My 1995 Disco has a temperamental idle issue.

The Issue:
Sometimes it will idle PERFECTLY at 750 with no issues
Sometimes it will idle High
Sometimes it will bounce up and down then stall


Some clues (ALL ARE TEMPERMENTAL):
If I am going above twenty and put the car in neutral it idles fine.
If I am going less that twenty it starts to bounce up and down in neutral.
When I come to a stop it will stall if I don't put it in neutral then hold down the gas pedal
When I press the gas pedal it will will sink a bit before revving higher SOMETIMES, other times it works great


What I have done:
New Plugs
New Wires
Replaced all hoses
Checked for vacuum leaks (THERE ARE NONE)
My fuel pressure is fine at the rail
Clean Throttle Body inside and out
Seafoam
Lubed throttle cable
ensured base idle is around 750 (according to the tach)
replaced stepper motor
using 93 octane
All new fluids



The Thing that is driving me crazy is that this is temperamental, even when the stepper is unplugged


I have no idea what to check next...

I know the dealer can set the base idle for 4.0s but I have a distributor so can someone with testbook fix it by just pressing buttons?


The one problem with the car right now is the o2 sensors are not hooked up, new ones are coming in 1.5 weeks, but I do not think this would affect idle


PLEASE SUGGEST ANYTHING THAT COMES TO MIND!

 

Hook your O2's back up.
The tach is no where near accurate enough to set your idle by, it might be idling at 550 and not 750.
Once your new O2's are in drive it for a week and then see what happens.
If it is still a problem then you will have to take it to the dealer, sorry.
It might be your vacum advance is not working properly and it is not adjusting the timing correctly.

 

the o2s were cut... I got the front of the exhaust (from cats to flanges) and they cut them on me.

Would those actually cause temperamental idling though?

Also what would the dealer do? Just hook it up to a computer and press a few buttons, or actually use a special tool to do something?


Thanks for the quick reply!

 

Well the would plug into the ECU and see the REAL idle speed, maybe press a few buttons and tweak a thing or two.
Should only take a hour so 1 hour labor should be all you pay.
But wait until AFTER your new O2's are in.

 

Your O2 sensors will cause more problems then you would think possible. The ECU looks for those signals to calculate how much fuel to dump in the cylinders, how much to advance or retard the timing and a bunch of other stuff. I would bet once you have your new O2s in your problem will correct itself.

 

"It might be your vacum advance is not working properly and it is not adjusting the timing correctly."

Can you explain this further... I'm learning as I go


Thanks for all the replies... anyone know the cheapest place to go for o2 sensors?

 

You have a distribitor and not electronic ignition.
The cam shafts turns the rotor inside the distibitor cap.
Electronic ignition allows the ECU to advance or retard your engine timing based on engine load to give you the most from your engine, it uses a knock sensor, cam sensor and crank sensor as well as the O2's.
Your truck uses engine vacum to advance and retard the timing.
The vacum moves the distribitor so that the spark plugs spark before, at, or after TDC (top dead center).
Not sure if that helps, but that is about as plain as I can put it, somebody else can add I am sure.

 

ties things together, i appreciate it

 

One thing I don't get from this is how the issue can be temperamental if my car is mainly controlled through vacuum

 

If the vacum advance hose has a small crack in it it can be tempermental.
The hose flexes one way and the crack opens up, flexs anotherway and the crack closes.
I'm not saying that is the problem, just something to look at.