Feels like fuel cut but it's not...what is it?

[TurboDreamzGST]

I've got a 98 GST spyder, big evo3 16g, Megan racing 02 housing, custom 3" cat back exhaust, Dejon intake, GReddy type rs bov recirculated, apexi safc and boost gauge. I'll be cruising on the highway and when I get on it, the car will take off nicely and spool nicely but as soon as I let off the gas the car feels like it slams to a quick stop for a second n falls on it's face but than recovers n cruises along again. I replaced all my motor mounts so I kno that's not the reason why I feel this slamming sensation but it almost feels like the same feeling as when you hit fuel cut. Also this only happens when the car is boosting and than I let off the gas, it does not happen if I'm cruising but not boosting and let off the gas. I loosened my BOV thinking that my the turbo may have been surging but that didn't help at all. I have no CEL and no codes being thrown. What can this be? Please help!

 

[TurboDreamzGST]

Anyone? Any info is appreciated

 

[SharonTampons]

What mechanical and or electrical modifications/maintenance have you recently done?


I would start with, is a simple boost leak test. Your problem does not sound like a typical issue related with a boost leak, but it is good practice anyhow.


But the first thing that comes to mind is your ISC (Idle Speed Control valve)

>>CLICK<<
good information about the symptoms, testing and replacement.

Let's talk about symptoms:

* When you are coming to a stop and push the clutch in and let off the gas does your Idle Drop Below 750 and almost stall (or stall)?
* When you turn on your A/C does your car "Idle up" or does it go down?
* Just a general Bad Idle? (not missing but just bad control of the Idle)
* If you are having an Idle surge problem and the below steps find that the ISC is Good, please check out Terry's Troubleshooting page on Idle Surge

If you have any of the above symptoms you MAY have a Bad ISC. I am going to show you where it is (ISC) and how to test it. You will only need your hands and a Multimeter to test it.


The ISC is located underneath the Throttle Body, on the back side.

Testing this thing!
This is a pretty simple process:

* Remove the connector to the ISC


There are six pins on the ISC. They are labeled 1 2 3 across the top and 4 5 6 across the bottom. (see left)
+ 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!!

Now that you know that your ISC is bad, you need to find one! Start calling around at the local junk yards. The ISC for the 2.0L engines are all the same for Turbo or Non-Turbo cars. I have a 92AWD and I'm using an ISC off of a 93 Non-turbo and it's working great!
Getting this thing off


This is a very simple task...
+ There are two screws that hold your ISC on (an 8mm socket works great)
+ Remove the screws and pull it off
+ Be careful, there's a little rubber O-ring that can fall out

Is it Repairable?


This I'm not sure about yet. I had to break the plastic on my old one to get it apart because of a screw that wouldn't come out! I could have drilled it out but it was broken already so I wasn't too worried about it. Here's what I found, inside there are quite a few pieces, two of which seem to be the problem with these things. There are two coils inside which are soldered to the pins on the outer (brown plastic) piece. Each coil actually contains two individual windings. When looking at the coil it's covered in plastic and has three connections on it. The one on the left to the center should read around 25-30 Ohms and the same goes for the center to the right. I think if I could have gotten the plastic off without breaking it I could have replaced the bad coil (this is assuming I could have found a donor ISC to remove a good coil from). Now If I can find a broken (half broken that is) ISC I will try to repair it with my one good coil out of my original ISC. Will this work? I don't know, but if it does I'll post it you can bet!

 

[dees75z]

I know this is a long shot, but I had this EXACT problem and in ended up being the sock on the fuel pump was getting clogged from the nasty sediment that was in the gas tank. I know its a long shot but its what it sounds like to me man

 

[TurboDreamzGST]

Thanks guys!! Boost leak test checked out ok and I have had some idle issues for about 2 months now so the ISC may be the culprit...I'm also gonna run some fuel injector cleaner thru it n see if that may help at all too...any other suggestions? Might as well try anything at this point...it's all worth a shot