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If your idle is rough try completing the following steps and see if it corrects your problem:
1. First verify that your FPR (Fuel Pressure Regulator) is good. Pull off the vacuum tube and check for the smell of fuel. If no fuel odor is detected, then 99% chance that the unit is good.
2. Disconnect the aluminum preheater hose (if present) from your Air Filter box, unless you've recently verified that the Air Box Thermostat is good.
3. Remove the accordian tube that connects the Air Mass Meter to the throttle body. Inspect it carefully for wear and rub marks that might cause a vacuum leak (I just fixed this on my car last week). Flex it back and forth a bit and inspect it carefully for small cracks in the walls of the tubing. If you have breaks in the tube (typically due to rubbing on the strut tower), wrap the cuts very tightly with several layers of electrical tape or PVC-type duct tape. If neither are available, regular duct tape will work, but it has a lot of acids in the adhesive and will not help the longevity of the tube plastic. This is a temporary solution but it will work until you can get a new/used accordian tube.
4. Remove the IAC Valve (Idle Air Control Valve) and clean it with carburetor cleaner. While cleaning it, hold the unit so that the electrical connector points upwards (thus keeping the sludge from draining into the electrical motor body). Verify that the inner valve gate opens and closes easily when the unit is twisted rapidly in your hand. Re install it, being mindful of the flow direction.
5. Give the engine a quick check for vacuum leaks (2 tubes that run to the EEVAP canister under the driver's side headlight, 1 tube that runs to the interior climate control, 1 tube that goes to the Chrysler Ignition timing control unit, 1 tube to the FPR, and the various PCV/Flametrap tubes). If any of these tubes are cracked or have become hard/stiff at the ends, they would merit replacement. They should fit snuggly onto the nipples that they attach to and should not be loose or stiff.
6. Restart the car, and follow the Haynes or Bentley manual instructions for setting the idle speed. You will be grounding one test connector and adjusting a black thumb wheel on the throttle body. You will also need a tach, so if you haven't installed one in your instrument cluster yet, -here's a good excuse to buy one. (or borrow a hand-held unit from a friend)
After completing the above steps, you should have solved your rough idle problem. If not, here are a list of other possible culprits to investigate.
A. Spark Plugs
B. Distributor Cap
C. Spark Plug Wires.
D. Vacuum leak at intake manifold gasket (spray area with car cleaner and listen for a change in RPMs).
E. Bad temp sensor (there are two of them, one for the gauge and one for the computer).
F. Bad/failing AMM. (be sure to check for proper operation of the Air Box thermostat if you haven't already removed it or the preheater tube)
G. If you've gone this far, I'm running out of advise. The fuel filter should be changed if you haven't done so in the last 30,000 miles, but the likelyhood of this being the culprit is low.
God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 227K
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