Idle Surge ONCE AGAIN. What could it be??

[tsi1991awd]

Had the car sitting for about 4 months to do some work to it. I put in a 3 inch GM MAF, new turbo, turbo manifold, replaced TB shaft seals, put in the black top ISC instead of the 90 ISC with the built in pigtail.

ISC is fine. I blocked off the FIAV. EGR is blocked off with a plate. TPS is set to 10% via MMCD. 3" GM MAF installed. Idle Stop Switch was adjusted properly.

If I take the connector off of the Idle Speed Switch on the throttle body, the idle will be high...around 1800 or 2000ish....it doesn't surge though. When I connect it again, it surges.

If I take the connector off of the ISC itself, it still surges...nothing changes there.

What could it be? I thought there were only a couple of things that would cause idle surge like that....ISC, FIAV, EGR.....maybe it's a boost leak? But wouldn't it have to be AFTER the GM MAF to cause it to surge like that...since the MAF is after the BOV and it is reading the airflow from there? Or what??

 

[Interlock]

Why is your TPS set at 10%? It should be 0 with throttle closed...

Check that the switch is actually making contact with the throttle return spring when the throttle closes. It should contact, and close the switch circuit.

 

[tsi1991awd]

Why is your TPS set at 10%? It should be 0 with throttle closed...

Check that the switch is actually making contact with the throttle return spring when the throttle closes. It should contact, and close the switch circuit.

No, when setting the TPS via MMCD, the throttle should be at 10% when closed and 100% when open. Mine is set at 10.1% closed and 99.7% when open. That's just the way MMCD is.

Also, I set the switch again (already did this twice previously) just like I always do. Disconnect the throttle cable, unscrew the idle switch, watch for continuity then turn the switch 15/16 of a turn and tighten the locknut. I did it all the time, the switch is good, it is set properly.

 

[NOSLO2PT0]

Eliminate the lower portion of the TB altogether. Only way to make sure the car idles rock solid.

 

[RoasT BeeF]

If I take the connector off of the Idle Speed Switch on the throttle body, the idle will be high...around 1800 or 2000ish....it doesn't surge though. When I connect it again, it surges.

This basically verifies the IPS is operating correctly. The ECU waits to see a signal from the IPS (verified when throttle closes and presses on the switch) before it begins trying to control idle. When you have it connected, its trying to control idle, when you disconnect the switch it is not trying to control idle. By the idle jumping way up when you disconnect the switch it most likely means there is to much air entering the intake manifold. When this happens the ECU will temporarily cut fuel to the injectors to bring the idle down, and then re-enable them. This results in idle surge.

First, check for air leaks. The easiest way will be a boost leak test. Vacuum hoses, PCV hose, brake booster, intake manifold gasket, throttle body gasket, and the FIAV and EGT plates. Did you replace the BISS O ring? Cover the BISS hole with your thumb while the car is idling. If the idle drops, its leaking - replace the BISS O ring. Also make sure your throttle linkage is not adjusted to tight and pulling the throttle open slightly or the IPS is not physically screwed in to far and slightly opening the throttle plate.

To clarify one thing, did you install an FIAV blockoff plate or an FIAV bypass plate? If you used a block off, you effictively eliminated the use of your ISC as it blocks off everything. Whereas a bypass plate blocks off only the FIAV but not the passage to the ISC.

 

[tsi1991awd]

First, check for air leaks. The easiest way will be a boost leak test. Vacuum hoses, PCV hose, brake booster, intake manifold gasket, throttle body gasket, and the FIAV and EGT plates. Did you replace the BISS O ring? Cover the BISS hole with your thumb while the car is idling. If the idle drops, its leaking - replace the BISS O ring. Also make sure your throttle linkage is not adjusted to tight and pulling the throttle open slightly or the IPS is not physically screwed in to far and slightly opening the throttle plate.

To clarify one thing, did you install an FIAV blockoff plate or an FIAV bypass plate? If you used a block off, you effictively eliminated the use of your ISC as it blocks off everything. Whereas a bypass plate blocks off only the FIAV but not the passage to the ISC.

When I changed out the TB shaft seals, I replaced the BISS screw and O-ring with brand new parts from the dealer. I also blocked off the FIAV. I have a 1990 TB so there is no block off plate. I had to block off a portion of the TB with JB Weld (this has been discussed many times here on Tuners)

The throttle cable is adjusted properly and it was even disconnected and the idle was still surging.

Also, I have the MAFT set for 450cc injectors and the rest of it is zero'd out....would this cause a problem? It's set at 450cc injectors because I have an eprom chip and SAFC (which is also zero'd out)