phantom acceleration

[rayinala]

I recently bought a 93 Ranger 3.0 automatic, It was/is running, but rough. It was especially hard to start when cold. The PO had replaced a water pump (new), fuel pump (not sure if new), TPS (junkyard), MAF (junkyard), IAC (junkyard) and there were a few spare fuel injectors in a can in the truck. Obviously, he had done things with the fuel injectors. I bought a code reader and have seen many different codes as I replace parts and recheck codes. I've bought new (but not OEM) MAF, Temp sensor, EGR, DPFE, TPS, IAC, air cleaner (there was none!). I've really gotten places with these replacements, but things are not quite right. When I am driving it sometimes feels like cruise control is on (truck does NOT have cruise) and the truck will drive along at 45-50 without touching the gas. When I come to a stop, it will act like you all of a sudden removed your foot from the gas pedal and it stops fine. I've been cruising along at 45 with my foot Off the pedal, moved the truck into neutral and could hear that the motor was revving. after a moment, I can hear the "foot come off the pedal" and the idle backs down. When I put it back into drive and accelerate, after a moment or two, it holds the acceleration - like cruise control. I stopped on the side of the road, the truck idled down and I disconnected my IAC and it made no difference. BUT, with it disconnected the throttle sticking stopped.
I believe I have an air leak and thats why disconnecting the IAC has no effect on the idling truck? I've sprayed carb cleaner looking for a vacuum leak, but do not get any surges.
I know the rubber seal at the large plastic air intake hose is missing, but I don't think that would be an issue (the intake between the MAF and the throttle body)
Maybe a vacuum leak under the intake plenum? Maybe o-rings at the injectors?

 

[franklin2]

I have never worked on a 3.0, but on the older engines, another sign you have a vacuum leak is to back the idle stop screw back. If the engine still idles with the throttle butterfly completely shut, that is a sign it is getting air from somewhere else to run. If it does stall out when the idle stop screw is turned back, then it may be simply someone turned the idle screw in too far.

When you unplug the IAC, the engine should barely idle, turning very slow. But like I said this is for the older 2.9.

 

[rusty ol ranger]

Do not mess with the idle stop screw. Its calibrated and getting it back where it needs to be is a about as fun as a root canal.

Also lubing the throttle body spring/shaft on the outside to see if itself is sticking. My 460 would do this once in a while when i first got it, soaked it in white grease, worked it back and fourth, and its been fine since.

Injector O rings shouldnt cause this issue. However a intake plenium leak very well could.

Also the fact youre getting numerous codes points that you may have a wireing issue or even bad ECM.

 

[rayinala]

Thanks for the responses!
I've not ran the OBD1 and checked for codes since I replaced the last parts. But, the CEL is not coming on which is a good sign to me.
I've not checked nor messed with the idle screw and don't feel that is the issue.
I'm going to try and describe the issue again.
Before replacing many parts, the truck was hard to start when cold. Had to flutter the gas pedal to keep it running; once warm it did ok but poor idle (loping, almost stalling)
Replaced parts and then had much better cold starts and good warm starts...But, driving down the road it would feel like the throttle was on even when I removed my foot from the pedal.
To me this felt like something is "pulling" the accelerator on. When I come to a stop, the motor is high RPM at first but within 30 seconds it would idle down properly.
So, driving down the road I shifted into neutral (cause I could feel the truck gaining speed with my foot OFF the pedal). When I shifted to neutral, I could hear the motor revving, but within 5-10 seconds the revving would stop.
I put it back in gear didn't touch the gas pedal and the idle stayed down. Accelerate and once again it would feel like the throttle sticked. I feel it acted like some type of vacuum issue "pulling" the accelerator on.
I stopped on the side of the road, disconnected my IAC and the phantom acceleration stopped. Completely. Idled ok at stops and all and did not feel like cruise was on.
When at a stop, plugging unplugging IAC has no effect. Unplugged IAC gives me the same hard start issues. But it stops the phantom acceleration.
I feel like I have a bad air leak somewhere. Tried spraying Carb cleaner and it makes no change. Air leak must be somewhere carb cleaner is not getting to

