Cold engine sputter/miss

Need some suggestions about how to start troubleshooting this.

'88 Ranger 2.3

The problem: the engine has a moderate to severe sputter, miss, whatever you want to call it immediately after a cold start. Seems to get progressively worse as the weather gets colder - warmer days it is not so bad.

It is very predictable - EVERY cold start, it happens, in fact on my way to work I can pick out the exact spot on the highway that it smooths out and runs better. You can literally feel it, it's like a sudden burst of power. It takes about 2 miles of driving for this to occur.

When the engine is warm it runs normally except for a very slight hesitation every 5 seconds or so and only at idle.

Other important information: The engine itself has been rebuilt and has about 10,000 miles on it. The only modification done is that it was bored 30 over stock. Brand new plugs, wires, cap, rotor, timing belt set, etc. I did not replace any sensors during the rebuild process and the timing was set to spec, whatever that is, I forget. Fuel pressure is within spec as well.

I feel like this is an ignition or timing problem, like perhaps the distributor is not advancing enough, or too far, or something. Thoughts?

IAC if it has one...

Another suggestion would be4 to get a block heater and plug it in...virtually eliminated my cold start problems when I had a carburetor...didn't even need a choke.

Short of that...you are running the TFI distributor with four plugs...right? You can put one of those rubber boots over the distributor cap and it will help immensely in cold/damp starts. I took one from a Tempo in the junkyard and it helped my starts and running issues too...

I'm pretty sure the DIS started in 1989 so that might help...

I have the 2.5 in my truck now and having cold start issues...that I've narrowed down to the IAC...but I also have a built-in block heater that I have yet to try to see if that gets around the IAC...

If the IAC will control idle speed to handle the load of an A/C compressor, and responds to power steering load, i.e., bumping idle when the steering wheel is moved back and forth, then it is not a likely candidate for problem child in this case. It works, and should bump the cold idle to above 1k when cold, and drop it back to ~750 when hot.
Check the ACT and CTS to insure the computer knows the correct incoming air and coolant temperatures. It should bump idle until the CTS indicates temp has risen above a threshold. There are tables indicating proper resistance at a given temperature in the shop manuals. Resistance changes with temperature change, and I don't remember if it is a positive or negative coefficient... so manuals are necessary. Or you can just put a VOM across the terminals and measure, heat the coolant or incoming air, and watch the meter change...
tom

I will check out the ACT and CTS, those were suspect in the back of my mind as well.

IAC seems to be working properly. Mark, correct, it does have a TFI distributor and is fuel injected. I appreciate the suggestions but I'm hesitant to think that the block heater would help at all - mainly because by "cold" I mean that the engine just hasn't warmed up. The weather can be sunny and 70, and the truck will sputter all the way down past the gas station when I leave work in the afternoon, after it's sat out in the sun all day.

This is a strange issue because it's a polar opposite of the other 2.3's I've owned, which ALL had a miss at idle but only after the engine warmed up.

ECT(engine coolant temp) sensor is on the drivers side front below intake, it has TWO wires, it is only used by the computer to set choke and idle levels, they are not expensive, $5-$8.
From your description of the problem I would change it on spec.

There is a ONE wire sender that looks similar, it is only used by the dash board temp gauge.

OK... I replaced the ECT. It seems like it might be a little better. The next few days should give me a clear picture. It has been pretty warm out lately so it's not as bad but I did get a short sputtering period at the stop light this morning. Maybe it was a fluke thing, time will tell.

I have a few spare used air charge temp sensors, I may just swap one in after I have had several days to judge whether or not the coolant temp sensor was at fault or not.

Cool! Thanks for the update...these newfangled contraptions are just a pain sometimes with all their fancy sensors and all...

I'm still learning...but I won't actually learn anything until I fix one myself...and that requires me to drive one that isn't broken until I break it or something goes wrong like what you experienced...so thanks again...

No prob, it disgusts me when I find a relevant thread for an issue I'm having...only to be left with no resolution.

I was hoping to have had the ECT swapped out sooner but I have been busy with cutting up a parts truck and some house upgrade projects. Such is life I guess, it really nags me to have a daily driver that won't get past 45mph until its weird little issue clears up.

We are currently under a winter storm warning so this will be a great opportunity to do some more testing.

OK after my drive home tonight, I am convinced that the issue is definitely not fixed. ACT sensor next.

My guess is it running lean (or rich, sometimes hard to tell), once it goes into closed loop fuel control it makes up for what's causing the problem and clears it up. I'm assuming fuel injection since I'm not too familiar with carbs... If it has EGR, if it's leaking they don't run very good with extra exhaust gas leaking into the intake, after breaking 2 different EGR valves I eliminated it on my engine... It's a pretty simple speed density system, so it's running off of the distributor to get the engine speed to drive the ignition and injector pulse and adds in the intake manifold pressure to figure out how much fuel to give it for how much load is on the engine with how fast it is turning (it also uses the coolant temp to add more fuel when it's cold like mentioned above). If it is running lean it is either running on low fuel pressure, one or more injectors is restricted, or a wiring issue. If it is running rich (like I said, hard to tell sometimes) it would be too high of fuel pressure or an injector that's sticking open some)

I would suggest running some injector cleaner

This truck is indeed fuel injected.

