Learning idle question

[TheRoadVirus]

I've had a hunting idle problem in my F150 for quite a length of time. I've only had the chance to install a new IAC/TPS since she's been off the road. Now, it hasn't fixed my hunting idle issue but what I'm wondering is since I can't drive it could that be the reason it hasn't resolved itself? How long does it usually take for the computer to "re-learn" idle and such? If at all.

Could having a busted o2 sensor cause this issue? I have one to replace but haven't gotten around to it because I can't get the old one out. I need to go buy a torch or something. The other reason I've been slacking on that is because I'm going to end up replacing the headers anyways.

Thanks in advance.

 

[Bob Ayers]

First thing to do, check the voltage on the TPS (signal to ground pins) at idle.
The voltage should be between 800mV - 900mV.

If the voltage is ok, try resetting the PCM. You can do this by disconnecting the negative battery cable, and touch it to the positive battery terminal.

And if this doesn't work, you have a vacuum leak somewhere.........

 

[NeXtras]

is your compressor off? i know i had a surging idle when my compressor kicked in cause it was low on lube

 

[Skandocious]

If the voltage is ok, try resetting the PCM. You can do this by disconnecting the negative battery cable, and touch it to the positive battery terminal.

I was thinking the exact same thing.

Does it hunt for idle when you start it cold and it's still in open loop? Or only when in closed loop?

 

[d-kuzmen]

Make sure you don't have any vac leaks. Also the o2 could cause it, if it can't read the signal correctly it has no idea how it's running (rich/lean).

 

[Skandocious]

Also the o2 could cause it, if it can't read the signal correctly it has no idea how it's running (rich/lean).

Except when it's in open loop, when the o2 sensors are not being used. That's why I was curious if it still had the hunting idle during warmup, cuz that would rule out the o2 sensors as a possibility.

 

[d-kuzmen]

Except when it's in open loop, when the o2 sensors are not being used. That's why I was curious if it still had the hunting idle during warmup, cuz that would rule out the o2 sensors as a possibility.

If it's a heated o2 it may work before the truck is up to temp, once the 02 is up to it's operating temp they will read. But you are right o2's are ignored untill closed loop. I know most newer cars/trucks will go into closed loop in less than a min.

 

[Skandocious]

If it's a heated o2 it may work before the truck is up to temp, once the 02 is up to it's operating temp they will read. But you are right o2's are ignored untill closed loop. I know most newer cars/trucks will go into closed loop in less than a min.

I do believe on these older trucks, the computer status is based on the reading from the ECT, meaning it doesn't hit closed loop until it actually reaches operating temperature, as opposed to a timed interval. I'm not exactly sure how the newer ones do it, if its at all different...

I'm also fairly sure that the o2 sensor will not give ANY oxygen readings to the computer at all until the computer reaches closed loop. Don't quote me on that

 

[d-kuzmen]

Does the truck have a MAF or a MAP.???

 

[Skandocious]

Does the truck have a MAF or a MAP.???

Unless Ryan did a MAF swap (and I don't think he did), he doesn't have MAF. It wasn't offered til around 95-96 (depending on where you live).

EDIT: Just remembered that Ryan was talking about buying a MAF conversion kit. So no he doesn't have it.

As for the MAP, yeah he's got that. You're speaking of the manifold absolute pressure sensor? All these trucks have got em

 

[flareside_thunder]

Check your plug gaps on all your plugs...that way you can also check to see if they're crudded up...how old are your wires????Check the procelain on the plugs for cracks as well...probly not it but worth a shot......You can find the vacuum leak either with an unlit propane torch or ether or carb and choke cleaner...spray the latter two anywhere you like (but be specific) if the idle changes in a certain spot...voila.Good Luck man.

 

[TheRoadVirus]

Brand new MSD plug wires, coil, cap/rotor and NGK v-power's.

I honestly don't think I have a vacuum leak because this isn't a consistent thing.. it comes and goes. I'm almost positive it doesn't do it until it goes into closed loop.

 

[Bob Ayers]

Have you measured the TPS signal voltage at idle as suggested previously?
Even thought the TPS has been changed, if the throttle plate isn't sitting in the correct idle position, the TPS signal voltage will be too high.

A bad O2 sensor should throw a CEL, if it has thrown a CEL, scan the codes out.

 

[TheRoadVirus]

I don't get CEL's for some reason, I changed out the bulb and no difference. I'll check the TPS when I get a chance.

 

[Skandocious]

I don't get CEL's for some reason, I changed out the bulb and no difference. I'll check the TPS when I get a chance.

Then this is the perfect time to CHECK THE CODES!! For all you know, it's been throwing codes left and right.

That should ALWAYS be the first step in diagnosis, CEL or not.