Hey all. 93 ranger 3.0 5 speed.
Until today the truck had no tach but I could tell by ear the truck was idling at LEAST 1k rpms. Also I could feel a random shake and quake at idle when sitting in the truck. I just bought the thing so I figured I would go through my normal tune up procedure and it would probably work itself out.
Charge battery with slow charge
flush radiator and block
new coolant
new thermostat/gasket
new temp sender (gauge)
new temp sensor (ECU)
new distributor cap
new spark plug set
new spark plugs (yes i did all 6)
seafoam in the gas tank

I also removed the air intake and used the MAF sensor cleaner on the MAF sensor. I hosed down the butterfly valve with throttle body cleaner and I unbolted the IACV off the top of the intake and let loose inside the holes with TB cleaner. I also shoved the nozzle down into the holes inside the intake and geysered the TB cleaner up out of there. A huge visual improvement.

So the truck definitely runs great but the idle didn't change and it still stumbles. No CEL, and CEL is functional. I hooked up my autometer tach tonight and sure enough it confirmed my suspicions: high idle. Gauge indicated somewhere between 1100-1200 rpm at cold and at warm idle. It revs smoothly and drives all around just fine but when sitting at stoplights the idle stays right here. Something else to note is when you FIRST turn the truck on it stumbles a bunch and idles low, like 500-600 rpm indicated. After 5-10 seconds it comes up to its normal 11-12 hundred.

So I'm no genious but my gut is telling me there is a small vacuum leak somewhere. I don't really know what to do at this point. What do you suggest I do? Or am I completely wrong? I have tomorrow to get this fixed so give me a list of things to check. A vacuum leak often gives these symptoms but maybe it could be something else

 

Get the engine up to temp, while engine is idling unplug the wires to the IAC, rpm's should drop engine may even stall, either is a good sign.

If rpm's stay high, you have a vacuum leak.

PCV valve could be stuck open or hose to it.

 

if it stalls what does that mean

 

Never mind. Got home and it was idling at 1200. Pulled the plug off the IACV and didn't miss a beat, still idling high. you say PCV valve, but I don't know what that looks like. Is that the fitting stuffed into the passenger side valve cover?

 

ok so i am not experienced with testing for vacuum leaks. Whatever leak this is must be pretty sizeable, seeing how my idle is at 1200. I did a quick visual test, couldn't see anything obvious or unplugged or cracked. Then I ran the engine and did two tests. The first was the brake cleaner test. I did a control by spraying it into the intake and the idle went up. I waited for it to steady and then went and sprayed everywhere I could see a connection.. Brake booster, pcv fittings, charcoal canister, that Tee off the back of the intake manifold, the joints in the intake tube, the IACV, all around the base of the intake manifold (that I could reach). The only thing that seemed to do anything was the brake booster fitting. It has some cracks in it but I couldn't replicate the issue so maybe it was something else. I took the hose off the booster and plugged it with my thumb, and this didn't change the idle. Still stumbles and idles at 1200. I then did the water mist test with my garden hose to try to see if I could see it being sucked in anywhere, or maybe stall the engine. Unfortunately the stupid radiator fan was blowing the mist everywhere so I couldn't see if it got sucked in anywhere but once again even spraying directly on the fittings did not make the idle change. You were saying the PCV valve can be internally failed? I'm completely lost on what I should do. Could a bad sensor also cause this?

 

Update: I went out and did a cold test of the IACV. I unhooked the IACV and took a picture inside. It is closed. I then turned it to KOEO and the IACV didn't move at all. Then I did an electrical test. about 12V to IACV plug with KOEO and the IACV pins ohmed to about 9.8 ohms no matter which direction my leads are placed. I read that when the engine is off the IACV is closed, but when you turn the key to ON it should open all the way to allow for easy starting. My test confirmed that my IACV isn't opening any during this test phase. Also with engine running it stays closed. I used a piece of cardboard and covered the holes but the engine was still running, so I assume I also have a vacuum leak AND a bad IACV? The iacv has a MFG 1992 sticker on it LOL. So get this, when the engine is turned off I can hear an air leak near the brake booster. It is ,my understanding that the brake booster is supposed to hold vacuum in the event of catastrophic engine failure so that the driver can still have power brakes for a short while. My brake pedal seemed to harden up (not 100% hard, but like 80% hard) on its own within about 10 seconds of the engine shutting off. Is this the brake booster elbow/hose assembly leaking? I need help here because this high idle is driving me nuts. I also did an ECU code check and only got 111 over and over which means no codes stored.




Posted here is the IACV ports when the engine was cold and not running. It looked exactly like this after I turned the key to RUN.

 

Anyone? I know theres some smart people here. I dont wanna be a parts changer.

 

I went outside again today to do some troubleshooting. I pulled the PCV out of the valve cover and checked that it rattles. I then plugged up the PCV vacuum hose and ran the engine, it still idles high. Then I pulled the brake booster hose and examined for damage. I plugged the booster hose and started engine. Still idles high. Then i pulled the hose off the tree on the intake that operates the cruise control box. Still no change. I busted out my propane torch and started gassing around all the gaskets and hoses trying to get an idle change but got nothing. Surely any vacuum leak big enough to push up 400 rpm would be affected by the propane gas. I ended up turning the anti-dieseling screw on the butterfly valve out one turn. I'm not sure if that was tampered with before but I adjusted it down to 800rpm hot idle. It seems happier. I don't have much history on the truck so I ordered a new IACV, new PCV valve (they are like a dollar), and a new brake booster check valve and grommet since I can still hear a hissing from it when I shut off the engine. My current theory is a previous owner had the IACV fail and they compensated by doing the old school trick and adjusting in the "idle screw" up some so it wouldn't stall. My other theory is when I go to start the engine later on a cold start that it won't be able to idle because of the bad IACV and the reduced idle screw adjustment. I'll report back later.

 

Truck wont idle cold. It barely hangs at 500 rpm unless i keep my foot on the gas. New IACV should be here this week.

 

Put new IACV on the truck, seems to have fixed everything up. I was right about the low cold idle, from my previous post. IACV fixed it.