Originally Posted by jfoj
The DISA O-ring leak seals up quickly due the quick expansion of the plastic parts and is a very small, but devastating vacuum leak for cold starts. Although I recommend the DISA O-ring be replaced, some cars will need a NEW DISA as well, but the O-ring will help any DISA valve regardless of overall condition.
Also the other thing that happens is with carbon build up on the intake valves, it acts as a sponge and absorbs fuel during the initial start up. Just like a sponge, once is it wet, it will not absorb more fuel. So with a partial vacuum leak and carbon build up you will have a lean misfire for a short period during cold start up. Once the car has run for a short period, or is turned of and restated withing the first few minutes the fuel cut off is bypassed. Once the fuel cut off is bypassed or reset, then the engine will no longer misfire like the engine is going to fall out of the car!
So the DISA vacuum leak usually impacts the center cylinders more so than than cylinder 1 & 6. If you remove the DISA for inspection and do not replace the O-ring you have just made your problems worse!
Another possibility is the vacuum control hose (both rubber and hard plastic hose) that connects to the SAP check valve. This SAP check valve vacuum hose only has vacuum for the first 90 seconds during cold engine start up. A smoke test will not pick up this SAP vacuum hose as there is an electric solenoid under the intake that is closed except for during cold start up for the first 90 seconds. The way to check this hose with a smoke test is to disconnect the vacuum hose as the SAP check valve and "backfeed" this hose. The other very easy test is to disconnect the vacuum line at the SAP check value and just put a hand vacuum pump on the connection and see if you can hold a vacuum in this short section of line, if not, you have a problem with this 3 foot section. You could also try to block down this line with your mouth, you may need an extension on the end so you can get your mouth on this hose.
Everyone needs to leave the expensive/hard part replacement for last. You are wasting you time, money and effort replacing expensive hard parts if you have not addressed the rubber parts. The rubber on these car is all failing as it is at least 6+ years old and is hard, dried out and oil soak.
Quit screwing around, re-read my link, spend not more than $50 and get your current problems solved. But keep in mind, you will probably need to do more maintenance and replace other rubber parts to really head off your problems.
You really need to replace all the rubber and plastic parts connecting to the intake and crankcase on these cars. This includes the entire CCV system, intake elbow, ICV hoses, SAP vacuum lines and pressure hose, dip stick o-rings, vacuum caps and probably the entire DISA to really keep your car in top notch and basically vacuum leak problem free for another 6+ years. If you are smart you will do this one time and your cold start headache will be gone for a long time. You can do all of this for less than the cost of MAF, spark plugs, coils, O2 sensors and all the typical hard parts people replace first!
Also do not forget what your cooling system is made of, plastic and rubber, same rules apply here but this is a totally different discussion!