My wifes 89 Aerostar with a 3.0L, has come up with a new twist.
We just had the A/C converted from R-12 to R-134 and everything was working fine, however, after a week or so it started stalling at intersections, and the mileage went down the drain...6-8 MPG. We took it in to a shop, and they replaced the O-2 sensor. No change. They said it was the MAP sensor, even though there was no code for the Map sensor. Changed the Map sensor, no difference. Thankfully Autozone took the part back. Ran the code checker, and it gives me code 89...I took the van into the dealership, they seem to think that the computer is dead, but this makes no sense to me. If we run the van without A/C, it seems to work fine. Turn the A/C on, and it acts up again.
The Engine was replcaed 2 years ago, 10,000 miles on it. And the Transmission (auto) was just replace, 1,000 miles on it.
Any suggestions would be most appreciated...

 

Welcome to FTE!

Sudden poor mileage and stalling usually points toward the fuel pressure regulator going bad. The tie in to the A/C usage is a bit of a puzzler unless the common thread is the conversion work done on the A/C system. If the work involved pulling and replacing all the o-rings in the A/C system or major parts exchanges, there is a good chance the vacuum line to the fuel pressure regulator and the electrical connection to the idle air control valve has been disturbed.

The fuel pressure regulator (FPR) is found on the fuel rails that feed the injectors. It is a compact, round, metal affair, with two fuel lines plumbed into it and a vacuum line. If the line is off or split at the connection point, replace it. If the line appears intact at the connection to the FPR, remove the line and see if it is wet with fuel inside the vacuum line. If so, the FPR is definitely bad and needs replaced - and promptly. Excess fuel into the catalytic converter will overheat and ruin the catalytic honeycomb.

The idle air control valve (IAC) is found on the side of the throttle body. It is an electromagnet and small pin that serves to step up the idle speed under engine load, i.e. when the A/C is turned on. Often the pin gets gummed up and sticks open/closed and causes problems. You can easily remove it and spray it with carb cleaner. Often this will solve the problem. If really gummy or worn, it will need replacement. If this is still the original unit and not replaced during the engine swap, then you have sufficient mileage for it to be a prime suspect.

Hope this solves your problem(s).

 

Thank you for the info...I will let you know if this helps!!!

 

Since it seems to be related to the A/C, check to make sure that the compressor is cycling on and off like it should be. It could be stuck on full time. Also, maybe there's something wrong with the compressor and it's causing excessive drag on the engine. Does it feel like there's a large load on the engine when the A/C is on?

 

I looked at the FPR and it seems to be ok, double checked all the connections.
The IAC valve was a little dirty, so I cleaned it as well.
The wife reports that the vans is running fine now!!
Thanks again aerocolorado! I am not sure if there was a loose connection with the FPR or if I just have the touch....

 

As long as the wife is happy --- you have the touch. Glad to hear all is well again.

 

Ok, I've been looking for my IAC valve, but my haynes manual doesn't show a good picture of it. Which side of the TB is it on when you look at the engine from the front? I have a feeling this is causing some of my problems.

 

I just cleaned my IAC valve about an hour ago. It is located on the top of the Throttle body. If you follow the air intake duct from the air filter then is passes the Mass Airflow Sensor then the duct follows along just above the the radiator then turns in toward the engine. The tube ends at the Throttle body. There is a shroud attached on the right side of the throttle body (as you are looking into the engine compartment). Once the shroud is removed you can see it on top and to the right side of the throttle body. The connector for the IAC valve is almost right above the air intake for the throttle body. My IAC Valve is about 3 - 4 inches long and about an inch and a half wide, silver and kid of tube shapped with a black connector. It is held onto the the Throttle body by 2 small bolts. They are either 8mm or a 5/16. My were kind of rusty so i used the 8mm because it is .06mm bigger then the 5/16 and it seemed to fit better.

I also cleaned my Air Flow sensor while I was in there. She Idles a lot better now!

Hope that helps
Doug

 

Thanks a ton for the info (don't ask how mad I was that the manual didn't point out where it was)!

I'll pull it off tonight and clean it, hoping that will take care of my lopey idle and stalling problems.