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Q: Rough Idle on 2000 Mercury Villager

Read forums, tried disconnecting MAFS, O2 and TPI sensors. No Luck. I ran concentrated injector cleaner through gas... Worked for 2 weeks! Problem returned.. Tried same treatment... no luck this time! Thing runs like a champ when driving / accelerating. AutoZone's reader couldn't establish communications with my ECM. Tried two different Autozones... same problem.. Rotor, cap and plugs were replaced 12,000 miles ago.. The intermittent symptoms are driving me crazy! Once, I tapped on the Mass airflow sensor... Fixed it for about 4 days... What am I missing??
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I know this is an old post, but hopefully it might help others that have had similar issues since. I had similar symptoms, thinking it was the fuel pump, water in the fuel, etc. Replace the fuel filter, cap, rotor, etc, Van was still bucking and had a rough idle, stalled, almost zero acceleration. Try cleaning in the crankshaft position sensor, located in the distributor, under a metal plate beneath the rotor. Spraying with a sensor safe cleaner. If it still persists, you need to replace the distributor. (For me, it was the distributor) Been running like a dream since. Hope this helps.
What is Villager doing wrong? You mentioned a lot of parts and problems with the data link but lets a start with your primary complaint. Oh, the code reader may not work because your cig lighter fuse may be burned out and this powers up many data link connectors. ( believe it or not) Let me know Happy 4th ( hopefully)

the cig lighter issue is the FUSE for the cig lighter that also powers up the Data link socket which allows you to read the codes with a code reader. Check the fuses, it may be called the courtesy fuse, cig fuse etc on the inside fuse panel. ( this fuse blows often when people recharge their cell phones or use the lighter or an I-pod)

As far as your Villager goes, it could be a sticking open EGR valve or a Vacuum leak, if, as you say, it runs fine at road speeds. Repair the code issue, because your Villager has OBD-II which is a very helpful Diagnostic system.
Thanks. It runs very rough at stops. (idling)... Like a few plugs are out ..... Plugs were replaced about 12K miles ago... Runs great when driving / accelerating.. Thanks for the info about the cig lighter... not sure about it but will check...
My 1999 Villager was running poorly; rough idle, lack of power at highway speeds and the engine problem light indicated random miss-fire, etc. I had new spark plugs so I felt these were not the problem. I cleaned the mass airflow sensor: no improvement. A New air cleaner helped but did not solve the problem. I cleaned the camshaft position indicator plate and sensor (inside the distributor): no improvement. A new distributor finally got the engine running well at highway speeds and the check engine light stays off now. However: the engine still idled poorly. I've also had, for a long time, a "sticky" throttle, where the throttle does not want to open from idle, especially first thing in the morning. Both this and the rough idle were fixed with one simple adjustment of the idle stop on the throttle. Over the years things had worn and the throttle was closing up too far, causing it to stick and also causing the rough idle. By opening up the throttle adjustment a bit, both problems went away. With the throttle closed too far air leaking around the shaft was acting as a vacuum leak, causing a rough idle.

By the way: in replacing the distributor, I did it without going through the process of rotating the engine to top dead center, piston #1, compression stroke. I simply carefully noted the position of the rotor after removing the cap. I used a piece of making tape placed in a convenient location so I could aim the rotor at a pencil mark placed on the tape. Upon removing the old distributor body the rotor will turn a bit. When installing the new body simply start the insertion from this position, then check the final rotor position by the mark made earlier. The whole process took about 10-15 minutes. It was easy to place the new distributor in the same timing position as the old and checking with a timing light showed it to be timed correctly at that spot.
I have had this problem with the mass air flow sensor. If your mass airflow sensor you will get codes indicating such. I was actually able to take the old one apart and resolder some bad solder connections in the module and it worked fine after that. I don't recomend taking it apart yourself unless you know what you are doing. The small wires that go to the outside connector are welded to pads and come loose, unfortunately these wires are aluminum and cannot be soldered with rosin core solder, they must be replaced with copper wire. The wires are very tiny and delicate, I use a strand of 20 gauge stranded wire as a new wire. I start by cutting the very top of the plastic cap of the sensor assembly off with a dremel tool. A fine tipped soldering Iron is required. Good luck if you attempt this.

If the Mass Airflow Sensor is dirty it will have an effect on the Idle but usually not set the check engine light.

I have also had poor idle issues because of the Idle Air Control Motor died, it did not set the check engine light. The Idle Air Control Motor controls the idle speed of the engine under different loads. There is a base rpm it is set to, while unplugged, and then it controls the idle above that by changing the amount of air bypassing the throttle plate.

Another poor Idle issue I have had with this vehicle is the Knock Sensor. The knock Sensor self destructs in time and becomes extremely sensitive, it will set the check engine light and a code. I initially installed a cheap china knock off and it barely out performed the broken sensor. As a result I had to replace it with a top brand part. Tip: the knock sensor is under the intake manifold and is very time consuming to replace, many people splice into the old sensor wires and mount the new sensor on the other end of the block in a convenient location and get good results. Note: the knock sensor wires are a coax except at the connector where it is split into two separate wires to go through the connector.

I have also replaced the distributor to resolve poor idle issues, the bearings in the distributor are notorious at leaving material on the sensor ring and having excessive play causing a poor idle.

P.S. If there are no codes start with the cheap stuff first, plugs, wires, cap, rotor etc.
Good Luck
just in front of the firewall closest to the driver, there is a plastic container with a vacuum line hooked to it, in my case, this vacuum line needed to be pushed in. Also, for some reason, the throttle cable thingy that is a pinion that rides on an arc was up on the lip of the arc. [I bent it outwards so that wouldn't happen again.] That made for a high idle that the automatic control couldn't compensate for... It didn't help that my battery cable was loose. My gas was questionable and probably is what popped the vacuum line off, spark plug wires were cheap and never had confidence in them either. My beloved Mercury Villager/Nissan Quest lives!!!
Had a mechanic figure it out.. A bearing in the distributor was bad. This would cause the distributor (rotor) to bind up for a split second numerous times throughout the cycle. I replaced the distributor and it runs great! Gotta love those Nissan engines! UGH!
HA! The iron bolt that clamps on my distributor, would synch in, but I took it out anyway and it had dethreaded the aluminum hole. Thats why after setting the timing everything would go kapewy over time. I bored it out for my new aluminum bolt, put on the easy out goo and it cut a new thread just fine.

Thing runs so tight on the highway BUT cold damp mornings are not my friend, time to look at the IAC valve and air temperature sensor...
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