Some Questions About my 2.5

[MrGiggles]

I bought a 98 Ranger XLT last night with the 2.5l and 5 speed.

It runs well enough going down the road, but it doesn't seem to idle right. Sometimes when you pull it out of gear, it will stumble, and it takes a little bit for the idle to settle down. It had an IAC code when I checked it before the drive home, but I cleared it and it hasn't come back.

I unplugged the IAC with the truck running and it ran exactly the same. Does this mean the IAC is not working or dirty?

It is also setting a P0171 code, and the LTFT are around 20%. I think this is caused by a vacuum leak somewhere.

I also noticed that the TPS is sitting at 16% at idle. Out of adjustment or normal?

 

[Mark_88]

Could all be IAC related...the idle should drop right down when the IAC is disconnected...so that tells you something.

You can try removing it and cleaning the insides if needed. Grabbing a spare from the junkyard might be a good idea so you can at least try swapping a different one in...although the replacement could be wonky also...and buying them new is not cheap...I priced one for my 2.5 and I think it was around $100 CAD...

I cleaned mine up while trying to solve a P0351 error that was also causing rough idle. These codes may be spot on or completely wrong...so check for vacuum leaks before you do anything...and if you can't find one maybe the previous owner was trying to fix something and left a hose off...or removed the IAC and didn't seal it properly...

 

[tomw]

Might not be a bad idea to take a look at the 'hard stop' for the throttle plate. If the PO had an IAC problem, using the stop to bump the normal idle speed is a short-term fix. It will idle higher, wherever set, but will not handle cold weather starts well, will possibly stumble and shake when the A/C comes on, etc.
I would take a look, and if it has been 'adjusted', remove the IAC, and clean out the insides with carb cleaner, and re-install. Some cleaners can affect catalytic converters, so be aware.
tom

 

[MrGiggles]

Might not be a bad idea to take a look at the 'hard stop' for the throttle plate. If the PO had an IAC problem, using the stop to bump the normal idle speed is a short-term fix. It will idle higher, wherever set, but will not handle cold weather starts well, will possibly stumble and shake when the A/C comes on, etc.
I would take a look, and if it has been 'adjusted', remove the IAC, and clean out the insides with carb cleaner, and re-install. Some cleaners can affect catalytic converters, so be aware.
tom

Thank you for the replies.

If someone came along and adjusted the hard stop, that may be why my TPS is sitting at 16%.

 

[MrGiggles]

I pulled the IAC today, it was pretty clean. I manually put 12v to each pin both ways and it just clicked but the plunger didn't move. Tried to ease the plunger up with a screwdriver and broke it.

I grabbed a new IAC from Autozone and put it on. At first it didn't make a difference or seem to be working at all. I pulled off the throttle body and looked everything over, it all seemed fine. I put it back together and it idles great, IAC is compensating for A/C and working fine.

However, when you go down the road the engine races between shifts, and doesn't settle down until you stop.

I read about the Ford TSB, and the harness has splices just before the TPS plug, so I believe it has been repaired before. The TPS still sits at 16% at idle too. Thoughts?

 

[Mark_88]

I had read somewhere while troubleshooting something on my 96 2.3 (with a 2.5 engine) wiring that the clutch interlock has some control over engine idle...as in sending a signal to the PCM during shifts...that controls the RPMs between shifts...drops them as needed.

So...not sure if I read that right but I was advised that it was "not that complicated" and maybe I was not reading things right...but it seems like a completely controlled system for engine management would need some sort of feedback to let it know that the clutch was engaged and to drop the revs until the TPS indicated that there was a need for the revs to be increased to maintain highway speed or to increase as needed.

So...could be TPS related for the high revs...or maybe clutch interlock...

The wiring diagrams for the 96 indicate there are 6 wires...and two of those are, apparently, for shift idle speed control...but I didn't play with them because I had disconnected my clutch interlock and bypassed the switch...but also experienced high idle after blipping the pedal.

I think there is more to it than just a pretty switch...

 

[MrGiggles]

Seems like it's more vehicle speed related than anything else. It idles as soon as the wheels stop rolling. Clutch position doesn't seem to matter.

Tonight I may slot the TPS screw holes and try to get it down below 10%. The throttle plate is also sticking a little, I will clean that out too.

 

[MrGiggles]

Drove it quite a bit today and the revving between shifts isn't as bad as I thought. It's barely noticeable. The idle has been fine too.

Still throwing that P0171 though, and the LTFT is around 25%.

Checked the B1S1 02 voltage and it switches very slowly and not in the range that it should. Have a new one on order.

 

[Mark_88]

Have you tried resetting the computer? Either with a code reader or simply disconnect the battery for half an hour...I would do that just to clear any lingering codes or effects of codes and let the system relearn with the new IAC...

 

[MrGiggles]

I have cleared them a couple times. PO171 always comes back.

I'm pretty sure I have a vacuum leak to some degree, just haven't figured out where yet.

 

[MrGiggles]

I shot some carb cleaner around ans couldn't find any major leaks. I did find the vacuum line for the heater valve just hanging. The valve had been bypassed with a manual one, so I just plugged the line. Hopefully this is why the A/C was switching to defrost with the engine under a heavy load.

Pulled the 02 as well, and it was original or close to it. Took a lot of work to remove and the threads galled pretty badly. Gonna run a tap through and hopefully the new one will seat.

 

[tomw]

The HVAC bleed to defrost when hill climbing or accelerating onto a highway is generally caused by a low vacuum in the intake(open throttle==low vacuum), however most have a check valve and reservoir in the vacuum system to prevent HVAC migration.
If the check valve is leaky, it won't hold vacuum. If the other vacuum lines or diaphragms have leaks, they won't hold vacuum. In either case, the vacuum provided by the intake goes away, and the things move. The last leaker is the lines them self.
It can be tested to determine that cause, or you can just try another check valve placed in the vacuum line from the engine leading off to the reservoir and/or lines to the HVAC. It won't hurt anything to add a check valve, at least I see no reason it would disrupt anything, but would just 'move' the check valve position to right there, rather than where ever FoMoCo put it originally. If the factory check valve leaks, it is just forming a 'union' function in the vacuum line, so nothing should be changed by moving the check to elsewhere.
tom

 

[MrGiggles]

The HVAC bleed to defrost when hill climbing or accelerating onto a highway is generally caused by a low vacuum in the intake(open throttle==low vacuum), however most have a check valve and reservoir in the vacuum system to prevent HVAC migration.
If the check valve is leaky, it won't hold vacuum. If the other vacuum lines or diaphragms have leaks, they won't hold vacuum. In either case, the vacuum provided by the intake goes away, and the things move. The last leaker is the lines them self.
It can be tested to determine that cause, or you can just try another check valve placed in the vacuum line from the engine leading off to the reservoir and/or lines to the HVAC. It won't hurt anything to add a check valve, at least I see no reason it would disrupt anything, but would just 'move' the check valve position to right there, rather than where ever FoMoCo put it originally. If the factory check valve leaks, it is just forming a 'union' function in the vacuum line, so nothing should be changed by moving the check to elsewhere.
tom

I will try that, thanks. The problem isn't as bad now that I capped that line, but it's still there.

I got the new 02 in and it's working normally like it should. Still setting that P0171 though. I'm going to drive it some more and see what happens.