Rough idle after LIM and SS IC install

Hello all,

I installed a ported LIM and an SS IC this past weekend. Everything's back together now, but the car idles rough. When idling, the car shakes and feels as if it wants to stall out.

I do have an autotap scanner so I can check for anything that may help.

I also added an oil breather.

Here are the specs of the car.

98 White GTP, N* TB, 3.4 pulley, SLP headers, 1.9 Rockers, 105# springs, ZZP PCM, Flowmasters, GM performance Handling kit, FWI, GMPP springs, U bend delete, SSIC, Ported LIM, Oil breather, Autolite plugs, ported SC, 12" brake upgrade with slotted cross-drilled rotors

Thanks in advance for any assistance.

Andy

Andy, just curious, did you use the GM supercharger gaskets (2) or did you go with garlock (junk!)?

I had the Garloc but I read they were junk so I went and got two Felpro gaskets and the Felpro is what I installed.

It just threw some codes.

p0171 Fuel Trim System Lean Bank 1
p0507 idle control system RPM higher than expected

Try cleaning the idle air controller (IAC) located on the throttle body for the P0507 DTC and the seat where it mounts to the throttle body. If that doesn't work then replace it.

For the P0171 DTC (not good) check all the vacuum lines at the intake system including ones used for evaporative emissions.

DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero the PCM is reducing the amount of fuel to compensate for a rich condition.

Note: Even an issue with the IAC can set the P071 DTC.

For further diagnostics check the short and long term fuel trims with an odb-ii scanner that has the capability to check it.

With those DTC's I'm betting you have a vacuum leak around the sc/intercooler gasket area.

Just curious, the LIM is ported, did they "open it up"either a gen 3 or gen 5 supercharger? Seems I remember the gen5 opening is slid a little over than the gen 3, so if the LIM is "opened up" sort to speak, then a gen 3 gasket wont seal correctly, and you may need a gasket from a gen5.

I got some carb cleaner and sparyed around the gasket to see if the idle changed.

The gasket above and below the IC are leaking. I trimmed them to match the ported LIM and I didn't use gasket sealer.

II got some ultra gray sealer to put on it when I take it apart again.



But, the idle also changed when I spray between the LIM and head. I don't know if the card cleared is getting sucked into the leak around the IC or if the LIM gasket is also leaking. I got the aluminum framed gasket and torqued the LIM to 11 FT/lbs in the proper sequence.

I'm going to have to pull it apart again, I don't want to take the LIM off again but if it is leaking, what can I do to reseal the LIM gasket?

I got the Ported LIM from someone who got it from someone, I will try to get more info on it.

Fuel trims were higher when I scanned.

Andy

Yeah, I figured the problem was with the IC gaskets. I dont think I would yank the LIM off again, I doubt its leaking there.

Just curious, you did replace the injector o-rings, right?

I did replace the o-ring gaskets.

Another question, my old LIM had the coolant holes for the throttle body tapped and plugged, this one did not. The IC core had a black O ring that was secured to the plate with metal (looked to be part of the intercooler plate). I put a ring in the hole that had nothing and left the ring out of the side that had the o ring secured by metal. Do I need to plug these coolant holes?

Also, someone mentioned about putting a dime in the EGR hole to block it, is there any benefit to doing that?

A dime? Thats aweful spendy. My friend used a penny!

however you would also need to get an EGR blockoff plate for the exhaust manifold and delete all the EGR codes in your PCM.

I am not exactly sure about your t-body coolant passage issues. I left all mine alone. They do require new o-rings unless you get a gen 5 gasket which I think has o-rings built in. Dont quote me on that.

I'll skip the EGR blockoff.

Tblake, do you have an intercooler installed?

I do not. Sorry.