Over time, the Intake Manifold Runner Control system (IMRC) can get varnished and gummy which will lead to poor performance. If you don’t feel like disassembling the system to clean them manually, you can try a trick with Seafoam fuel additive. If this doesn’t work, your only real alternative is disassembly and manual cleaning, which is outlined in this linked document. Give this a try if you want to save a day of labor.
- With the motor off, simply pull the PCV hose out of the DRIVER-side valve cover, but leave it connected to the manifold.
- Open the bottle of Seafoam and pour it in a shallow Tupperware container. Put the end of the PCV hose into the container. Mine didn’t reach that well so I used an extra piece of hose to be able to get there. You will want one person to hold the hose in the solution and one to get in the car to start it and then shut it off.
- Start the motor for about 12 seconds. This will allow the engine to ingest the contents of the container. When all of the fluid has been ingested, kill the engine. The faster you turn it off, the better. You may need to goose the throttle a bit to keep it running while the fluid is being taken in.
- Let the car sit for 30 minutes with the engine off.
- Make sure you are outside because this step will create a LOT of smoke. I think I made my neighborhood a little mad. Start the motor and let it idle for about 30 seconds. The engine will be sluggish and want to die, but will usually stay running if you help it out with throttle. After 30 seconds or so, raise the RPM to about 2800 and hold it there until you feel the motor start to rev more freely (usually about 20-40 seconds). This step makes lots of smoke. A LOT of smoke. That is all the dissolved carbon blowing out.
- Drive the car making sure to make some WOT blasts to clean things up. It will still smoke a bit as it burns out contaminates. You are going to feel weird driving your nice Cobra around smoking like it has no rings but it has to be done.
- Drive the car around at different speeds. You should notice the engine awaken after about 10-20 minutes of driving and your job is done. I kept driving around even after it quit smoking. I could tell it was running more freely and it just felt better. Maybe it was in my head but I don’t think so. It needed it after 75k miles.
- credit to RippinSVT (Kyle) on svtperformance.com for the basic recipe