96 X 4.0 Idles too high

[SA-Xplorer]

I have searched and found some great info on setting idle. 2000streetrod has a great post detailing all the steps to follow.

So here's problem. Idles too high (1000-1200RPM)

1. I enlarged the holes of the TPS and set it to 0.96V at closed. (It was 0.74V)
2. I cleaned the MAF sensor with contact cleaner
3. I disconnected the IAC and tried to set the screw out to lower the idle. Idle with the screw completely wound out and not touching the stop. i got to about 750RPM. Engine hunts a bit and runs slightly rough, but not too bad.
4. I reconnected the IAC and idle shot up to about 12-1500RPM and then settled to about 1000RPM. I dont have a scan tool yet so I used the rev counter.
5. I removed the IAC and cleaned it with contact cleaner. (Also the little "moose call" breather) I made sure it was dry before replacing it.
6. I reset the computer and started up without the IAC. Engine revs about 750RPM. Plugged in the IAC. Revs up to about 12-1500RPM and then settles back to about 950RPM.
7. The only way I can get revs to drop a bit (to about 850 ) is by pushing down on the side of the TB. forcing the butterfly a bit more shut.

One point to note is that I have done the TB mod where half of the shaft is cut away to improve airflow. I also have a Simota cone filter on the end of the standard X air intake setup.

What else can I look for?

follow up:

I went for a 20 minute drive. With IAC it was idling fast 12-1500RPM. I stopped and disconnected the IAC and it dropped to about 750RPM. I notice with A/C it is at 750 and without at about 850-900RPM.

Is the IAC really necessary? The idle is a little rough but faaarrrr more palitable than the high idle.

 

[2000StreetRod]

Vacuum leak?

If your IAC valve is good and you still have a high idle then I suspect that you have a vacuum leak and air is entering your engine that is not controlled by the throttle plate or IAC valve. While not as common with the OHV as the SOHC, members have experienced intake manifold gasket leaks. Sometimes the gasket where the EGR tube enters the intake manifold leaks. Check all of your vacuum hoses for tight connections and splits.

The IAC valve is an electro-mechanical device that is prone to failure. Often cleaning cannot correct the problem. You may need to replace it.

 

[SA-Xplorer]

THanks for the reply. I would not know if the IAC is faulty until I replace it and the fault does not go away. So I wil start by searching for a vacuum leak.

Does the IAC fulfil any other function except regulate the idle?

Thanks again

Afterthought. I noticed in one of your other threads that you had an idle issue after you installed a new filter. I have a SImota racing filter bolted on the front end of the MAF (back half of the original filter housing) and a trimmed plastic bucket around the filter to eliminate as much hot engine air as possible. Would the improved air flow mess up my idling?

 

[2000StreetRod]

unrelated

. . .
Does the IAC fulfil any other function except regulate the idle?

Not that I'm aware of.

. . .
Afterthought. I noticed in one of your other threads that you had an idle issue after you installed a new filter. I have a SImota racing filter bolted on the front end of the MAF (back half of the original filter housing) and a trimmed plastic bucket around the filter to eliminate as much hot engine air as possible. Would the improved air flow mess up my idling?

It turned out that my lean condition and startup engine speed flare were not related to the Akimota racing air filter I installed. It was the change in the weather to cooler mornings that was causing my problems (leaking upper and lower intake manifold gaskets). Sometimes excess oil on the air filter will contaminate the MAF sensor. A dirty MAF sensor results in a rich mixture at idle and a lean mixture at moderate engine speeds but you've already cleaned it.

Have you tested the TPS output over it's entire range to make sure it's not erratic? Since you enlarged the TPS mounting holes is it tightly mounted so it can't rotate?

It's not a good idea to run without a throttle plate stop. The throttle plate will stick in the throttle bore.

 

[Runnin'OnEmpty]

A couple other things to check would be the gasket on the
IAC, and the area around the throttle plate. Maybe the throttle
plate has elongated the mating holes in the throttle body,
allowing a vacuum leak...?

 

[SA-Xplorer]

I will "re-stop the plate as you suggest. I will need to order a new IAC. IN retropect, the idle seemed higher after I had cleaned the IAC than before. (1000-1200 changed to 1200-1500).

I checked for oil and there was no oil in the intake anywhere. My filter is a cloth one so no oil. I will recheck the TPS as I never really tested it properly after setting. But it is definitely solidly mounted.

I will be doing al of my gaskets soon. (Except the head gaskets) My tappet covers leak oil. Then if there are any leaks in the inlet manifold I will find it I am sure. And at the same time resolve the infernal exhaust manifold ticking!

THanks for the great input 2000!

 

[SA-Xplorer]

Maybe the throttle
plate has elongated the mating holes in the throttle body,
allowing a vacuum leak...?

Thanks for the input. I am not sure I understand the elongation though. Are you suggesting that the butterfly may not be seating and sealing in the throttle body opening properly? I had better pull it off and check. I will also check the IAC gasket as well.