Here’s another idle problem. I have a 1992 aerostar, 3.0 2wd with 245,000 kms.

I have been working on this van for weeks now getting it ready for summer. I have done a complete tune up consisting of wires, plugs, rotor, cap, pcv and all filters including gas, air and oil. I have checked the vacuum hoses as best as I could and all seem fine.

Here’s the problem. I start the van and it idles great. The engine doesn’t move. After a few minutes it slows down a bit and starts to shake. Once it is completely warm and has been driven for an hour, it shakes noticeably. It has lots of power and gets good mileage. It never has a starting problem and never seems to be close to stalling. I am suspecting it is one of the various pollution control items such as the MAF, IAC or 02 sensor. Is there a way to check them at home?

While under the van, I noticed a cable that goes from the transmission into the firewall. A bracket holding it in place broke and the cable was rubbing against the exhaust pipe and burned through. Could this be related? I taped up the cable and tied it up and away from the pipe.

Any ideas of what to look for would be appreciated. Thanks.

 

Is the idle RPM at spec. when the condition occurs?
You indicate that you replaced the plugs... What was the colour/condition of the old ones?

 

The idle rpm seems a little low and goes up and down between 500 and 600. the plugs looked perfect. all 6 were a light tan color and looked good and dry. I change them every 40,000 kms.

 

Well the plug condition tells you a lot, you at least know that it's not running lean or rich which is good.
If you bring the idle up very slightly does the shake diminish at all?
Dont know whether or not you have the space, but what I did was buy a parts van for a hundred bucks, this way I have all the spare parts to swap over for testing.

 

Have you ever replaced your Idle Air Controld Bipass Valve (called IAB or IAC)?

If not with that kind of millage I would try cleaning or replacing it. They tend to get gummed up over time. Common problem on all Ford models.

 

To answer aerocook, even if I just lightly touch the gas, the engine evens out nicely, no room for a spare one, I used to have a spare car for parts, but would be divorced if I still had it.

For 93nighthawk, I have never replaced the IAC or the 02 sensor. I don’t know what the problem is so I didn’t want to just start replacing things as they are expensive parts. It seems that the IAC may be the likely item

 

If your not in the mood to buy a new IAC you can try cleaning the IAC but it will take time you really need to clean it well.

In most cases if you clean it you should be good as new but there are rare circumstances where that isn't enough and it has to be replaced.

 

You should replace the o2 sensor once ever 100,000 miles. Many people would argue about this, but if you look at the maintenance schedule recommended by Ford, they recommend replaceing it a lot more often than that. I distribute converters for a living, and most converters that need replacement failed because the vehicle was not proberly maintained, and the number one cause of converter failure is the O2 sensor.

 

It’s interesting that you talk about when to replace the 02 sensor or what to do to the IAC. I bought the van used and never got an owner’s manual with it. I bought a Haynes manual for it and have used it till the pages started to fall out. I even have the 1992 service manual from Ford for the engine. Nowhere does it talk about replacing the 02 sensor at any interval, it just tells you how to replace it. As for the IAC or IAB, other than on this forum, I can’t find any reference to it anywhere.

I guess I’ll start by cleaning the IAC, but I need to know where it is and what it looks like. Is it called something else? Can someone tell me where it is on the 3.0? Perhaps a diagram or picture. The closest item mentioned in the Haynes manual is an Extended idle air bypass system, but it says this is on the 2.8 engine and the only thing mentioned for the 3.0 is an ABV or air bypass valve. Is this it? Thanks

 

IBV is it (I think) It is a round cylinder connected to the intake on the opisite side of the throttle body. It is a pain to get to and out (being held on with torx bolts, whats wrong with normal hex nuts. ) Use some Berrymans B-12 and really spray the heck out of it.

 

O2 sensors work chemically, and the chemical does get depleted after a while. People don't realize this so they keep on thinking that something that doesn't move cannot be broken, hence doesn't need to be replaced. It clogs up your catalytic converter after a while. I replace mine every 60,000 miles whether or not I got a code. For the Aerostar, it's cheap and there is only one of them, not 4 like some other newer model cars.

 

Looks like I will change out the O2 for sure, as for the IAC or IBV or what ever it is called, is it a difficult part to remove? Is there a chance that the bolts can snap or will they come out fairly easily? I had a look, and it doesn't look too hard if I remove the black plastic that is covering the part. The plastic is held in with plastic clips that have to be broken to get loose, so I guess I will replace them with nuts and bolts.

 

Just try to loosen them first and if they don't budge don't try to force them or you'll probably break the heads spray some pentrating oil on them and let it sit then try again be sure to put some anti-sieze on the bolts before you reinstall them .

I put that stuff on every bolt I remove on the engine.

 

I'll give this a go on the weekend. If anything breaks at least I'll have plenty of time to get it out. I can't believe how expensive these little parts are. 85$ canadian for an O2 sensor.

 

It could possibly be the MAF sensor. I replaced mine with one from Autozone and it lasted about a year and a half so i put on my old one after cleaning it and all code were repair and the truck is running like new again.