94 ranger rough/low idle

[CaveDweller]

This will be a long post, but I’m reaching out becuase I have no where else to turn. I’ve read pretty much every thread on the internet pertaining to the problem I’m having and nothing has worked. So here’s the problem... idles ever so slightly rough, almost like a small surge. When I put it into drive it’ll drop idle to like 300-400 and voltage will drop and then it will catch itself and go to 500. Same story for reverse. In park it idles at probably 650. Also when driving, between rpm range of 2000-3000 it will almost hesitate and then begin to climb rpms again, like it’s fighting itself and it’s very consistent at doing this with or without the AC on. Speed still is climbing when this happens. WOT runs pretty great. I’ve checked every vacuum line at least 10 times. Spray carb cleaner around everything, no change. I have not pulled vacuum yet but plan to do that next week. Here are the parts I’ve replaced trying to figure out this problem... also originally the main problem was upon a heatsoak of 15-20 mins, when I’d start it, it’d go up down up down then die. That problem has since been solved by replacing the following.

IAC
TPS
MAF
PCM
Fuel filter
Fuel pump
Fuel pressure regulator
Battery
Checked/cleaned grounds
Air temp sensor
Coolant temp sensor
All relays
PCV valve
Intake tube
Air filter
Plugs
Wires
Ignition coil

I’m sure I’m forgetting something. Suspects are crank shaft position sensor since it’s sort of an intermittent problem, torque converter, just simply needing to adjust idle up some, coolant temp sending unit, carbon canister, blocked vacuum line, something internal with the motor... I have not done injectors becuase I am lead to believe they would not cause this issue. I even unplugged one just to see how the motor would run if it was missing and it was totally different. Also unplugged MAF and it almost died then idled like crap til I plugged it back in. Also I could just be going crazy and this is just how a 24 year old ford 4.0 is supposed to drive. But I don’t think so. My next step is checking vacuum with a gauge and then checking compression. Or adjusting idle by using the method of unplugging iac and adjusting idle until it runs with it unplugged. Also there is no play in the throttle cable. Maybe a 16th of an inch but nothing to be concerned about. If there is any info anyone could give me, or just simply some other ideas, or even calling me crazy from trying to solve a non existent problem, please tell me. I’m all ears for anything. I’m all out of ideas and money. Thanks in advance!

 

[Rick]

Intake manifold gaskets are known to cause vacuum leaks on the 4.0. That's one thing you haven't mentioned.

 

[CaveDweller]

Intake manifold gaskets are known to cause vacuum leaks on the 4.0. That's one thing you haven't mentioned.

Wouldn’t the carb cleaner trick, spraying around it revealed that it was leaky?

 

[massacre]

I was getting signs of a vacuum leak, went nuts trying to find it. Ended up being dirty MAF

 

[CaveDweller]

I was getting signs of a vacuum leak, went nuts trying to find it. Ended up being dirty MAF

Yea I wish it was just that simple. Since I replaced MAF with a reman I don’t think it’s that. I’m really pointing towards a weird transmission problem. I need to also check the vacuum lines to it. I did actually discover a broken vacuum line for my AC that went to the vacuum reservoir. All it did by fixing it was make my AC blow significantly harder. It’ll take another day or two of driving to see if it helped anything else. Transmission vacuum lines are the next thing to check though. Those are the only lines I haven’t checked.

 

[RustyMacintosh]

I know its un-American, but I bought a new MAF off Ebay which came from Bulgaria for my 94 XLS. 6 months later still working as it should. Cost me $37. shipped.

Mass Air Flow Meter (MAF) Fits Ford Lincoln Mazda Mercury 718207777464 | eBay

 

[massacre]

Yea I wish it was just that simple. Since I replaced MAF with a reman I don’t think it’s that. I’m really pointing towards a weird transmission problem. I need to also check the vacuum lines to it. I did actually discover a broken vacuum line for my AC that went to the vacuum reservoir. All it did by fixing it was make my AC blow significantly harder. It’ll take another day or two of driving to see if it helped anything else. Transmission vacuum lines are the next thing to check though. Those are the only lines I haven’t checked.

It blew harder prob because the vacuum door opened more. Hope you find the issue I know it’s frustrating as hell

 

[CaveDweller]

It blew harder prob because the vacuum door opened more. Hope you find the issue I know it’s frustrating as hell

Yea I know it. I’ve put over 1000 in it and it’s still just being weird. I’m to the point to where as long as it ain’t shutting off or trying to, I’m just going to let it ride til something major happens. The sketchiest thing at this point is it just acting like it wants to die for a second when I put it in drive or reverse. And it’s like it’s only 150-200 rpms off. That’s all. That’s also why it’s so frustrating, is it’s such a small problem but a problem nonetheless