Is there an easy way to test the EGR valve other than simply unplugging it? I am assuming that the mechanical part of the valve is operated by engine vacuum and the electrical side just sends a signal to the computer to compensate for exhaust entering the intake, correct?

I see that they do make EGR "delete" plugs that trick the computer into thinking that the valve is there when it really isn't. I don't have a problem leaving the EGR system in the truck, or removing it, if it would actually help. Just don't want to fix something that's not broken - supposedly having a functional EGR valve helps with gas mileage slightly as well and that is important. This winter I am averaging about 17-18mpg, not bad for a 4x4 truck with larger than stock tires but every bit helps.

What gets me here is that it is so predictable. There has to be a variable here that is only present when the engine is cold and running in open loop, and to me that would narrow it down to ECT, ACT, the EGR valve, a timing issue, or possibly the ECM itself. I will get this sorted out, it is driving me nuts.

On an '88 the computer shouldn't care what's going on with the EGR, that is unless it has an EGR position sensor on top of the EGR diaphragm (my original engine had that, and I got a code for that sensor back then), if I remember right the solenoid thing that is on the passenger side fender is controlled by the computer to tell it when to go on or not.

I have successfully plugged off my EGR once while out wheeling when I broke a drivers side engine mount which broke the diaphragm leaving the EGR open all the time with a piece of a beer can... took the ol trusty pocket knife and cut a piece that would fit between the two bolts, sandwiched it between the valve and the intake, so that's an easy way to troubleshoot it...

If the EGR has a three-wire connector, it has a 'position sensor' built in that reports back to the computer. It varies resistance based on position.
If you force the EGR valve open by using vacuum on the diaphragm, or pushing from the 'outer' side of the diaphragm, engine at idle, if the valve works, the engine should stumble, and maybe(likely) stall. If opening the valve makes no difference, likely the tube/valve/pasages are plugged with carbon.
The vacuum valve solenoids on the passenger fender liner are computer operated. Vacuum is applied by one, and is held by the other(I think..its been a while). When the computer says "no more", one valve opens and 'dumps' the vacuum. The computer uses the EGR position sensor to figure out what signal to send to the solenoid valves.
Some replacement position sensors were mis-calibrated at the factory, and would report incorrect position at either extreme - fully open or fully closed - and needed some 'adjusting' to make them work properly. From memory, the computer would complain that the valve was not responding properly as the reading was incorrect.
If you plug the EGR vacuum line with a golf tee, and you have less problems, I'd check further. If you remove it completely, you'll get pinging and pre-ignition, which will kill your gas mileage. If it fails the first test - at idle above - I'd clean the passages and check further.
tom

I have some more information and have done a little bit more troubleshooting on this but still have not fixed it.

The EGR valve was stuck shut. I don't have a good one on hand so I cleaned it up and it's at least not stuck anymore, I will have to order a replacement. Unsticking it doesn't seem to have had much effect.

I replaced the plugs and wires a while back. No change

Can't find the Charge Temp Sensor anywhere under the hood, although supposedly it exists somewhere.

Also have tried another known good coil and a known good MAP sensor, and replaced most of the vacuum lines under the hood. No change

A couple other little quirks that have popped up:

If I have the truck stopped, idling, (cold or lukewarm) and rev up the engine to a little past comfortable level, without a tach I am guessing somewhere around 5500-6000RPM, and abruptly let off the gas completely - it will just slow down and die and is VERY difficult to get restarted. It also sounds different when it's cranking over, very similar to the "fast crank" sound when the timing belt breaks.

On that same note, I also discovered that when I'm driving before it's warmed up and quit doing it's thing, I can get up to about 45mph at full throttle, and if I let off the gas and release the clutch quickly (like to slow down for a turn) it will also die, hard to restart, odd cranking sound again.

Gas mileage is also way down the toilet, I am averaging between 14 and 16. The cold weather is a factor but it's abnormally bad.

My next step is replacing that bad EGR valve. Not sure what direction to go in after that.

I looked in the 85 EVTM and found an image indicating the ACT is located on the rear side of the lower intake manifold. It screws in from the back at the lower corner of the lower intake. The ECT is located 'inboard' of the upper intake manifold, sort of between the upper and the cam cover.
Off the top of my head, and from the description, I have to agree with the post that this is an 'open loop' problem. That indicates, I think, a problem with 'basic' stuff that is out of spec. Mine has a vacuum operated/modulated fuel pressure regulator. If that is dysfunctional, you'll get too much fuel(bad mpg) until the computer starts to regulate based more on the O2 sensor readings (and MAP if you have one, or MAF alternatively).
I would go back to the pressure readings, at idle, and at WOT. I'd also take a look at manifold vacuum, using a gauge, to see if there was a mechanical thing going on.
There is also a vacuum operated 'stove flap' that directs intake air source to cold external, or slightly heated from the tin 'stove' around the exhaust manifold. When 'warm', (relative) the valve opens, and bleeds off the vacuum, so the flap springs closed(no vacuum to hold it open) and allows 'cold' air into the engine/intake. Mostly that would show up in stumble when you accelerate a cold engine(I think).
You can check that the valve is closing properly with a cold engine. The vacuum line runs from the intake manifold somewhere to the bottom(more or less) of the air cleaner box. Mine has a few 'hard lines' going from the intake to the passenger side, one for this diaphragm/valve, and one to the reservoir, and one to the HVAC(I think),
tom