97 ranger starts then dies unless I give it gas

[Rangerdanger2000]

So I just bought a 97 4.0 ranger when I got it it had an unsteady idle so I went and replaced the tps iac maf sensors and fuel pump. now it is running even worse and will refuse to stay running. I heard hissing so I replaced the upper intake manifold gasket and still the same problem. Any ideas? thanks

 

[RonD]

Welcome to TRS

Your IAC Valve is not opening

Its a simple 12volt solenoid that computer uses to set idle RPMs.

Take the IAC Valve off the intake and plug in its 2 wire connector back in
Turn on the key, engine off
Look at the valve inside IAC and unplug the 2 wire connector, you should see the valve move to CLOSED position, then plug wires back in, and it will open all the way, doesn't move much but clearly visible IF ITS MOVING

Computer gives IAC Valve full 12volts for startup, so opens it all the way, which would be about 1,800-2,000rpms
Once engine starts, RPMs above 400, computer will start to close it to set cold idle, 1,100rpms, or warm idle 700rpms, depending on coolant temp.
This is why fuel injected engines should REV on startup then RPMs will drop


Test your old one as well

 

[Rangerdanger2000]

Thanks Ron! I will definitely try testing the IAC and will let you know the verdict if that's not the problem what else could it be? Could that cause a hiss?

 

[Denisefwd93]

Everybody (but you) knows that I'm going to say check for a blocked catalytic converter/ exhaust system if you're sure you have no vacuum leaks

 

[Rangerdanger2000]

I believe there may be a vacuum leak as I also hear hissing when I rev the motor

 

[Rangerdanger2000]

any ways to diagnose??

 

[RonD]

Vacuum leak "almost always" causes higher RPMS, not stalling

You have a fuel injected engine, so there is NO gas pedal, you have an AIR PEDAL now
There is no accelerator pump like a carb had, or Jets, which gave the name to the Gas pedal, because when you pressed it down gasoline actually was squirted into the engine directly

With fuel injection when you press down the "gas pedal" you are only adding more air
The computer then adds more gasoline based in air flow


But just like on a carb engine, air = RPMs, not gasoline
If you add more gas to an engine you get a flooded engine, if you add more air you get higher RPMs

It reads like you don't have enough air to keep engine running, which is why pushing down on the "air pedal" keeps it running

These are all just guess's, you are there we are not

 

[Craig0320]

Everybody (but you) knows that I'm going to say check for a blocked catalytic converter/ exhaust system if you're sure you have no vacuum leaks

Never not once thought that nope.

 

[RonD]

any ways to diagnose??

What was the verdict on the IAC valve, is it opening and closing?

The hiss can be an exhaust leak

$20 vacuum gauge is a good tool to have

 

[Rangerdanger2000]

I ended up taking it to a local mechanic.. don't want to mess up anything.

 

[4x4junkie]

My '94 did something very similar once... (starts, then revs on it's own to about 2000RPM for maybe 3 seconds, then promptly dies if not given gas... A hissing sound was present as well).

I discovered the vacuum hose disconnected from the cruise control solenoid... Reconnected it, all is well again (maybe a rodent somehow had pulled on it? I did find some little feet-prints in the dust in that area).
So yes, a (large) vacuum leak on an EFI motor can infact cause it to stall (A/F too lean to burn, and out of range for the computer to manage it).

You would need to look for the source of the hissing noise, and go from there (should be a simple fix for a mechanic if it turns out to be something similar).

 

[Rangerdanger2000]

Although mine isn't equipped with cruise control I'm crossing my fingers that it's just something minor like that and nothing too hard to track down They are gonna let me know tomorrow. Thank you for the support!