2.9 Hard to Start-Need Help!

[JJ_1975]

I have an 89 ranger 2.9 4x4 and have been having a lot of trouble getting it to start properly. Just to give some background: the truck will start on first attempt on some trys, but mostly turns over without catching.

So far I have:
- replaced a fuel pump and sending unit as the fuel pressure was down. Now fuel pressure is great
-replaced fuel filter on frame rail
- checked fuel pressure regulator (seems ok)
- injectors are working
- engine is firing
-new gas and no ice in system
- I attempted to start with idle control valve unplugged and the engine started but when I plugged back in the engine died. Cleaned idle control valve and it seems to be working (the plunger is moving properly inside from what I can see) but I seem to still have an intermittent issue.
- I placed an OBD1 unit on the compter and no codes were retrieved (code 10 & 11 only)

Also, the truck seems to start way better if I let go of the key before the engine catches, not sure if this is related or not? When the truck is running it sounds really good and there is no smoke, knocks, etc.

Does anyone have an idea of what could be going on? Any help would be greatly appreciated.

 

[shadetree]

Try replacing the throttle position sensor with a known good one.shady

 

[JJ_1975]

Thanks Shady....I tested TPS and it is ok. Anyone else have a suggestion? Could it be a slow leak in my fuel injectors that is causing loss of fuel pressure and my cylinder walls to covered in gas therfore reduced compression at start up?

 

[Hewgull]

Make sure you are getting good voltage to the coil when the engine is cranking. If not it could be excessive draw from the battery when the starter is engaged and when you let off the key the starter disengages allowing proper voltage to the coil.

 

[JJ_1975]

Ok....have been away from the Ranger for a couple of weeks and attempted to start the truck tonight. It started first turn ran for 20 seconds and then died, would not start back up.

This is where it gets odd. I unplugged the IAC valve and TPS and the truck started up every time. Once I plugged the IAC back in it would die, but once truck was warm it would remain running even when I plugged the IAC back in. Could this be a bad engine coolant temp sensor. What I thought is that the sensor could be telling the IAC (via powertrain control module) that the engine is warm when it is actually cold. Does this make sense to anyone? Anyone ever have this problem?