Rough Idle After Starting And Sometimes Dies

[RolandTrafton]

Hey Guys, so when I first start my 1987 Ford Ranger 2.9L V6 it deviates between approximately 800 RPMs and 1800 RPMs. A very rough idle indeed. On rare occasions, after watching the needle bounce up and down at about the rhythm of someone on a large trampoline, it gives up and dies.

I got the truck about a month ago so have been doing a series of small repairs/tune ups/restorations on it.

So far I have:

Put in New Spark Plugs.
Replaced Spark Plug Wires
Replace Distributor Cap and Rotor
Replaced Ignition Control Module
Replaced Ignition Coil

Replaced Radiator and Hoses
Replaced Water Pump
Replaced Water Pump Housing
Replaced Thermostat
Replaced Thermostat Housing
Replaced Temperature Sending Unit

Replaced Air Filter
Replaced Manifold Air Pressure Sensor
Replaced Throttle Position Sensor
Replaced Idle Air Control (Bypass) Valve
Cleaned Throttle Body

Replaced PCV Valve

Replaced In Tank Fuel Pump
Replaced In Line Fuel Pump
Replaced Fuel Filter

It took a few tries to get it to start last night, and then the same thing happened this morning.

The silver lining to this is that I’ve been learning a lot about how cars work, but I just can’t seem to get mine to do so. But maybe you guys can?

 

[PetroleumJunkie412]

@rusty ol ranger , @RonD

Short on time or I'd help out. I'll hop back on tonight.

 

[RonD]

Good to learn about fuel injection but can get expensive

All gasoline engines need to be Choked on cold start, in the carburetor days a plate was used to restrict air flow at the top of the carb, that's where the name for this was derived, the plated "choked" off the air flow into the carb
But lack of air is not why it helped start a cold gasoline engine
A carburetor adds fuel to the engine by air flow sucking fuel from its Jets
If you restrict the air flow at the top of the carb it creates a vacuum, lower air pressure, in the throat of the carb, which sucks MORE fuel out of the Jets, causing a RICH air/fuel mix, and thats what "Choke" means in this aplication

So the restricted air flow was not what helped start the cold engine, the RICHER fuel mix was, the choke plate was just a simple method to do this temporary Rich mix

A choke plate wouldn't work with fuel injection, no Jets, but a cold engine still needs the Rich mix to start and run for the first few minutes
So an ECT(engine coolant temp) sensor was ADDED to the engine, only used by the EFI computer so it knows when to "choke" the engine
All engines already had a temp sender for the dash board temp gauge, but it was not accurate enough
ECT sensor use 5volts, always 2 wires
ECT sender uses 12volts, often 1 wire
So not interchangeable, but they can look alike

The ECT sensor tells the computer to run a RICH mix for startup and then richer mix during warm up, computer also sets a higher idle via the IAC Valve during this warm up period

You report changing the ECT sender, but did you change ECT sensor as well?
Not choking a cold engine would cause hard starts and rough running until engine warmed up a few minutes

 

[RolandTrafton]

That does sound like one promising lead; the Temp Sensor has failed, so cold starts are getting an irregular fuel mixture not conducive to running a cold engine and thus idling erratically? Do I follow you correctly?

I just ordered a Motorcraft replacement Temperature Sensor to replace my current one with. Hopefully this will help.

In the interim period I put half a can of Seafoam fuel system cleaner into the tank and will put the other half in next week.

To top it all off. I’m still considering swapping out the fuel injectors and the fuel injector pressure regulator while I’m at it.

Does anybody else have any more theories or advice?

 

[PetroleumJunkie412]

I put half a can of Seafoam fuel system cleaner in the tank

Does anybody else have any advice?

Yes.

SEAFOAM ****ING SUCKS AND DOES NEARLY NOTHING.



Liqui moly jectron and their intake valve cleaner. I usually run at double strength, so on a half tank of fuel. YMMV.

CRC Intake cleaner spray. Only intake cleaner that still works. Prepare for SMOKE.

 

[RonD]

Yes.

SEAFOAM ****ING SUCKS AND DOES NEARLY NOTHING.



Liqui moly jectron and their intake valve cleaner. I usually run at double strength, so on a half tank of fuel. YMMV.

