2.9l v6 high idle / rough idle combo

[88Rangersuperduty]

Ok so I've been dealing with this issue on my 1988 ford ranger ( 2.9 v6 5 speed 4x4) when I start the truck cold or hot doesn't matter it high idles ( roughly 1300 to 1500 rpm) once you put it under load within 1 to 5 min of driving the truck spits and sputters ( dropping down too roughly 600 rpm or so) constant throttle in neutral for 30 seconds or so and it clears up and runs at 1300 too 1500 again with repeats of the same on a random occasion while driving ( same prosses clears it up) but does it every time on start up any thoughts?

 

[gaz]

88Rangersuperduty:

The high idle part sounds like a vacuum leak.

 

[rusty ol ranger]

Vacuum leak.

 

[franklin2]

Get the engine warmed up and then unplug the idle air control valve wiring plug on the intake. The rpms may drop. If they don't, turn the idle stop screw on the throttle back. If that is all the way back and it still idles, you definitely have a vacuum leak somewhere.

If you can control the idle with the idle stop screw, turn this screw till the engine is barely running. Then plug the idle air control plug back in. It will probably rev way high when you do that, but go ahead and drive it a couple of days and let it try to work itself out. If you still keep having problems I would pull the idle air control valve itself off the intake and see if it's gunked up. You can try and clean it out and see if it works better. I ended up getting a new one for mine, you can still buy them, but they are not cheap.

 

[88Rangersuperduty]

Issue has been resolved replaced all vacume lines with new pulled the IAC gasket was trash replaced gasket cleaned IAC put it all back together no stumble no high idle thanks for the help!

 

[rusty ol ranger]

Get the engine warmed up and then unplug the idle air control valve wiring plug on the intake. The rpms may drop. If they don't, turn the idle stop screw on the throttle back. If that is all the way back and it still idles, you definitely have a vacuum leak somewhere.

If you can control the idle with the idle stop screw, turn this screw till the engine is barely running. Then plug the idle air control plug back in. It will probably rev way high when you do that, but go ahead and drive it a couple of days and let it try to work itself out. If you still keep having problems I would pull the idle air control valve itself off the intake and see if it's gunked up. You can try and clean it out and see if it works better. I ended up getting a new one for mine, you can still buy them, but they are not cheap.

Messing with the screw on the throttle body is a bad idea under any circumstance except if youre adjusting a TPS.

@adsm08 can explain further

 

[franklin2]

Messing with the screw on the throttle body is a bad idea under any circumstance except if youre adjusting a TPS.

@adsm08 can explain further

This is a quote directly from the factory manual. "Don't touch this or else". Problem is, I doubt there is a Ford product on the planet with this screw, where someone hasn't messed with it. These trucks are old enough now, where we have to know how to adjust everything on it.

Same with some of the cars and trucks "this vehicle has a special coating on the throttle blade, no cleaning is necessary or recommended". You read that and then go out and inspect your throttle body and it has so much gook on it, it won't even close all the way.

 

[rusty ol ranger]

This is a quote directly from the factory manual. "Don't touch this or else". Problem is, I doubt there is a Ford product on the planet with this screw, where someone hasn't messed with it. These trucks are old enough now, where we have to know how to adjust everything on it.

Same with some of the cars and trucks "this vehicle has a special coating on the throttle blade, no cleaning is necessary or recommended". You read that and then go out and inspect your throttle body and it has so much gook on it, it won't even close all the way.

I get that. But that screw isnt really idle adjustment. Its TPS adjustment, the IAC soley controls idle. If you screw it in youre more less bypassing the IAC and just running it with the throttle plate cracked.

 

[Paulos]

From what I've read in Ford manuals, that screw (throttle plate stop screw) is only for adjusting the curb idle at the factory (and has nothing to do with adjusting the TPS). It's not advised to adjust it as it is not as simple a procedure as turning an idle screw on a carburetor (see the page below for the procedure). The TPS is adjusted automatically by the ECM. I suspect that if you moved that screw you may have to clear the ECM so it could re-calibrate the TPS (but maybe not).

As the Engine/Emissions Diagnostic Manual shows, only a type C TPS is made to be adjustable, and the 2.9's don't have a type C TPS. Again, the ECM does all the adjustment. I've read here on these forums that some people advocate slotting the stock 2.9 TPS to "adjust" it, but I don't see how this is doing any good without disabling the ECM's programming to adjust it automatically.

 

[franklin2]

The computer considers the throttle closed when the tps reads anywhere from .59v to 1.22v. So long as you are in that range, it's good. This is what the computer uses to put the engine in a idle fuel strategy, and also for a deceleration strategy when you lift off the throttle at speed going down the road. So what some of the others are saying, if you turn the screw so the TPS is not sending the correct voltage at idle, it will tend to mess it up.