Very rough engine idle on cold or warm start on 90 Ford Aerostar; replaced fuel filter, no luck. Advice?

The IAC and the vacuum leaks are very good answers. But if it runs good when it warms up it probably is not a vacuum leak. An easy way to check for one is to get a can of carb and choke cleaner and spray around the vac lines. This will cause the engine to change speed. The map sensor is a good choice as well.

I'd start with some simple things first:

1. Check the fuel pressure. If it's weak then the fuel pump will need replaced.

2. Clean the throttle body. Lots of goop collects past the throttle plate and chokes off the fresh air supply.

3. Check the spark plug gap. If the gaps are too big from wear and tear they need to be replaced.

If these simple things are not the problem then it may need an engine diagnostic to identify the culprit.

Good Luck!

It sounds simillar to a fuel/air mixture prob', dirty fuel, or obstruction causing low fuel delivery via lines, pump etc. have ECM valve checked also. There can be several causes to this problem,(including air leak/ fule leak). Some of these are easily checked if you have a bit of time, if not it means a visit to a garage for a diagnostic check perhaps. good luck, hope you can find the prob' without the latter choice, (That could cost a bit depending on what they find).

One of two things. The IAC (idle air control) which is very common or a vacuum leak. If you hear hissing while at idle (get your head under the hood to pinpoint it) put your finger over the spot and see if it becomes stable. If you can find nothing, replace the IAC.

properly i might ought to assert that ' wager ' is your superb wager. It sat for a 365 days before you got it, and you have had it for a minimum of a one million/2 365 days. try doing a good song up. Like : plugs / wires / cap + rotor ( if equiped)/ air clear out , even an oil exchange, and upload some gas line a/f . sparkling your battery terminals and verify your coolant strenght. in case you probably did that , then maximum in all probability that van might initiate on the 1st try

It could be the air filter, spark plugs, spark plug wires, distributor cap, rotor, even fuel injectors needing cleaned. I would start with the running fuel injector cleaner through the gas and a new air filter. Start with the easiest and the cheapest projects first.