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1997 Ranger 2.3 and a 5 speed manual.


I'll list some info, then watch the video...


It had this condition when I bought it a couple months ago. I start the engine and it will idle smooth. I rev the engine, then it will idle and run rough. After a while it will return to a smooth idle. For example, the engine will idle smooth, accelerate through first gear and shift then it will run rough in second, third, and so on.

After driving about 20 miles or so, the engine runs fairly good and this problem almost goes away.


I get a P1443 code every time I drive it.

I get a P0303 about every 800 to 1,000 miles.

It has new plugs, wires, coil packs, oxygen sensor, and IAC valve.

The MAF voltage was within specs according to autozone's website.

Sprayed MAF cleaner = no change.

The fuel pressure is at 30 psi smooth idle, 34 psi rough idle, and it will briefly jump to about 40 psi when I rev it.

The catalytic converter sounds like it has a crack in it and it leaks quite a bit.

I sprayed starting fluid everywhere and found no vacuum leaks.



All of the following are in "closed loop":

I can unplug the throttle position sensor and it will still run just the same. Should the engine still rev with this unplugged?

Unplug the IAC valve = no change

Unplug MAF sensor = engine will idle, but will stall when attempting to rev. Small "blip" in idle when connector unplugged.

unplug coolant temp sensor = no change

unplug air temp sensor = no change

I have a ScanGauge II that I use, and it shows -40 when unplugging the coolant temp sensor or the air temp sensor. Both sensors read normally when connected.

Unplugging all of these caused NO check engine light.



The following video has 3 parts in it. You can watch the throttle lever to see what kind of input the engine has. The engine was shaking quite a bit in most of the video, but for some reason it doesn't look or sound as bad on tape as it does live. It's worse than it appears.

The first part is the engine cold and running in open loop. The engine actually dies in this segment and is very difficult to restart. Then I shut the engine off. The next part is in closed loop. The final part is the exhaust.

5.0 said:

All of the following are in "closed loop":

I can unplug the throttle position sensor and it will still run just the same. Should the engine still rev with this unplugged?

Click to expand...

I accidentally left my TPS unplugged one time. Drove (manual trans) to the end of the driveway, pulled out into traffic, ran up through the gears twice, and didn't notice anything amiss until I tried to cruise at a constant speed on a flat road (constant throttle) when it started to buck. Never threw a CEL, either.


Have you tried cleaning the IAC (pull it off, blast with TB cleaner)? Seems a long shot, and it's often just a temporary fix, but temporary would at least point you in the right direction.

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I didn't try to drive with mine unhooked, but I did rev the engine. It sounds like it is "normal" though since yours did it too.

It has a new IAC valve = no help.

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If it were mine, I'd tackle P1443 (EVAP system, canister purge) first.

The FI engines that I've worked on have a default idle speed (like 600 rpm) if the IAC solenoid (or circuit) fails; if it weren't for this default then the engine would die when the IAC solenoid is disconnected as the butterfly valve would fully close. I've seen where people have a problem with the IAC system and they've gone in and made an adjustment to the default to raise the idle to a more "acceptable" level. You might look into someone having done this to yours.

*What happens to the idle speed when the engine is warm and you turn on the A/C?

My idle speed is between 900 and 1,000 rpm all the time - smooth idle, rough idle, engine parts unplugged... it never changes.

The A/C doesn't work right now, so the compressor never kicks in. I'll have to try the switch and see what happens though.

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Ok, I had some time to mess this thing...

When the engine is missing out, I can rev the engine a little and hear pinging from the engine.

I set the engine at TDC of the compression stroke and the timing marks lined up in each inspection hole in the timing cover.

I pulled the plugs from the passenger side - cylinder 1 smelled odd and had some brown/red specs on it. Cylinders 2 and 3 both smelled like unburnt gas. Cylinder 4 smelled normal. These plugs have only 1,500 miles on them.

The engine gets a P0303 (cylinder 3 misfire code) about every 800 miles, and only when the engine is cold.

I was going to do a compression test, but I can't find my adapter to screw the hose into the spark plug holes.


Pics... Cylinders 1 through 4, left to right, of the passenger side of the head.

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Ok, about 3 months ago I gave up on the 2.3 and pulled it out to swap in 5.0 HO. I've got the 5.0 running now, so I thought I'd tear into the 2.3 to see what the problem was.

Blown head gasket, cylinder #1. The engine has basically no ring wear on it and looked to be in great shape inside. Oh well... at least I'm having fun with the 5.0!