Hi I have a 98f150 SC w/4.6. When the outside temp gets under 50 degree my idel gets rough at red lights. It kind of bucks a little, It was doing it once in a while when it was warm out,but now the temps are dropping it is constant. Drives and runs fine when moving, It does not go away after warmming up.Any help would be appreciated.I have searched the forums and have found a few things to look at.

 

First order is to check for codes that may have not lighted the CEL lamp.
If the truck has not had much maintaince, I would put plugs and wires on, clean the IAC, throttle body, Mass Air meter, clean the filter in the EVR and clean the EGR valve all in an effort to go thru and eliminate all these items as contributing to the problem.
Inspect all hoses and fittings that must hold vacuum as well as the PCV hose and valve.
It's time for all this to be attended to as a tuneup procedure.

 

Thanks for the help. Plugs and wires are around a year old (both are motorcraft). I cleanded the IAC and Mass. Went to Autozone and it had it scanned no codes.I just noticed this morning when I first started it that it would not idle untill i stepped on the gas pedal. It was around 34 degrees out. Ialso picked up a pcv valve but have not put it on.

 

Here is the general cold start and run stratigy as a reference for everyone.
When you turn the ignition to run, on the way to starting, the PCM sees and sets the values in tables, of the cold ECT and IAT.
This sets the level for extra fuel richness and IAC opening for enough air for a cold start and high idle on a cold engine as worked out by test and setup in software.
The PCM begins a timer function after the engine starts, to bring down the idle speed vs time and heating over several minutes if the oxygen sensors don't heat fast enough to take over fuel control by going closed loop
operation. This timer function is short most of the time except in very cold temperatures.
If there is a problem with the smooth control of the IAC the idle speed won't follow the stratigy.
If the ECT or IAT has a fault, this will also contribute to poor idle, stalling, poor fuel economy etc.
Plugs, wires or any item affecting the idle will be a factor and may not set a code if marginal or not lasting long enough.
An EGR valve stuck open or allowed to open by the EVR control will really cause a bad and rough idle. For example if the EVR gets water inside and freezes partially open or the filter is clogged, it will let vacuum pass to the EGR causing it to open and be the cause of major poor idle. The EVR is a 3 port device that has to let air back into the EGR for it to release once it has operated.
Once there is enough engine bay heat, the effects of frozen water quite likely disappear.
All Ford electronic control follows the same general cold engine stratigy from 1985. This kind of operation allows a driver to almost imediately do cold drive away without engine stall on a fuel injection engine when all function are working as designed.

 

What about the fuel filter? Has that been changed recently?

 

I having the same problem only it's happening on and off and in warm/hot weather. I have a 97 f150 4.6. I can go a month with it not happening then one day I can try to start and the only way I can keep it running is to step on the gas and leave it there for about 10min. This happens when the engine is cold or hot. I hate when it happens when I'm at a store or something then I need to hit the gas and hurry and put it in gear a real pain.ONce I get going the problem seems to go away until next time. It's like it's not getting enough gas or something.

 

Kraemer94.....I'm having the EXACT same damn issue with my '98 F-150 V8 4.6L.

I'll go to start up the truck, and it'll start, but would never hold the idle and kill immediately. I can hold my foot on the accelerator for 15-20 minutes and allow the engine to warm, but whenever I take my foot off, the RPM's drop immediately and the engine kills. Hot or cold day. Every day. Once I get going, the problem doesn't exist and the truck runs fine.

I've heard a lot about replacing the EGR valves and cleaning the throttle body. But I'm not a mechanic at all. 103k miles, just had the whole 100k overhaul done (new spark plugs, SP wires, battery, hoses, belt, PCV valve, fuel filter, transmission serviced, differential lubed, new brakes, etc.).

It seems that either something is stuck. Either open, shut, or clogged.

 

Bluegrass: Could you expand on what the heck the EVR is? What does that acronym stand for? I've never heard anyone talk about it on this board before.