 

[19Walt93]

It doesn't sound like your throttle is sticking, I think the IAC is sticking and needs to be thoroughly cleaned. Probably because the knobhead was running with no air filter. Remove the IAC, separate the solenoid from the valve and clean the valve with throttle body cleaner, not carb clean. Then clean the throttle body and butterfly with the same stuff. After working for decades at a dealer 1/2 mile from an Autozone, I'm very leery of aftermarket electronic components because I've seen too much time wasted chasing the problems they caused. I'm also leery of aftermarket scan tools set up to display their guess of a diagnosis- Autozone would get a rich or lean code, the scanner would say "O2 out of range" or something similar, and they'd sell an O2 sensor. O2 sensor out of range is a symptom, not a diagnosis. The DTC's are intended to send a tech to the start of a diag path, not to the parts counter.
Unless new parts are unavailable, I'd never buy used electronic parts or sensors- I'd compare it to buying a used tooth brush or condom.
By the way, Ford calls the check engine light a MIL-malfunction indicator lamp. I don't know where CEL came from, maybe the same guy who calls every limited slip a "posi". A posi is the rear end my Chevy friends kept breaking before they swapped in the 9 inch Ford or Dana 60.

 

[rayinala]

If the vehicle is warmed up and idling fine, shouldn't the motor stumble or stall when I unplug the IAC?
I will be replacing the new Duralast IAC (autozone) with a Motorcraft one soon.
When the motor is warm and the idle is "calmed down" (drive, come to a stop, high idle for 10-30 seconds, then it "comes off" the high idle)
Well, when I then unplug the IAC it has no effect.
Vacuum leak?
By the way, your v8 swap sounds nice. I have a 62 Ranchero that I swapped in a 5.0 and a C6. Still a project, but I'll get there someday. 8.8 rearend, mustang II front end and even more unique (than the electric steering) In-dash A/C

 

[rusty ol ranger]

If the vehicle is warmed up and idling fine, shouldn't the motor stumble or stall when I unplug the IAC?
I will be replacing the new Duralast IAC (autozone) with a Motorcraft one soon.
When the motor is warm and the idle is "calmed down" (drive, come to a stop, high idle for 10-30 seconds, then it "comes off" the high idle)
Well, when I then unplug the IAC it has no effect.
Vacuum leak?
By the way, your v8 swap sounds nice. I have a 62 Ranchero that I swapped in a 5.0 and a C6. Still a project, but I'll get there someday. 8.8 rearend, mustang II front end and even more unique (than the electric steering) In-dash A/C

Yes unplugging the IAC should at minimum cause a drop in idle. Maybe you got a bad one off the shelf

 

[rayinala]

after reading/researching a lot, I do believe the IAC needs to be replaced (again) with an OEM item.
But still, shouldn't an unplugged IAC cause the motor to stall or stumble?
The last time i used the Equus Ford OBD1 reader, it was all clear (111) with the KOEO. When I tried the KOER it threw 2 codes (don't recall the numbers - but it was "unable to control idle high" and "unable to control idle low"
I have 2 IACs that came with the truck. One was on the motor and obviously came from a junkyard. The other was on the floor and I think it is probably the original one.
I will clean up the original one, install it, and let yall know how it goes.
Thank you Very Much!

 

[cbxer55]

IAC's for these are notorious for being finicky. Mine would eat the el cheapo made in Mejico IAC's that Vato Zone sells. Last time, I saw they sell a premium made in Japan Hitachi part. Bought that in 2015, haven't had another IAC issue since. Also put one on my 2004 Lightning the same year.

Prior to that, mine was having the same issue with suddenly wanting to take off while idling at a stop. Or suddenly, just dying out while cruising on the highway at 70.

 

[rayinala]

So, I removed the brand new Duralast IAC, installed the old Ford branded IAC and all of my problems went away!!!

Lesson I learned today (with the GREAT HELP of forum members) is, when replacing electronics or sensors, spend the extra money and get the parts the dealer would use. OEM parts.
Thanks again to all who helped!