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Cold start, won't idle, rough engine. Runs fine warm.


al4224t

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1997
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Manual
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.
 


scotts90ranger

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1990, 1997
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2.3 (4 Cylinder)
Engine Size
2.3 Turbo
Transmission
Manual
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4WD
Total Lift
6
Tire Size
35"
I was originally thinking MAF, then IAC but you cleaned and replaced those. The next things that come up are a gummy and stuck open EGR valve but it should have a flow sensor which normally shows high flow. There could still be something going on with the IAC though as it should idle about 500rpm with the IAC unplugged. I would try to temporarily block off the EGR, take a beverage can (easy to cut with a pocket knife and thin) and cut out a chunk big enough to fit between the two EGR mounting bolts on the intake manifold and sandwich it in there, see if it runs better, if it does you now know the problem.
 

tomw

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toenails of foothills NW of Atlanta
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lima bean
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2WD
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If it was the EGR valve leaking, I don't think it would improve just because the engine warmed up, which is what was reported.
A leaky intake manifold gasket could seal up as the metal expands, but is not a likely problem.
I would suggest cleaning the throttle body, the upper intake using catalyst safe cleaner. Most likely you'll find all sorts of deposits on the throttle plate and the area immedately close to it(inner diameter of intake manifold/throttle body)
Poor running when cold could be caused by lack of fuel, poor pressure, bad spritz, less than proper flow due to incorrect air temp or coolant temp information fed to computer.
A low idle could be caused by a gummy IAC.
The idle not being 'steady' could be caused by plug wires that cause misfire, or the IAC.
Given you do not get a 'cold fast idle' when you first start the engine, I would definitely take a look at the IAC. They can get gummed up over time, or fail. You should get over 1,000(close to 1200?) rpm on cold start, and the IAC should step the idle down over the next minute or two to around 750. The IAC should compensate if you turn on the A/C or turn to defrost, it should compensate if you twist the steering wheel back and forth while sitting still IF you have power steering. It should compensate if you turned on the high beams and the A/C blower, keeping the rpms steady given the electrical load. If not, remove and clean it, or replace. You replaced, but where did you get the replacement?
Did you disconnect the battery and wait for the keep alive memory to clear so the computer could re-learn how the new IAC worked?
You can possibly use propane(bernz-o-matic type torch) and a length of tubing to direct the flow around near the intake. If the idle smooths out as you pass the propane near, you have found a leak. Or, you could use a smoke machine. There may be a youtube showing how to make one using things you have around the house.
tom
 

al4224t

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Corvallis, OR
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Ford
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Manual
Thanks for the suggestions guys.

I have already cleaned out the throttle body, but I will get a new gasket for it, they are just a couple of dollars.

It certainly seems like the IAC is not doing anything still, so I will try to troubleshoot it some more. The part was a pretty cheap one from advance auto parts, and yes the battery was unplugged for a good hour or two whilst I had the throttle body off. I found this on another forum in a thread about someone else's 97 2.3 ranger:

"Did you check IAC Valve after cleaning it?
Take it off the engine and plug in its 2 wire connector
Turn key on, this sends IAC Valve 12volts and full ground, so it should open all the way, computer does this for starting the engine, which is why ALL fuel injected engines should REV on startup
Unplug the 2 wire connector, Valve should close
Plug it back in and Valve should open again
Repeat as you see fit to make sure it is working"

Is this a valid test method? If so, this would be a much easier way to check the new IAC is functioning?

I can try blocking off the EGR as well, worth checking for sure. Given the engine coolant sensors are $20, maybe it is worth replacing anyway. Most of the parts on this truck are very old...
 

al4224t

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Corvallis, OR
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1997
Make / Model
Ford
Transmission
Manual
Ok, update:

The IAC definitely works now. The engine is briefly revving as the engine starts, then will die after a few seconds without pressing the gas. Once it warmed up and settled into a nice idle, I disconnected and reconnected the IAC plug a few times. When you disconnect it, there is almost no change in the idle speed, if there is a change I can barely hear it. However, when you reconnect it, the engine suddenly idles like twice as fast for a few seconds. Then it reverts back to it's normal slower idle.

I also checked the TPS was sending good voltages using a multimeter. Seems perfect. I replaced the worn gasket on the throttle body. I am a bit concerned as the small underside hose connecting to the throttle body, does not fit very tight at all.

Also, the engine does not vary it's rev's by itself anymore. I think that may have been my fault, by previously starting the engine with my foot already on the gas. I read this is a bad idea as it completely throws off the computer system. Today, I let it start with foot off the gas, then caught it before it died to keep it going. Seemed to behave now.

I could not get good enough access to the coolant temp sensor to change it. I managed to get a wrench on it, but could only turn it 15 degrees or so, not much use. Didn't get a chance to fiddle with the EGR today either.

My thinking at the moment, is that the computer must be setting the idle speed incorrectly. This could be a number of reasons, but the temp sensor seems to fit the symptoms.
 

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