View Full Version : questions about idle

04-03-2003, 06:15 PM
i have searched all the idle problem post and none seem to address the problem i am having so i thought to post a new one. I just have the 3.8 supercharged engine in my 89 cougar rebuilt. and since i have gotten it back i have been having a idle problem. The engine runs great but the idle jumps from 900 rpms to 1200 rpms the drops to 600rpms and it does this over and over at the same time the boost goes from 20psi vac to 18 psi vac the drops to almost 24psi vac. This is also in combo with the fact that at normal driving the boost gauge reads 20-18 psi vac, and the most i can get out it at full throttle is 5 psi boost. I know checking the maf, and iac are in order is there anything else that could be the culprit of this problem?

04-03-2003, 08:56 PM
You have an air leak somewhere after the MAF. You can't find it by look and feel, you need to have the engine running and spray propane or other combutable like intake cleaner at each of your intake connections and vacuum lines/connections. If the idle changes as you spray, stop and fix it, then start again until you find and seal them all. Good luck

04-03-2003, 10:34 PM
Make sure you check your collar nut. (The big not looking thing connecting the top of your supercharger to your intercooler tubes) That piece, if not properly torqued, will come loose on you. Mine did and and I had very similar problems. Mainly 5 lbs of boost and that was it. I also had black smoke coming from the exhaust. Sure sign of running rich.

04-03-2003, 11:00 PM
Does a leak have a direct effect (besides sparatic idle) like running rich? Im running a little rich and wonder if a small leak could cause that?

04-04-2003, 12:14 AM
It does if it is after the supercharger. The air gets compressed, which means that the air in the IC system to intake it at a higher pressure than out side the system. Just like a deflating balloon, air will travel from higher pressure to lower pressure. A leak after the supercharger means that air is leaving the IC system and not making it to the combustion chamber. The MAF registers an amount of air which tells the computer how much fuel to inject. If all that air is not making it to the chamber, but the fuel is, you will be running rich. And there isn't always a 'whistle' with one of these types of leaks either. Mine never did. Just never got over about 5 lbs of boost. But my collar nut was completely loose too.

04-04-2003, 12:36 PM
You might want to check the "breather hose" that connects the driver's side valve cover (looks like a PCV connection under the upper intercooler tube) to the rubber intake tube (bottom side, about halfway between the MAF and TB). I had a similar problem after getting some service done at a Ford dealership (that was a long time ago, I know better now.....) The "service tech" removes the breather line and didn't replace it. Caused all kinds of performance issues, and I could never get a boost reading above 5psi.

Just a thought