I own a 2001 Focus ZX3 and it has developed a very unstable idle. (122,000 miles) While AC is on, the engine seems to rise in RPM and smooths out as normally as it always has. When AC is turned off, the engine has started torise and fall in RPM almost downto the point it seems as if it is going to stall. It runs smooth while travelling but when stopped, begins the aforementioned roughness. I replaced sparkplugs and still the same. It doesn't seem to have any problem going down the road. Power seems fine. But when stopped, idle is terrible. I thought I had got bad gas but I ran the tank way down and went to a place that I always got gas from and it still has the problem. Any techs our there have any suggestions? I reada post about the potential AC clutch problem, but this seems different. It sounds as though AC disengages/engages perfectly. No strange noises etc etc.It seems as though it's only in the idle.

P.S. I searched my VIN on the Ford site and it doesn't state a recall for a fuel pump or anything. Wouldn't a fuel pump affect the car at any RPM though? Mine's fine other than at idle....I do remember having to take it back for a Sensor replacement, but when that happened the car had a loss of power while going down the interstate even along with a rough idle. Anyhow, any help would be greatlyappreciated.

 

Update to my post

I changed sparkplugs and the car still has the problem. I started it when I installed the plugs and it ran about a minute and a half and died.Now it seems as though the car isn't getting any gas at all. Turns over but wont start. I checked and its getting good fire. I'm thinking fuel pump, any other suggestions to try to diagnose? No check engine lights, or anything has came on since I have had the problem appear. I guess the ultimate question would have to be if the fuel pump going bad would have made the idle irregular on it's downward plunge. Next question would be, anyone know of a forum that shows the process of replacing the fuel pump? My only form of transportation so i'm quite desperate and in a hurry to get it repaired.

 

Fuel filters are the number one cause of fuel pump failures. There is no bypass for a fuel filter, when it clogs, it makes the pump work hard and burns it out. You can try replacing the fuel filter but the best thing to do is get a reading of your fuel pressure at the rail. You can buy your own fuel pressure guage or a shop already has one. In either case, you will spend a few hundred dollars to fix it if it's the fuel pump. Let us know what the fix is.

 

yeah I realize this was postedover a month ago but i understand what your saying cause my ZX3 is at 75000 miles and its almost doing the same thing but it catches itself and doesent stall but from what I see you wrote its probably just a matter of time for me to have your problem...so let me know wht you find out....im also going to run my vin to see whats not been replaced i dont think the last owner did too well on keeping up with the recalls...which could be another question do you know of any recalls that are dangerous if not fixed???... your feedback will be very helpfull!!!!!