Hey guys,
Hoping someone can help me with some basic questions. I have a 5.0 in a '94 supercab. When the truck is cold it starts fine...runs at high idle until it is warm. When the truck is warm it needs to turn over excessively before it starts and when it does it goes to about 1000 rpm and then drops back to almost stall at about 350 then it goes up to approx. 500-550 rpm. It is not giving any codes, and at great expense the MAF, O2 sensor, plugs, wires and distributor were changed. (It was doing the low idle thing on occaision before all of that work) With all that I have read I am suspicious of the Idle air control (IAC) valve, the EGR ports and the throttle body. I have taken off the IAC...I can see in it, I have a can of cleaner and would like to know how to clean the it? (just spray in ther an wipe with a paper towel?
I am also interested in cleaning the EGR. It has a big rusty bolt on the bottom and then two bolts to the engine/throttle body. Do I need to remove the throttle body and the big rusty bolt on the EGR...basically I think I have identified the things I just need to know what to remove and were to remove it?
Many thanks.
boatdude

 

One more detail. Sometimes as I am exiting a highway the rpms go very low and on rare occasion it stalls at that time.
Thanks.
baotdude

 

That big rusty bolt under the egr is a tube foe exhaust to flow through. On a 94, when you try to move the nut, the tube will more then likely break, so if you do decide to clean it, use LOTS of penatrating oil. while the truck is running, if you spray the egr valve with carb cleaner and the engine changes rpm, you would more then likely have a bad diaphram, it would need a new valve. If you have a vaccume pump, attach it to the vaccume port on the top of the valve (engine running) and apply vaccume, the engine should stumble. I don't think that is your problem. I would look to fuel pressure or injectors. It kinda sounds like the engine is running rich. Having read through you second post, you migh want to check you throttle hard stop, I belive that it should idle at 750 or so. And the voltage at the throttle position sensor should be roughly .9 volts.

 

I agree that it sounds like a fuel problem like a sticking injector. But you said it stalls coming off the highway whcih is consistant with a sticking egr valve. If you want you can just leave the egr valve on the vehicle and disconnect the electrical connector for the vsv and drive it for a few days to see if the truck stops acting up. I wouldn't recommend leaving it disconnected permanently but if it's just for a day or 2 for testing purposes it will be fine.

-Jon

 

My 93 5.0L does a similar thing only when it is restarted warm it runs low and rough. Put your foot on the gas and bring the revs up to normal or slightly above and engine is still very rough. After a couple of minutes it levels out for the most part (never perfect).
The other thing it does although I don't know if it's related or not is I can drive home from work (15 miles or so) and put the truck in park and it revs to 1200 or so then gradually drops to normal. Once this has happened it will be normal until the next cold start. Seems like a vacuum leak but it's been checked. Also EGR was temporarily blocked off with no change and is now hooked back up. I think the next step may be to pull and check the injectors. I built a test bench to flow and leak check injectors.