hey guys my 90 f250 is having a really bouncy idle and stalling issue. if you stay on the gas just enough to keep it running, itll bounce from about 500 rpm to 1500 give or take a little. seems like a pretty big jump to me. i replaced the TPS and nothing. i pulled the codes and got 21, 24, and 84. i think 84 is the issue but tell me what you think. i think 84 is "EGR vacuum" or something along the lines of that. what could be the problem?

 

i have a broken EGR vacuum line but it never surged and its been broken for a while.

 

I would replace the broken vacuum line and check for other vacuum leaks

I replace all of mine with I think 5/32'' hose

 

anybody have a diagram for the vacuum lines?

 

anybody? its not surging quite as bad now but it wont idle and its running like ****. any help

 

You should have a VECI label on the radiator support to show the basic vacuum line routing.

 

decided to check the fuel pressure and its reading 0 fuel pressure. replaced the fuel filter and its running smoother but still bouncy idle and still 0 fuel pressure. any ideas?

 

Well it won't run with 0 fuel pressure, so I suspect your gauge is not making proper contact with the schrader valve.

It's important you get all vacuum leaks fixed before we try figuring out the issue.

As far as the vacuum lines go, they're pretty simple, and IIRC, they were the same from 89 to 96.

 

ok well I guess I'm back to square one. I took care of the major vacuum leaks, the idle is still bouncing. It smooths out after holding the pedal for a few seconds but still not right. Let off completely and it dies. Only throwing the 84 code but my EGR has been disconnected for a while so i would assume thats why. Anybody?

 

There are various vacuum reservoirs on these trucks. The on one the passenger side fender well (yours may be plastic), the HVAC system on the blower box (usually hidden under insulation and a third behind the driver side headlight if you have speed control. If you have speed control there is also the associated vacuum lines and dump valve above the brake pedal.

Any and all may be contributors. Don't forget the vacuum brake booster, the IAC can leak internally or at the gasket. The same can be said for the intake gaskets.

Did you plug the vacuum line going to the EVR and EGR valve?

Plenty of things to check and it could all boil down to a sticking or faulty IAC but eliminating the vacuum leaks will increase performance and prevent other issues.

 

If it does completely when you let off the throttle, I would suspect a failing IAC valve, or an EGR valve that is stuck open a bit.

 

Subscribing, just because any idle issues on 460's always interest me.

 

well the truck is still sitting in my yard haha. if i sit there and "wiggle" the throttle just right it will stay running and actually run pretty smooth. i thought that might be a sign to narrow it down but not sure. the egr is broken so i took it completely off but i covered the hole with tape just to see if it would help and nothing. thats the only place i could think of that would be leaking vacuum. what else could this be? im stumped

 

You say you replaced the TPS. How far have you driven the truck since replacement? It might take several cycles/miles.

 

Remove the Throttle Body.

Ensure the gasket is secure and not damaged.
Look closely at the blades in the bore and check for daylight.
If daylight is present, chances are HIGH the bores are worn and creating a vacuum leak. If the Throttle stop screw has been tampered with, make a visual note or either with a scribe or marker and make a reference point and then count the number of turns it takes to close the blades fully. If daylight is still present, bores are worn.

Other problems with the Throttle Body would be worn shaft/bushings allowing for vacuum leak.