I have a 91' 4.9 w/E4OD tranny. When I start my truck cold it idles up just like it should but when it idles down it dies. I start it back up it idles up but when it idles down it dies. It will do this over and over. The only way to prevent this is to feather the throttle and keep the RPM's up around 1000 finally after a few minutes of this it warms up and will stay running of course when I take off it wants to die so I have to still feather the throttle.
Once the temp gets up in it, the truck runs great, idles fine and will start fine.
I've pulled the codes and everything looks good, I've also replaced the IAC, plugs, cap, rotor, wires, fuel filter.
I have duel tanks and it does it on both tanks. I've also just recently put on a EGR restrictor but I was having the startup problems before and it didn't change that (sure runs super warm though).
Does anyone have any ideas? I'm wondering if it's either the Engine Coolant Temp Sensor or the Air Charge Temp Sensor. Maybe the TPS or MAP sensor I don't know, they are not showing bad codes but who knows. Oh by the way if anyone thinks I should replace the EGR valve with a new one and take off the restrictor please say so. I'm open to anything. THANKS

 

have you tried running some injector cleaner through it?


When you say it runs super warm, how warm do you mean? If its within a reasonable temperature then the restrictor plate is fine

 

No it doesn't run "super" warm, fact of the matter the restrictor plate hasn't really caused a noticable overall engine temp change at all. I'm sure it's combusting a little hotter now with more fresh O2 but it's so slight it's not really showing much of a change on my temp gage. What I meant was when the truck warms up a little it idles and runs fine.
I've ran injector cleaner through the intake manifold and have also added it to the tank it didn't seem to help. It was worth a shot even though I've always tried to use a good injector cleaner on a regular basis anyway.

 

As a easy test remove the idle air controler and clean that out with throttle body cleaner .
Disconnect the battery when you do this - to clean any trouble codes .
The idle controler is on top of the throttle body

 

I put a new IAC on along with disconnecting the battery, still starts and runs bad when cold.

 

Next I would test the intake air charge temp sensor .
I say test but it is easier to just buy a new one - they are pretty cheep !

 

Thanks Chas I'll do that if that doesn't work I might look at replacing the Engine Temp Coolant Sensor too. Any chance it could be my TPS or maybe my MAP sensor?

 

I dont think the map sensor is bad because it would run rough at all engine temps .
Now that you mention it the intake air temp sensor is behind the heater hose on the intake manifold so you might as well do the coolent temp sensor - due to the fact that you have to drain the coolent too so that you can take the heater hose off.
Everyone is "pull the codes" happy . I firmly belive that these trucks ( the older efi trucks ) could benifit from haveing their sensors replaced . I had the map sensor act up in my truck on monday well today I replaced it because it is better safe then sorry - besides the truck has 160,000 miles on it so I think it is due !

 

I was once told by this old Ford guy that just because the sensor wasn't showing a fault code, that didn't mean the part was working right. I think I'll pick up both an Intake Air and Engine Coolant sensor after work tomorrow. Some people might say I have more money than sence (which isn't much of either) but who knows I might get lucky.
I agree with you with 13-15 year old trucks what can it hurt!

 

I agree that a bad sensor may not set a code, but Haynes shows how to test them with a multimeter so you'll know for sure without wasting any money.

 

How much did that MAP sensor run you? Did you get it from Ford or is it an after market? Also have you ever priced an EEC? Just wondering out loud. THANKS

 

Steve I agree that parts shouldnt be randomly replaced.
I replaced my map sensor tested out fine no codes and wow what a difference in the way the truck runs - Map sensor at advance auto was $47.00 .
A guy I used to work with payed $180.00 for the eec on his 1989 f150 .

 

OK I replaced the Intake Air Charge Temp Sensor and the Engine Coolant Temp Sensor today. There was a noticable buildup on the IACT sensor. I thought I'd found my problem.
I disconnected the battery and replaced the sensors. The truck is still wanting to die when starting cold. Once it warmed up a little it idled and ran great. I'm telling you this thing runs like a top when it's warm. It seems like every time I replace a part it runs better but still doesn't want to start right.
After seeing the gunk on my IACT it's making me wonder about my injectors. I might try running some more injector cleaner through the Intake manifold tommorrow and look at replacing the TPS. One is only $20 at O'Reilly's.

 

The injectors are a LOOOONG way downstream of the ACT. That buildup is coming from the PCV, and maybe a little from the EGR.

 

The only thing I was thinking -vacuum leak!-wouldn't that shop a lean condition when the codes were pulled?
I would have the codes checked again and see if that points you in a new direction . Get the map sensor tested too while you are having the codes pulled . I agree that the parts/sensors are old and should be replaced but why spend the money if you dont have to.