSM (first contact + 1.25 turns), but still showed IPS with no continuity at closed throttle. Removed throttle body to adjust TPS (after figuring out I still couldn't access IPS by removing fuel rail). TPS calibrated (using folded paper method + DMM). TPS/TB reinstalled. TPS now functions correctly, IPS shows continuity at closed throttle, and I get appropriate throttle readings with my OBDII scanner.

However, my idle now surges between 1.3-1.8k in a rhythmic fashion every second or so..

I found this guide and I'm inclined to think that's what's going on now...
http://www.dsm.org/how-tos/tttt/tttt3.html

The engine wiring harness is a horrible electrical-taped mess so I'm still discerning what goes where, what's OEM, and what needs to be fixed. There is an o2 sensor installed in the upstream location with the wires completely cut off. I also found what I think is the upstream o2 sensor plug near the driver's headlight (connected to nothing).

Would a missing upstream sensor cause the idle surge as described in Terry's guide? A new O2 sensor is on it's way from Amazon but I'd like to know if there's anything else I need to look for aside from vac/boost leaks. I think all the whack calibration was the previous owners attempt to get a semi-decent idle with a broken ISC and missing O2 sensor, but who knows...

Sorry for the long post. I had a 2g 420a for 15+ years but this is my first 4g63. Any advice would be greatly appreciated. TIA!
 
Last edited:
FIAV present or no? Does the idle level off at any time?
No 02 sensor upstream may be the issue if it's truly gone, as there's no info for the car to read off of.

FIAV is present and wasn't messed with as far as I can tell.

Idle constantly surges until I open the throttle. It will hold a constant RPM with throttle open. Upon closing throttle, surging immediately resumes.

No error codes either btw.
 
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