CRC Intake cleaner spray. Only intake cleaner that still works. Prepare for SMOKE.

Seafoam does just fine on cleaning the injectors on all my EFI engines.........................so Fight Me

 

[Dirtman]

Yes.

SEAFOAM ****ING SUCKS AND DOES NEARLY NOTHING.



Liqui moly jectron and their intake valve cleaner. I usually run at double strength, so on a half tank of fuel. YMMV.

CRC Intake cleaner spray. Only intake cleaner that still works. Prepare for SMOKE.

Water still works for intake cleaner, none of the chemicals even matter at that point. All your doing is steam cleaning. The smoke is not crap burning off, its the fluid steaming out the intake and cylinders. Seafoam works. Fight @RonD

 

[PetroleumJunkie412]

Seafoam does just fine on cleaning the injectors on all my EFI engines.........................so Fight Me

Um. So. Youre the first thats taken me up on my offer.

Just tell me when and where, God.

 

[RonD]

Um. So. Youre the first thats taken me up on my offer.

Just tell me when and where, God.

It will have to be in North Dakota and @Dirtman will be the referee

We should wait for Covid-19 to settle down a bit in the US, so any Thursday after 2025 would suit me, but we will have to check with Dirtman

EDIT:
And, pillows or pool noodles, your choice, I like to start with weapons before we get down to the hand to hand thumb wrestling

 

[Dirtman]

I do assume that in the finest tradition of ancient Roman automotive disputes, this will be a nude event?

 

[PetroleumJunkie412]

I do assume that in the finest tradition of ancient Roman automotive disputes, this will be a nude event?

YES

 

[rusty ol ranger]

That does sound like one promising lead; the Temp Sensor has failed, so cold starts are getting an irregular fuel mixture not conducive to running a cold engine and thus idling erratically? Do I follow you correctly?

I just ordered a Motorcraft replacement Temperature Sensor to replace my current one with. Hopefully this will help.

In the interim period I put half a can of Seafoam fuel system cleaner into the tank and will put the other half in next week.

To top it all off. I’m still considering swapping out the fuel injectors and the fuel injector pressure regulator while I’m at it.

Does anybody else have any more theories or advice?

Theres two temp senders. One just controls the gauge....its the one with only one plug that hooks onto a stud.

The one thats important has a more modern looking 2 prong plug, make sure youre ordering/changing the right one.

Can you get it to run long enough to get it warmed up? How does it run then?

The coolant sensor does work as ron described...however...it could also be a large vaccum leak. Possibly a stuck open EGR valve. If you use the throttle will it star running?

 

[RonD]

I do assume that in the finest tradition of ancient Roman automotive disputes, this will be a nude event?

Yes, of course, but only in the hand to hand combat, as was the tradition, nude thumb wars, as depicted in the carvings at the Colosseum in Rome

 

[RolandTrafton]

Hahaha ok ok settle down guys, no one has to go to North Dakota.

I bought a can of Liqui Molly Valve Cleaner and a can of Liqui Molly Fuel System Cleaner. I’ll put the other half of the Seafoam in this week, see if it does anything, and then try the Liqui Molly products

That should be right after I replace the temp sensor, and right before I swap the fuel injectors and fuel injector pressure regulator, which I already ordered.

I’ll let you guys know what happens and we can settle it that way.

 

[RolandTrafton]

It doesn’t have a problem getting up to temperature and then idling correctly around 900 RPMs. At that point, I’m good to go and it has never died when I’m up to temperature. My headaches exist only on a cold start.

I just started it this morning and it went up to 1800 RPMs, then after two minutes hung out around 1400 RPMS but would occasionally drop down to 1100 RPMS and bounce back up, but after five minutes and it’s warmed up it’s steady at 900 RPMs. This is an improvement from a few days ago. Maybe it’s that half a can of Seafoam Hahahaha.

Gonna put the other half of Seafoam In today, and the Liquimolly Injector Cleaner and Liquimolly Valve Cleaner in later this week. And also next week swap out the Temp Sensor, The Fuel Injectors, The Fuel Injector Pressure Regulator, and now it seems maybe the EGR Valve too.

Wow, when this is all done I should write a book on 2.9L 80s Rangers.

I’ll let you guys know how things develop and let me know if you have any more theories based on what I’m saying.