random idle surging

[nctalon92]

Ok so Im having random idle surging on my 92 tsi. It starts surging at random times but sometimes I can get rid of it by shutting off my car and starting it up again. I did some research on it and I realize it could be a bad iac. I don't have a dvom to test it but I heard that some people unplug it and it stabilizes the idle so I unplugged my when it started surging and it did nothing. Could the iac still be the problem or does that mean its something else. Also ever since it started the idle surge problem it seems like I've lost power in first gear. Just doesn't accelerate like it used to in first gear even when the idle isn't surging. Any ideas?

 

[pj91gsx]

my friends 92 TSi replaced his fuel filter and the idle surge stopped. Does you car throw a CEL? Yes a bad IAC will cause idle surging but will probably throw a cel.

 

[Boost92awd]

Try looking for something basic, such as a loose throttle cable, first. Other sources of idle problems include fouled spark plugs, a defective or gunked-up idle speed control (ISC) motor, leaking injectors, a cracked vacuum hose, or a damaged intake manifold gasket. High idle can also be caused by a throttle cable or cruise control cables that are too tight.

Some troubleshooting tips: if your idle adjusts when your A/C compressor is on, or when all of the electrical accessories are on, the ISC is at least partially working. If your idle appears to fluctuate with temperature, suspect an air leak in a vacuum hose or at the air intake first.

If you need to check the ISC, do it when it is hot. The ISC resistance can sometimes change when it has cooled down. Thus, the ISC looks ok when checked, but misbehaves when actually operating. The same holds true for cables since they can tighten up during operation.

The pins will look like this

1 2 3

4 5 6

There are six pins on the ISC. They are labeled 1 2 3 across the top and 4 5 6 across the bottom.

Measure the Resistance between pin's 1-2, 2-3, 4-5, and 5-6
Each pair of pins measured should read 28-33 Ohms
Note: The values should measured with the car off and cool!
If any of the "coils" (which is what you're testing) are bad then your ISC needs to be replaced
If all the coils were good there's one other thing to check on the ISC


Use a 6volt battery (lantern or camera battery) and apply 6 volts to the ISC motor.
Use jumper wires to connect the positive (+) terminal of the battery to terminals 2 and 5 of the ISC and the negative battery terminal to terminals 3 and 6 of the ISC.
If there is no movement or vibration from the motor, then it is bad
Note: The use of a 12volt battery will destroy the ISC motor!!

 

[pj91gsx]

check you ignition timing. It should be 5 degrees advanced. And new ngk plugs would be nice too.

 

[nctalon92]

Ok so I borrowed my friends dvom and tested the ISC and its bad. The 2-3 coil had only 1ohm of resistance. so that is the reason the idle is surging but why does it feel like I'm losing power. Could the ISC cause the engine to run rich? Also what could I expect to pay for a used ISC?

 

[pj91gsx]

Idk if the isc would cause a power loss, but Im pretty sure it will cause you to run rich. You will just have to see if you get your power back after replacing the ISC. I would recommend a boost leak test if you still have a power loss after replacing the ISC.

 

[Boost92awd]

I wouldnt suggest buying used sensors.

 

[pj91gsx]

when push comes to shove you have to do what you have to do with you budget. I would never buy a used oxygen sensor. but I know the ISC is about 200 dollars I think. I would rather keep buy 8 used ones for 25 a piece. than pay 200 for one.

 

[nctalon92]

Well I know a new one is at least $200 and if I can get a perfectly good used one for an 1/8th the price of a new one then why the hell not.

 

[pj91gsx]

see what you can find in classifieds. ebay has them for 40 for the lowest. I think you could probably find one a lot cheaper than 40.

 

[viprez586]

Idk if the isc would cause a power loss, but Im pretty sure it will cause you to run rich. You will just have to see if you get your power back after replacing the ISC.

WTF Last time I checked, when I forced a rich condition I lost performance.


Anyway to the OP: When you replace your ISC make sure you clean the passage way to get any carbon build up out of the passage. Also make sure you have a new O-ring to properly seal it. Lastly I don't know about yours, but the screws holding my ISC on to the TB are fairly tight and you might have to use one of those drills that give an impact to the bit while turning.
Or use a 1/4" or 3/8" impact gun on low torque. Key idea here is not to strip the screws.

 

[pj91gsx]

WTF Last time I checked, when I forced a rich condition I lost performance.


I didnt want to give any false information. I have never been in a rich condition. I have never driven my car more than 25 miles in total. I have had a hard time with dsms, but it was my fault why I had the problems I did and still do.

 

[pj91gsx]

WTF Last time I checked, when I forced a rich condition I lost performance.

I didnt want to give any false information. I have never been in a rich condition. I have never driven my car more than 25 miles in total. I have had a hard time with dsms, but it was my fault why I had the problems I did and still do. I don't even know what kind of power I will feel when I actually get my motor together again.

 

[viprez586]

well that sucks.

Just wanted to clear the air with the rich and performance thing there.

G'luck getting it running again, after that then you have the fun of finding out how to make it run nice and tune it...thats even more fun until you're making some power without blowing things up.

 

[pj91gsx]

Thanks. I hope I will get it running this summer. I have had it for almost 2 years now. I bought a jdm swap and ruined it. It was such a disaster. I pulled the motor because I realize all of the terrible things I did to the motor. Not having an oil cooler and having gas in the oil, because of the car not starting. Then taking my car out for a run and not knowing that the boost controller soliniod was hooked up wrong. The boost gauge hit 35lbs with my 16g, and I also had a boost leak. I would have mine running I just worked on my car and not my friends cars all the time.

 

[GirlDriver]

Kind of back to the original post issue, my 91 has some sort of vacuum leak. When I turn on the A/C, the surging stops. I would like to replace ALL of the hoses under the hood because the car has been sitting a while and I can see a few of them are dry-rotted. I need to know what to focus on first that might get rid of this surging and are there any recommendations for hose replacements?

 

[pj91gsx]

Idle air control valve was his problem,