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Need help desperately. I have no where else to turn.


CaveDweller94

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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 slightly rough. 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 the main problem is upon a heatsoak of 15-20 mins, when I start it, it’ll idle up down up down then die (approx 400-1500 rpm swing). Some times it won’t even idle up down, it’ll just start then die and then upon starting again, it’ll do the idle up down up down, have to give it throttle to make it stop. These are parts I’ve replaced.

IAC
TPS
MAF
PCM
Fuel filter
Fuel pump
Fuel pressure regulator
Battery
Checked/cleaned grounds
Air temp sensor
Coolant temp sensor
Coolant temp sender
All relays
PCV valve
Intake tube
Air filter
Plugs
Wires
Ignition coil
Ignition control module
Harmonic balancer
Crankshaft position sensor
Purge selonoid

I’m sure I’m forgetting something. I’m at a complete loss. I’m about to replace the thermostat because I did come across something while reading that it could possibly be stuck in open loop mode. It does run pretty cool. Which would make sense. But I have big doubts. If that solves my issues though I will praise the lord. But I am posting to see if anyone else has ever had this issue and if they ever found a fix. I’m at my wits end, please help!!
 


Rock Auto 5% Discount Code: F9A1A579ACFAD1: October 1st, 2021

RonD

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Hopefully the parts replaced were for other issues.

Fuel pump should shut off below 400rpms, safety feature, so engine will stall if idle ever drops that low, that would be normal.

Simple way to check if there is a vacuum leak is to warm up the engine
Let it idle and then unplug IAC Valve
Idle should drop to 500 or engine should stall, if it does either then no vacuum leaks

If idle doesn't change/drop then there is a vacuum leak

Cold engine idle should be 1,000-1,100rpm, and go down as temp goes up
Warm engine idle "target" is 700 with automatic trans, 750rpm "in gear"

If this doesn't happen then ECT, IAC or computer is out of spec

1994 computer is an EEC-IV, these had 3 Blue capacitors that could leak and cause odd issues
Have a look here: http://www.auto-diagnostics.info/ford_eec_iv

Pull out your computer and first check connector and pins for corrosion
Then open it up and look at circuit board, for corrosion or leaking capacitors, these can be replaced for about $5
 

CaveDweller94

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Thanks for the reply, I have tried all of that, I even replaced the computer... and unfortunately no it was not to solve any other issues than what was originally stated. Lots of time and money in this thing. All parts I described were new parts, no used parts. I have unplugged IAC and it does try to die. It idles at about 550 in drive. In park idle is perfect 700-750 warm. It’s as if the truck can’t decide whether the vehicle is warm or cold whenever it does the idle up and down thing. No codes are being thrown, although it does smell rich. I also have a jet programmer plugged up to it. But I removed it when I replaced computer and it drove great for a little bit til it learned then I was back in the same boat so I put the programmer back on it because it made a world of difference. Without it, the truck feels like a 4 banger. No power.
 

alwaysFlOoReD

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I've heard about problems with ground when using teflon tape on sensors. The sensors in question are one wire and use the body of the sensor to run ground thru the engine block.
 

RonD

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1994 has A4LD automatic, just above shift linkage on drivers side of trans is a Plunger type switch, the NSS(neutral safety switch).

NSS does a few things
Turns on Reverse Lights
Neutral switch passes 12volts to starter relay when in Park or Neutral
Sends voltage to pin 30 on Computer when "In gear"

The voltage at pin 30 causes computer to bump up idle(open IAC Valve) when you shift in to Reverse or Drive.
It reads like this is not happening
Idle at 750 should go up to 800rpm In Gear, generally about a 50rpm increase over all with the added engine load

I think it was a 5volt circuit, 0v in "neutral", 5v In Gear at pin 30

But can't remember if NSS acted as the Ground for the circuit, but it would make sense if it did
i.e. inside computer Pin 30 has 5v but no ground, so 0v, when NSS is grounded pin 30 is 5v now because circuit has a ground
 
Last edited:

Angie

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2 things strike me, plugged cat or o2 sensor needs replacing?
 

DannyG

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I would also look for frayed or damaged wires. Make sure engine/body grounds are good.
 

bobbywalter

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My credo
it is easier to fix and understand than "her"
Hopefully the parts replaced were for other issues.

Fuel pump should shut off below 400rpms, safety feature, so engine will stall if idle ever drops that low, that would be normal.

Simple way to check if there is a vacuum leak is to warm up the engine
Let it idle and then unplug IAC Valve
Idle should drop to 500 or engine should stall, if it does either then no vacuum leaks

If idle doesn't change/drop then there is a vacuum leak

Cold engine idle should be 1,000-1,100rpm, and go down as temp goes up
Warm engine idle "target" is 700 with automatic trans, 750rpm "in gear"

If this doesn't happen then ECT, IAC or computer is out of spec

1994 computer is an EEC-IV, these had 3 Blue capacitors that could leak and cause odd issues
Have a look here: http://www.auto-diagnostics.info/ford_eec_iv

Pull out your computer and first check connector and pins for corrosion
Then open it up and look at circuit board, for corrosion or leaking capacitors, these can be replaced for about $5

not knowing what pcm he has now its tough to say whats needed and what strategy and hardware setup he has now....

ass u me it is a 94 automatic. shit show year for consistent wiring.

these tend to need to see sig crank at 30...with no need to ground. technically you can run a straight crank wire to it. but not always. the manual is different...push in clutch or ngs grounds circuit back to common...





but....given the bury the Christmas tree under presents list of brand new shit that was installed..

looks like a case of unruly shitty spraying injectors to me...or wasted valvetrain...

or because of the injectors....both.
 


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