Extremly High Idle

[PlumCrazy]

I have a 95 Ranger with a 4.0 OHV. When I start it up it will idle at 2000 rpm for about 15 min. After I drive around a little bit it will drop to 1300 rpm. It doesnt drop any further if I rev it a little either. Every now and again it will idle rough when I first start it then it will clear up, when it does this it throws a p1120. The code is for the TP sensor, so I replaced it, but it is still doing it. I have now replaced the TP sensor, IAC, swapped out the Throttle body. Then today it was idling at at 2000 it started to go up to about 3000 then dropped to 2000 agian

If anybody has any suggestions let me know.

-plumcrazy

 

[BlackBII]

Well, air has got to be getting in the motor somehow, either by the Throttle body, IAC or a vaccum leak. You need to start eliminating them one by one.

Unplug the IAC, does the idle go down?
Is the butterfly shutting all the way on the TB?
Have you checked for vaccum leaks?

I'm currently having a similar issue. Turns out my throttle cable is sticky and is not returning all the way, keeping the butterfly open slightly.

 

[PlumCrazy]

Will the IAC close by default if unplugged?

 

[BlackBII]

Yeah, it should close completely, and your truck should die.

 

[PlumCrazy]

Welp, If i unplug the IAC it doesnt die, but the idle goes down a little. I pulled the IAC off and looked down into it. It doesnt close all the way when its unplugged. So I thought that had to be it. I went and got another one. I looked down into it when I took it out of the box, and it doesnt close completely either. I put it on and the idle was the same, when I unplug it it goes down a little but doesnt die. I also checked the butterfly valve in the throttle body to make sure it closes all the way, and it does.

I think I can hear a huge vacuum leak, but Im not sure if its just the sound of the air inside the intake or not. This is my first 4.0, and I am not sure if the air in the intake is just that noisy. My 2.3 is pretty quiet. I sprayed a little intake cleaner around the intake gaskets and vaccum lines to see if there was a leak big enough to suck a little in and raise the rpm's, but no dice.

I found out one more nifty little fact though. I had an new in the box TP sensor left over from my GF's 96 2.3 Ranger. When I first found out the p1120 was for the TP sensor I put the new one on. I was double checking part numbers today and found out the TP sensor for the 2.3 has a different part number than the 4.0. Even though they look the same, there is something diff inside. And of course they didnt have the 4.0 TP sensor in stock, so I will have to investigate further tomorrow to see if thats my prob.

If all my new sensors and dont solve the problem, then I am going to pulle the intake off and replace the gaskets/re torque all the bolts. Since I have heard the lower intake bolts have a tendency to back off a little. But I dont seem to have an oil loss issue, nor is there and oil leaking anywhere.

-plumcrazy