Hi all,

So I bought my ranger last week and have been trying to fix it's one big issue since. The truck is a 1997 2.3L manual.

I'll try to describe the symptoms as best I can, then I'll let you know what I've already tried. The problem is only when the engine is cold. So it is worst, when starting in a cold morning, or really anytime the truck has been sitting for over a few hours. The problem is still present, but far less severe when restarting after only 30 mins or an hour. After a few minutes, or whenever the engine reaches normal temperature, the problem completely disappears. Truck will then run and drive just fine. It will happily idle, and never stalls once it has warmed up. So this is definitely temperature related.

Symptoms:
-When you try to start the truck, you need to start with foot on the gas. It will not hold an idle at all.
-You can get it warmed up by feathering the gas pedal to keep it running. Though even with constant pressure on the gas, often the engine will be reving up and down seemingly by itself, randomly changing rpms etc.
-Once warmed up problem disappears. Though the idle sounds very slow still, it will not stall and you can drive normally.

When I bought it, it had a CEL. So I went for a free scan at parts store, threw codes for both O2 sensors and fuel mixture. Replaced only the upstream O2 sensor, since then there has been no check engine light. However, this did nothing for the problem. I have also cleaned out the MAF sensor, cleaned the throttle body out and replaced the IAC valve. NB: The throttle body was all black inside, big buildup of muck, IAC was pretty much the same. I did notice the gasket on the throttle body looked in need of replacement, was starting to crack in one place and probably is original. Anyway, replacing the IAC itself did nothing for the problem either.

So now I am thinking might be vacuum leak? Based on the state of the throttle body gasket, it seems pretty likely. I have also read the engine coolant temp sensor could be causing similar symptoms, though it seems like there are many possible causes. Just wondering if anyone has dealt with anything similar.

Thanks.

 

Engine coolant temp sensor can definitely cause issues. The engine reads that sensor and injects extra fuel when the engine is cold to get it up to temp, it also adjusts the IAC for this by about 800 rpm or so, so it dosent stall.

If it isn't getting a good signal it won't know to add the extra fuel and will stall for sure.

If you wanna know for sure, unhook it, it's right next to where the rad hose goes to the engine on top.

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Ok, so bit of an update.

I replaced the worn gasket on the throttle body, had also changed the coolant temp sensor.

Didn't seem to be make much difference, though if you disconnected IAC when running and reconnected, rpm seemed to double for a few seconds after reconnection before returning very low.

Sent into garage for a diagnosis, they didn't get very far other than saying there was a code for the IAC. I get them to change the plugs while it's there given I was sure they would be due. Guy says afterwards half of them weren't even screwed in fully.

Driving home was worse than ever, I could only figure somehow the new IAC had stopped working between me dropping off the truck at the garage and picking it up! It was so bad the engine would die when trying to park it since the power steering load was too much and it wasn't compensating at all.

So, I buy a cheap scanner tool on amazon, plug it in. The one positive: my engine coolant temp sensor is working perfectly :), read exactly the temperature I expected. No codes for the IAC, but pending codes for both o2 sensors, one code for ho2 switch something something and one code for running too lean. Surely my replaced o2 sensor isin't faulty, is it just out of range or something?

To top it all of, truck won't evens start now. Starter was spinning, but didn't seem to be able to turn the engine over and would whine. Figured battery may be low from the time in the garage, the repeated starts, and a lack of driving. Voltmeter read 12.2V with key off. Have it trickle charging in the garage at the moment.

Current plan:
-Figure out if IAC is working? Any ideas for reliable testing? This one is new, but the box it came in was so old I didn't trust it from the start.
-Use scan tool to figure out if MAF is working correctly? It can show some live data, so hopefully this will be possible.
-If MAF and IAC are good, find way to block off EGR. If it's like anything else on this truck, it's probably all blocked up and not moving.
-Replace vaccuum hoses? Most are old and a bit cracked.
-Possibly even replace upper intake manifold gasket, but not so keen on getting to this stage.

Having big regrets about this purchase, oh well...

 

What did you clean your maf with?

They are very sensitive and you should only use MAF sensor cleaner. A bad MAF can cause shutdown at idle.

IF you've had codes for running lean and it's shutting down at idle you've probably got a vaccum leak.

Vaccum leaks aren't aparant at high rpms as the vaccum is almost non existent with the throttle plate open.