Thanks

 

EVR is the term used for EGR Vacuum Regulator.
Under control of the PCM, it gates intake manifold vacuum to the EGR valve to open it.
It is a 3 port device that has a filter in it's cap. It has to let outside air back into the EGR diaphram area for it to close once it had been opened by vacuum.
Works like a straw in a liquid. You draw the liguid up the straw then you have to let air in to release the fluid back down.
The EVR is operated during cruise and light load and at the time the exhaust gas flow is measured by the DPFE for the famous 401/402 code test..
The device should be found right behind the power steering reservior at least on an 02. I may be located some other place on different years.

 

[QUOTE=JamesAtTECH]Kraemer94.....I'm having the EXACT same damn issue with my '98 F-150 V8 4.6L.

I will try cleaning the throttle body today. I really don't know what else to try. I will also try cleaning the MAF Sensor. It's hard to troubleshoot as it does not happen all the time. I could go two months with out it happening. It does have a ruff Idle when stoped at a light. I been searching on the internet and I see alot of people having a problem like this but no fix. My truck only has 75,000 miles on it.

 

Similar problem here as well. 97 4.6L. When it is exceptionally cold out, have to hold the accelerator down for a few seconds when starting, until the fuel injection appears to take over and then lidles like it should. Does it sound like the same problem?

 

To cododume,

Holding the throttle off 'rest' doesn't do anything.
Holding it wide open cuts the injection off for 'no' fuel. This action is used when the driver knows the engine is flooded and needs to clear the engine of fuel and gas fouled plugs.
.
You need to test fuel pressure at cold start.
The other possibility is the coolant sensor or the intake air temp sensor.
Clean the IAC and throttle body.
.
How cold start works; at key run position, the PCM fast looks at the values of the ECT and IAT and opens the IAC for more air. This tells what the starting control has to be for a cold engine or anywhere in between. This is part of the operating software program.
A fault in temp. detection or hardware for fuel delivery will not allow a hassle free cold start.

 

Bluegrass what does the coolant sensor do and where is it located?

 

I'm having a similar problem with my 2005. Sometimes it starts rough (cranks a lot), sometimes it doesn't crank, but most times it starts just fine.

Also, at idle it sometimes drops to about 500 then goes back up. It has never stalled but seems like it is going to ...

I've taken it to the dealer a few times and they can't figure it out.

 

The engine coolant sensor is an inverse temperature sensitive device that has a great influence on base fuel tables in the computer.
This is one of the sensors the computer uses to tell the whole range of temperatures for all the operating stratigies from cold start to full hot starts.
Some of the things that can go wrong are the thermostat. If the thermostat sticks open, for instance, the ECT will detect a colder average temp and run the fuel tables on the rich side and affect gas mileage.
If for example the thermostat sticks closed or the engine runs hot, the ECT will initiate a PCM response in a different way by changing fuel, and ignition timing in an attempt to control the engine to a safe point such that a code is set, the CEL lamp comes on to let the driver know something is wrong. If this goes to far, a cylinder head temperature (CHT) sensor's signal will cause some cylinder dropping in an attempt to save the engine from damage.

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For idle surge/hunting, the IAC is not being controlled by the PCM full time for whatever reason. Usually it's an IAC fault.
The IAC is "pulse" controlled against it's internal spring loaded dashpoted pintle so it results in a continiously smoothe control function since it is not a motor.
The throttle body is set to a small opening by a throttle stop and sets the min rpm the engine will idle at if the IAC fails. This setting also keep the throttle blade from sticking in it's bore when the engine cools. This is why this stop should never be adjusted unless someone has adjusted it out of spec.
The reason the idle hunts or surges is the idle speed is set in program. The crank pickup is the reference point the program uses to try to keep the idle within a tight rpm tolerence and tries to get the engine to match the program value within that tolerence. This is done by varying the IAC opening and the amount of air allowed to bypass the throttle plate.
Basicly a dealer tech should know that a hunting idle is the IAC action or a variable amount of unaccounted for air getting into the intake tract.
You must remember that the OX sensors also detect this and change fuel amount injected as another means of correcting the situation. This is a great part of the hunting that occurrs.
All areas have to be looked at or the problem never gets fixed.
Once again you are dealing with a full computer system and unless the operations are understood, the fixes can be a long time in coming except for some luck on well defined faults.
Good luck.