Hey all, I'm having an issue with my 1994 2.3l 2wd Ranger. I just replaced the transmission a few days ago due to worn syncros, as well as the rear main seal, the oil pan gasket, the clutch master cylinder, and the serpentine belt. I got everything put back together, and on the first start I immediately noticed it idles rough, and sounds like it idles lower than usual too. It also takes longer to start especially on warm starts, and constantly feels like it's going to stall. However, once you get moving it drives and sounds exactly like it should.

This morning I replaced all 8 spark plugs, cleaned the MAF, throttle body, and Idle Air Control Valve, and replaced the Throttle Position Sensor with a new one I also checked all the vacuum lines, and could not find any cracks or breaks, and the vacuum hose connected to the Fuel Pressure Regulator does not have fuel in it, indicating the diaphragm inside is still good. I also disconnected the battery for 20 minutes, then reconnected and idled the truck for 20 minutes to see if it sorted itself out, but it did not. Nothing seems to help it idle correctly. The second you touch the gas though, the engine stops vibrating as much and everything evens out.

Where should I go from here? I've tried everything I can think of.

 

Welcome to the forum

Good testing and good diagnostics

The Dual spark plug 2.3l's well any Dual Plug engine has another unique way to test the spark systems
The whole point of dual sparks in one cylinder is that it adds more power, so both spark plug have to fire at the same time or there is no point in using dual spark plugs

So as a test, with engine idling unplug either coil packs 3 wire connector, disabling that coil pack, use rubber glove or insulated pliers
If you get a steady misfire or 2 on working coil pack/plugs, double check spark plug wires, the 1/4 and 2/3 firing order, easy to reverse those
2.3l Lima engines ran fine on 4 spark plugs from 1974 thru 1988, so should do that in 1994, lol

Then do the same test but using other coil pack
(you should do this test once a year, because you can never tell if one spark plug fails, you can only tell when both spark plugs fail in one cylinder, lol)

If it runs with the same roughness on either coil pack then could be the ICM but hard to relate that to transmission work
Run your hand around the top of the bell housing engine mating, I have pinched a wire or two in there when reinstalling the engine or transmission

Check PCV valve or replace it

Does your 1994 have an EGR valve?

 

Thanks for the reply.

I idled the truck and tested both coil packs by unplugging the three-wire connector, one at a time. The truck continues to idle without significant change with only one coil pack plugged in, regardless of what pack, so that seems to eliminate coil packs/plugs/wires as a problem. I will note the truck runs ever so slightly better with both plugged in, but still idles crappy. I assume that's perfectly normal considering the truck came with two coil packs for a reason.

I checked for pinched wires, and couldn't see/feel any. I was fairly careful when I installed the transmission, so I didn't figure that would be a problem, but you never know.

It does look like my truck has an EGR valve.

I saw another post somewhere about valve recess on 2.3l Ford motors, is that something common enough to be worried about?

 

Not common on the 2.3l, it was a 3.0l V6 Vulcan issue 2004-2006
But 2.3l can "tulip" intake valves
But all engines with valves can get burnt exhaust valves

To eliminate valve issues you would pull out the 4 spark plugs on exhaust side, the easier ones to remove
Then do a compression test on each cylinder
Write it down
Compare results
You are looking for a different greater than 10%
So if 3 are 150psi, 10% is 15psi
If a 4th is 130psi, then its has a problem

Compression is mechanical, and either good or bad, no grey area, so its a good test to do first, to take that off the table, or find out it IS the issue, you can spend weeks chasing spark or fuel issues especially if is not a spark or fuel issue, lol

 

I might purchase a compression test kit, and a new PCV since they are cheap and I don't have a ton of cash to throw at this thing.

An ICM seems pretty pricey at least for right now, but I may have to try to replace it down the road though.

Before then, is there anything else I can eliminate with DIY testing or troubleshooting? Seems like everyone online has a completely different solution to 2.3l idle issues and I don't want to nickel and dime myself to death with tons of new sensors/modules etc. if I don't have to.

 

Auto parts stores often rent tools or loan them free with a deposit
And tool rental paces as well
I wouldn't buy a compression tester kit unless you will spending a lot of time fixing friends and family vehicles, like me, lol

 

I have a coworker that is lending me a compression tester, so I will try that out. I will also check again for a vacuum leak - I raised up the engine an inch or two when replacing the oil pan gasket and I raised up the front of the engine when placing the new transmission, so I'm wondering if I moved the engine enough to stress a vacuum hose out and cause a crack or something. When idling the engine, I unplugged a few inconspicuous vacuum hoses one at a time and noted that the idle didn't really change... maybe that indicates a pre-existing leak? I will reply back with results soon.

 

Finally had a chance to compression test the engine, and the results are fine. Cylinders 1-4: 155, 145, 155, 145 on average. No problems there it seems. I'm convinced it is a vacuum leak, but can't find it anywhere. Might need to take it somewhere for a smoke test.

 

Yes, compression numbers are good

So fuel mix or spark
Spark is a long shot on Dual spark plug systems, since both spark plugs have to fail on one cylinder to get a spark misfire

Leaving air/fuel mix, so lower intake air leak could be the issue or dirty injector tip
If an injector drips fuel at idle levels it makes a poor mix, which is better when injectors open longer, high RPMs
Seafoam in the gas tank can help that, I add it once a year and my 4.0l idles smoother for about a year, lol

4cyl engines don't have smooth idles under 700rpm or so, they fire every 180deg so they can get shaky under that

 

I've already replaced all 8 plugs and tested the 2 ignition coils, so it's not spark. I added seafoam and drove quite a bit, but the idle didn't change. I'm really leaning towards a vacuum leak. I did the carb cleaner test, but couldn't isolate any hoses. I know smoke tests aren't always reliable, but I think that's going to be my next best bet to try to find a vacuum leak.

 

Alright, spent several more hours on this recently.
I spent quite a bit of time trying to isolate any vacuum leaks with carb cleaner, and just can't find any vacuum leaks. Decided to check fuel: connected two different fuel pressure testers to the schrader valve on the fuel rail (not at the same time lol), tried both KOEO and KOER tests and read 0 PSI constantly, regardless if the fuel pump was priming or the engine was running. Hmmm, how can this be if the engine still runs? Pulled the fuel line from the filter, primed the fuel pump, and verified fuel comes out. Tested Schrader valve on fuel rail, it squirts fuel out. Both testers read 0 PSI no matter what. I might just go ahead and replace fuel filter and pump.

 

EFI engine can not run without fuel pressure at the injectors

Some fuel pressure testers do not have a long enough center rod to push down the center pin in the schrader valve

If you have a valve stem tool, i.e. it removes/unscrews the center part of a schrader valve, you should first relieve any pressure in the system, pull fuel pump fuse and start engine, it will die when at 0psi
Unscrew the center pin, remove it, and then install the pressure gauge
Test pressure

Remember to relieve pressure again before unscrewing the tester

 

Alright, that makes sense.

 

Replaced PCV and Coolant Temp sensor today... No changes. At this point I am just throwing parts at it, lol.

 

Ok, I replaced the fuel filter and conducted a DIY smoke test using a friend's smoke machine. The fuel filter change doesn't appear to have fixed anything, but the old one did look like it was... old. The smoke test identified leaks coming from the black caps on the Carbon Canister and the black cap on the Idle Air Control Valve. I'm not sure if those are some kind of release valve, and maybe that is normal? I did not identify any leaks elsewhere after multiple tests.