Check the following gaskets and hoses....
*Intake manifold to head
*Upper to lower intake manifold
*All hoses under the upper intake manifold
*inspect egr gasket
* inspect plastic hoses on the back side of the engine that are connected to the intake manifold and travel to the egr controller and to the hvac (under the coolant res) (these get brittle and crack)
*inspect hose going from egr controller to egr valve (you can remove the hose from the top of the egr valve if you want to keep it closed, but you will get a code)
*inspect hoses going from the evap controller (drivers side at the edge of the bay)
*ensure pvc valve is properly inserted.

If you find cracks or worn parts in these hoses replace them.
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I used MAF cleaner. My worry is guy before me was running without air filter, (should have sent me running, but I was blinded by the low low price) so it may have been screwed completely by debris.

To emphasize, it will hold it's idle ok, super steady, just very slow rpm once warmed up. It's only in this period of a few minutes after a cold start it just will not idle to save itself. If you let off the gas during this warmup it dies almost immediately.

Thanks for the tips of where to look for leaks, I'll get on that.

 

Whats the Live data say the coolant temp is at after cold startup, should be outside temp, i.e. 50degF in Oregon maybe?
Then it should start to get warmer fairly fast
Computer is running in Choke Mode at this time, Rich fuel mix and high idle(1,100rpms), O2 sensor(s) is not being used
When coolant temp gets above 150degF computer will start testing upstream O2 sensor, any O2 sensor needs to be above 600degF to work, which is why they are heated, just FYI.
If upstream O2 sensor is changing voltage at least 5 times a second computer will end Choke Mode and move to Closed Loop, which means it will be adjusting fuel mix based on O2 sensor feedback, and idle level should be about 750rpms on 4cyl with manual trans

There are TWO coolant temp devices on most fuel injected engines
ECT Sensor, used by the computer only
ECT SENDER, used by dash board temp gauge only

 

It said 40, so seemed correct. Reasonably sure I have replaced the correct sensor. I suppose any O2 sensor issues are irrelevant to the lack of idle when cold, since at this stage they are not being used...

 

40deg F, not C right?there
40degC is 104degF, which would cause lower idle than it should

Yes, O2 sensors are not used until Closed Loop, and also not used at WOT(wide open throttle), just FYI

Computer doesn't have a Fuel Pressure sensor
In 1997 and older Rangers it "assumes" 30psi fuel pressure, if you only have 15psi then it would run poorly on cold start, no O2s, and then set Lean Codes when in Closed Loop, using O2s

There is a test port on the fuel rail, looks like a tires air valve because that is what it is, a schrader valve.
And can be tested using an air pressure gauge, don't test on warm engine, gasoline spray and hot exhaust are NOT a good combination, lol.
Fuel pressure is fuel pressure hot or cold
Should stay above 10psi engine off, for weeks and months
Then should go up to at least 20psi with key on
Then 25-35psi with engine running
REV engine to about 2,500rpm and hold it there for 30seconds or so, pressure should be stable, if its slowly dropping that is also a problem
Dirty Fuel Filter can cause low pressure, should be changed every 5 years




About lean and rich codes
Computers main purpose is to calculate air:fuel mix on the fly, so very very fast calculator, but slow in every other respect, lol.
It already "knows" its operating a 2.3 LITER engine, so it already "knows" how much air will be coming in at any given RPM and throttle position, the MAF sensor is there to get the WEIGHT of the incoming air
Cold air is HEAVIER than warm air, i.e. "hot air rises" because it's lighter than colder air
Higher elevation has 'thinner air" so lighter air
Gasoline air:fuel ratio is a WEIGHT RATIO, 14.7:1
14.7 POUNDS of air, to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline

Computer gets the amount and WEIGHT of the incoming air
It "knows" how much gasoline WEIGHS(it doesn't change much by temp)
Computer "knows" the size of the injectors and Fuel Pressure at each injector<<<<<
So it "knows" the WEIGHT of the gasoline added to the engine if an injector is open for say 100milliseconds(ms)

After computer opens the injector for 100ms, it looks at the O2 sensor feedback
If O2 shows high oxygen in exhaust(lean burn) it opens injector longer, 102ms next time, then 104ms, then 106ms, ect.........until O2 shows correct oxygen levels in exhaust
If O2 showed low oxygen(rich burn) then computer would go the other way, 98ms, 96ms, 94ms until oxygen level was correct

This only takes a second or two, engine is never actually running Lean or Rich
The Codes are set when computers calculation are 20% off for any length of time
So in above example if it reached 120ms or higher for any length of time computer would set a Lean code to notify driver of the problem
A vacuum leak means computer is not getting good data from the MAF sensor, unreported air is coming in, so its fuel calculations are off, light
Same for low fuel pressure, light, because less fuel is flowing into engine when injector is open for 100ms