I have a 5.0 Litre Injected engine with auto transmission in my F150 Long Box. about 200,000 miles on the clock. It is slow to return to idle. for instance. when I am in drive and come to a stop it is idling at about 800 or 850. If I put it in Neutral ( going for Reverse) It shoots up to about 1300 revs and stays there for at least 30 seconds or more some times. And if you go into reverse there is ofcouse a large cluck... Had it to a few mechanics. but none have fixed the problem.
2. Also the engine temp never gets past cold. and
3. The EEC warning light comes on regularly after about 15 minutes driving. Although switching the ignition off and on again gets rid of the EEC waring light. Any halp will bee very welcomed.
thanks

 

This may help. Not sure if 1989 was EFI. I have a 92 F150 Flareside which has the 4.9L I6 engine. At about 65,000 miles my truck did some similar idling. I would never get a check engine light though. I found that the mass airflow bypass valve/solenoid was sticking. This valve acts like a choke for EFI engines as it lets in more air for the vehicle to run at a higher idle and then closes after the vehicle has warmed up. Have had this also happen on a 99 Crown Vic and Expedition. I have also had this valve PREVENT the vehicle from running when first started(stuck in the closed position). If you can get your hands on a code reader or go by an AutoZone and have them read the code for you. That little part cost me about $65. It looks like a silver cylinder with 2 wires going to it and mounts to the intake usually near the EGR Valve. Its worth looking at to see if the carbon has built up in it. There is also a little green vacuum hose that goes to the EGR Valve. I was told if you disconnect it and plug it, the engine will run correctly,BUT you will get a code.
As for the temp, mine barely reaches the lower end of the scale and only goes past the mark when its summer and A/C is running or its low on coolant. Someone else correct me if I am wrong about any of this. This is what I have had happen to me.

 

Thanks 1992Flareside
I will have a look at that. good on you.

 

I think you have a bad gasket between the upper and lower intake manifold. Get some carb cleaner and spray it at the base of the upper plenum where it meets the manifold when it is acting up. If the idle smooths out, you found it. The gasket has been updated at the dealer to a gasket that won't do that again. It's less than twelve bucks. You need to ask for a plenum gasket for your make and model. Good luck.

Robbie

 

Thanks too bigbronc....
I will get the plenum gasket and carb cleaner. when I am getting the mass airflow bypass valve/solenoid. really appreciate the help. Am sick of taking it to mechanics and it comes back pretty much the same as it left. except my wallet a bit thinner...

 

Check the Idle Air Bypass (IAB). It was mentioned in the second post. It is located on the drivers side of your throttle body. It looks like this.


I've read that they can become gummed up and be stuck. The IAB is never half way open or closed. It's either 100% open or 100% closed. It's what controls your idle. When your engine is idling, it's fluttering open and closed along with your intake strokes. It's also open when your driving with your foot on the accelerator because it's prepared for you to let off the throttle, and if you do, it will automatically be open so the engine doesn't stall.

Here is what the insides look like when you remove it from the thottle body.


The PLUNGER part is what your looking for. Check to see if it's gummed up first. If not, look at everything else to make sure they are clean as well.

 

Thank you too Speed_Demon1965
I will check that and thanks for the diagram too.
was looking for the mass airflow bypass valve/solenoid last night I think I spotted the Idle Air Bypass (IAB). and decided that was it.. It looks quite easy to remove. can you tell me where the mass airflow bypass valve/solenoid is located too? . I get the feeling that all the sensors should be replaced along with the gasket between the upper and lower intake manifold..
I really appreciate the help and thanks again.

 

Either would account for a high idle. Since the idle eventually slows back down, I would lean toward the idle air bypass. No guarantee. On newer versions, the IACs, cleaning them is usually ineffective or temporary. The usual drill is to replace them. Fortunately they're cheap (kinda) and easy to replace.

 

Sorry, just reread your post. A cold engine could account for the check engine light and the fast idle. Sounds like a thermostat.

 

Actually the idle air control is actuated by the pcm on a duty cycle, or a percentage which means it is ONLY operated partially depending on what the computer dictates that is needed. At idle, it is less than 40 percent and I have never ever seen one at 0 percent (closed) or 100 percent (totally open). On your model, it can be cleaned with throttle body cleaner, not with carb cleaner. You have to take the two phillips screws out and remove the electrical portion and do not loose the black o-ring. Removing this allows you to manually operate the valve portion while spraying the cleaner in. Let it sit a while and clean out with brake cleaner and compressed air. Reinstall the electrical part, facing the right direction(note it on disassembly), and bolt the IAC back on the throttle body

Robbie

 

Oh, your truck does not use a mass airflow sensor, it used a map sensor located above the heater case on the passenger side of the engine compartment. It has a three wire electrical connector and a vacuum line attached to it. It does not have to be replaced, unless it is determined to be bad. Mass air sensors were not used on the F series until 92 and later which is a different body style than the 87 to 91

Robbie

 

There is no such thing as a "mass airflow bypass valve/solenoid". I think that was someone just making up some name, because they really had no idea what it was called.
Heck, the truck doesn't even have a mass airflow sensor! lol

The IAB is either open or closed, nothing inbetween. It doesn't even constantly stay open. The EEC sends pulses that makes the IAB flutter at a very, very high speed. The fluttering does occur during the duty cycle.

The IAB opens for starting the engine, idling the engine, deceleration, and WOT. It's there to prevent the engine from stalling when the throttle body closes. It's open at WOT so incase you quickly let off the throttle, it's already open and your engine won't stall.

Have you checked for error codes yet?

Try unplugging your IAB and see if the idle quality changes. If it starts to stumble or even stalls, the electrical part of the IAB is working. If the idle doesn't change, something is probably wrong with the electrical part of it.

 

I really appreciate the help here thank you.....
I just went and unplugged the IAB. then started the motor. It would not idle and died each time I took the foot of the gas. although the motor sounded far more "relaxed" and if it would idle I would have left it "unplugged".
I would like to check the error coded . I guess I need help there to. As i dont know how to do that.But I had it to a dynotech and it said it had codes 44 and 13 present. any ideas?

 

yawr250f I have changed the thermostat and nothing changed. I mean the temperature gauge worked exactly the same as before I changed it. ie hardly moved from cold. maybe 1/16 of an inch movement. I was thinking of changing it again . Incase the new one was faulty. what can you say?

 

this is the sensor that is located on the fire wall passenger side