2.3L ('83-'97) Need help figuring out an idle issue

[ss27gogeta]

Truck is a 94 ranger 5 speed 2.3l. Here is the problem when I'm coming to a stop the idle will bounce around for a few seconds. then the rpm will hang high for a few seconds then it will settle down to a normal idle. Truck has New Iac pcv coil packs plugs and wires cleand out throttle body none has helped the issue. Over all truck runs grate starts easy accelerates as it should. dose not give me any issues at speed on the road either. It dose have a check engine light I've tried to pull codes watched a few videos to makes sure I was doing it right. and for some reason it won't flash the codes when I tried to jumper the wires. could it be the maf sensor or maybe o2s truck has 107000 miles on it and I believe both are original to the truck. Thanks.

 

[ss27gogeta]

Ok got the codes to work I got 112 122 157 172 and 332. Looks like I might need o2s and an egr and it looks like I have a bad ground somewhere according to these codes.

 

[RonD]

Upstream O2 needs to be changed every 100k miles or 12 years which even comes first, its the only sensor that actually wears out
My 1994 has all original sensors except for O2s, and original IAC and fuel pump, knock on wood


112 Intake Air Temperature (IAT) sensor is/was low or grounded - IAT
122 TP low (possibly grounded or open circuit) - TPS
157 Mass Air Flow signal is/was low or grounded - MAF

172 Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control
332 EGR did not open/respond during test or if memory code, did not open intermittently - EVR or PFE

I would pull out the computer and check the circuit board, specifically the 3 blue Capacitors, just replace them on spec in any case, because it WILL need to be done even if they are not bad now
Under $5 fix

The computer uses a 5volt reference ground, grey/red wire seen on IAT, TPS and ECT sensors, also sensor wire on O2s and tan/blue on MAF sensor
Also on EGR sensor

That's what all the codes have in common
TPS is easiest sensor to get at, test its 3 wires for voltage and ground
Brown/white should be the 5v but grey/red can also read as 5v because these circuits are "pull down", its an electrical circuit type that allows for varying voltage, like in a vehicle, but can still "read" sensor voltage difference(data)

So my guess is its a computer or computer connection issue, so pull computer and have a look at connector and its circuit board
Pins 46 and 49 are signal return
Pin 26 is reference

And just a heads up
Only use Motorcraft or Hitachi brand IAC Valve for replacement, these are true solenoid valves, other brands are stepper/solenoid, so WILL cause idle issue
An old wrecking yard Motorcraft IAC valve is a better replacement than 3rd party NEW

 

[ss27gogeta]

Pulled appart the ecm and this is what I found nothing burnt but there is corrosion on the inside it looks like can I clean it up and it be ok or should I look for a new one?

 

[RonD]

Doesn't look that bad, the "spots" are from the sealant Ford sprays on after assembly its like a resin

Did you pull up on the two capacitors to make sure both wires on each is still connected

You can use isopropyl alcohol, 99% is best, to clean electronics, its a solvent but also doesn't leave a residue behind that can short out connections

The J3 connector is in the middle left of 1st picture, make sure its cleaned up, no residue on contacts or traces

 

[ss27gogeta]

Ok got everything back together and put a new o2 sensor in the truck and an egr. Drove it to work a couple days this week still have the bouncing idle issue. Also truck will start fine in the mornings but when I get off in the afternoon it don't want to stay running untill I drive it about 10 minutes kinda odd. I've also noticed the bounceing idle don't start untill I've drove the truck for 5-10 minutes. Seems like my issue might be temp related as it don't like to run in the afternoon when it's hotter and my bouncing idle do t appear until the tru k starts to warm up. also when I try to run the truck with the maf unplugged it runs way worse it won't stay running.

 

[RonD]

Replace ECT(engine coolant temp) sensor if you haven't already, it tells computer how much CHOKE to use on Cold Starts and what RPMs to idle at based on temp

The 5 volt ECT sensor is only used by computer
Dash temp gauge uses a 12volt sender

 

[ABSOLOOT LOONASEA]

I had the same problem on my '90 2.9, kept getting worse 'til it got to the point as soon as I took my foot off the gas it would die, wouldn't idle at all. I replaced my IAC (Idle air control) and it immediately cured my problem. Maybe that would work for you.