'91 Town Car, Won't Idle!!

You can go about this problem a couple of ways. You can start with the routine maintenance items like cleaning the throttle body, ISC and MAF sensor. Make sure the engine is in a decent state of tune with respect to plugs, air filters, etc. That failing, the next item I would try is replacing the ISC which is what the computer uses to control the idle speed. They can test good electrically but, still be sticky preventing them from working properly. Cleaning as above many times will cure this problem. If the problem is still not corrected, you should have a properly equipped shop do a diagnostic scan of the system to determine any fault codes and how the various sensors are performing. Without this info, you can throw hundreds of dollars worth of sensors and controls at it without correcting the problem.

lugnut:

Where's the ISC and MAF located? On the intake manifold?

I'm going to try cleaning both of them.

Thanks.

hi robin - that's about the right mileage for the problem to pop up. go to the passenger's side, and to the pvc valve that is sticking out of your valve cover. follow the hard plastic tubing to a rubber type "T" fitting at the back of the engine at the level of the lower intake manifold. you will probably find a hole in the middle of the "T" where it has collapsed and is allowing air to come in and upset the air fuel mixture and it will idle very rough, but perform normal in other ways. costs is less than 10 dollars at lincoln and they have the part on hand. it's a common consumable item on the 4.6 engines.

hope this helps,

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional "Many more men die with prostate cancer than of it. Growing old is invariably fatal. Prostate cancer is only sometimes so."

The ISC is located beneath the left side of the throttle body. Removing the throttle makes it easier to get at but, it can be gotten off with a lot of patience and a long 1/4" drive extension and socket if you have long enough fingers to reach in and start the bolts to reinstall it. The MAF sensor is located in the air intake tube near the air cleaner box. It has a wire harness connected. It is very fragile. A cotton swab and some residue free electronics cleaner works well for cleaning. Sometimes, a couple of shots of throttle body cleaner works well. You will need a torx bit of the correct size for a tamper resistant torx head screw to remove it. Most parts houses have a small set that is inexpensive. Again, any of this work requires a great deal of patience and care to avoid costing yourself even bigger bucks.

Start with the ISC (idle speed control motor) Its on the throttle body. It bolts on and has an elect. plug on it. Remove it and clean it. Check inside the throttle body for dirt/grime too. Remove the rubber intake hose from the air filter where it goes the the metal throttle body, if its dirty clean it and the throttle plate. Like lugnut said, its probably the ISC . You have no check engine light comming on right? GL