Hi, I have a 1989 aerostar extended van with 3.0 liter. It has a rough idle when I'm sitting at a stop light. It has never stalled yet and it has TONS of power when I want to get up and go. I have changed the wires, cap, rotor, plugs(have scars to prove it), fuel filter, and ran some fuel injector cleaner through it. It has been running for the past 40,000 miles like this and is not getting worse, is it time to maybe replace my fuel injectors? It has 184k on it right now and I would like to at least make it to 250k Also does anyone know what rear end gear ratio these vans have? 3.73 4.10 ?
As mentioned in a recent post, also replace the PCV valve. It's cheap so there's no reason not to. Another thing to consider would be the MAF/MAP sensor (not sure what was used in '89). Clean the throttle body and the idle air circuit and valve. Some people have found that a rough idle was caused by an idle speed that was too low. And, if you've checked everything and still can't figure it out, run a compression check. I chased a rough idle for a long time, and unwillingly went to two shops, only to find that I had a bad valve, which was revealed by a leakdown test.
Injectors could be the cause, but you shouldn't have to replace the fuel injectors unless they have failed. They can be cleaned with an ultrasonic cleaner for less than half the cost of replacing them, but you'll need to remove them. I found a shop that charged $17.50 each, but the more typical price is $25-$30 each.