Got a '94 ranger with Auto and 4.0.

Normal idle is somewhere in the neighborhood of 750 RPMs. Sometimes (50-70%?) when I'm stopped and have the transmission in OD and my foot on the brake the idle will drop to like 450 RPM and get real rough. It will "fight" the brakes some too and want to go but when I finally do take off it will stumble a little and then it's fine.

Other times it will idle normal. If the AC is on and I'm at a stop and the idle drops like that it will start running fine as soon as I turn off the AC. However it does act up even with the AC off sometimes too.

Any ideas?

Fluid level has been difficult for me to read accurately on the dip stick. When I got the truck (1 month ago) the ATF dipstick showed that it was low so I added ATF over the course of a few weeks in 1/4 quart intervals. The problem is that there's always a drip running down the dipstick from like 4-5" up the stick when I pull it out so I have to look for the sharp line across the stick which can be difficult to see. Overall I ended up adding a full quart to bring the bottom of the hashed area. Obviously I'm leaking somewhere but It's not leaking fast enough to really try to fix.

 

Sounds like it could be related to the IAC:
https://www.ford-trucks.com/forums/6...nsmission+idle

 

It does sound like it is linked to the IAC, has the battery reecently been disconnected? it may have been reseting the trim table. Or it could be a small vacuume leak causing the erratic idle. you say when the a/c is off you don't have the problem, thayt is because the load is increased and the IAC compesates for it. if you search around the forum there is a section that gives directions on how to "relearn" the trim table with the added load of the a/c

 

Yes, I have disconnected the battery. I was getting an occasional CEL for a rich reading from the left O2 sensor. The MAF was dirty so I cleaned it and reset the ECU to clear the code. So far the O2 CEL has not come back.

I can't remember if it was idling like this before I disconnected the battery or not. I'll look into the "trim table".

Thansk,
Jeff

 

LOL

i hate it when i can't remember what my truck ran like before i do something to it. Most of my buds call me a hypo because of my constant tinkering with my baby. I want her to purrr.i can't remember who it was, but the had an awsome link that described all the workings of ford fuel injection.. i found it very informative

 

Ok, I couldn't find anything about the "trim table" but I did see where people said not to just take off after reconnecting the battery or the computer will take longer to "learn" the idle.

I cleaned the IAC and put it back on and it sill did the same thing so I disconnected the battery for about 20 mins. After reconnecting it I started it up, turned on the AC, put it in OD, set the parking brake and let it idle like that for about 15 minutes. This seems to have fixed the problem after a short test drive but I'll have to drive it some more to be sure. Now it idles around 650-700 in park or neutral and 550-600 in drive with the brakes on whether the AC is running or not.

What is the idle supposed to be? It's lots smoother at 550 than it was at 450.

Thanks,
Jeff

 

672 RPM is the computers target, it does take time for it to really smooth out, after i reset the KAM i took a good 2 weeks for it to settle completely out. LOL that is if my memory serves me correctly