1991 Ford Ranger High Idle

[91 blue ranger]

How do the grommets on your valve covers look?

My value covers leak if that is what you are asking

So could be throttle plate, IAC Valve, they are not closing enough, or vacuum leak

The throttle plate leaks a little air, not very much. It is better than the other one I had.
It is too windy right now for other smoke test so I will try again later.

 

[PetroleumJunkie412]

My value covers leak if that is what you are asking

The throttle plate leaks a little air, not very much. It is better than the other one I had.
It is too windy right now for other smoke test so I will try again later.

So, there's two rubber grommets on the tops of your valve covers, one has your pcv, other has your fresh air line. The grommets can leak with age.

 

[91 blue ranger]

So, there's two rubber grommets on the tops of your valve covers, one has your pcv, other has your fresh air line. The grommets can leak with age.

Oh now I understand. Not leaking there.
How much air is allowed to go around the throttle flap when it is closed?

 

[91 blue ranger]

So I did another smoke test and found that the can that has something to do with the gas fumes is leaking. The can is close to the radiator on the drivers side.

You need to turn the engine 180deg then test, turn 180deg then test, ect...........until you have turned it a full 720deg, 2 full turns
This allows smoke into all ports , i.e. if intake valve is closed very little smoke goes that way

Is this going to help? I just cant see how it will

 

[RonD]

Thats the EVAP charcoal canister, its EVAP solenoid valve should be CLOSED with key off

There will be a hose from the canister to the intake manifold, solenoid valve will be on this hose, but......................
(other hose on canister runs to the top of the gas tank)

In 1991 there may not be an EVAP solenoid, if the hose from the canister runs to a port IN FRONT of the throttle plate then no solenoid since it is using PORTED VACUUM not intake vacuum

Often the throttle body will have a port on the under side, in front of throttle plate, for the EVAP canister

"In front of throttle plate" means between throttle plate and air cleaner, which is called ported vacuum area, it has very little vacuum with throttle closed and vacuum increases as throttle opens, so kind of the opposite of regular engine vacuum.
"Behind throttle plate" means between throttle plate and intake valves, so regular vacuum, highest with throttle closed lower as throttle opens

So if canister is using Ported Vacuum then yes canister should leak smoke because its an open hose from throttle body to canister, same as air cleaner would leak smoke

Ported vacuum leak can't cause high idle.

 

[91 blue ranger]

Yes I have an EVAP solenoid. And the vacuum line runs in front of the throttle body.
Also how much is the throttle body allowed let around the flap. I had smoke ( a little bit) going around the flap ( not through the little hole in the flap.)

 

[crs.wdp]

I'm wondering how it has progressed with you 91 Ranger. I have a similar problem with 91 Ranger 4.0 auto and I'm starting to run out of diagnostics. I've done just about everything you have with no change. I don't want to hijack your thread with my problems but just thought I'd see if you were able to fix the high idle.

 

[91 blue ranger]

I got it a lot better than what it was. Did you change your IAC with a offbrand IAC? That was some of my problem. My truck still idles at 900 rpms when I unplug the IAC. But it is a lot better than when I started. I also put a different throttle body on that I got from a junk yard. That helped some to. The old TB was leaking air. If I would hold a light behind a lot of light came from around the flap. Hope this helps. If you did not try a smoke test I suggest you try it.

 

[bobbywalter]

Did you remove the throttle cable?


Cable bind does this too.

 

[91 blue ranger]

Yes I removed the cable. But I do not think it is binding. Never checked.

 

[crs.wdp]

I got it a lot better than what it was. Did you change your IAC with a offbrand IAC? That was some of my problem. My truck still idles at 900 rpms when I unplug the IAC. But it is a lot better than when I started. I also put a different throttle body on that I got from a junk yard. That helped some to. The old TB was leaking air. If I would hold a light behind a lot of light came from around the flap. Hope this helps. If you did not try a smoke test I suggest you try it.

Thanks for the response. I swapped the IAC with a made in USA Hitachi, as per one of the threads I read which mentioned only Motorcraft and Hitachi worked well on the rangers. It didn't seem to affect anything.

I did a smoke test with a cigar but couldn't find anything before I felt like I was gonna pass out, ha.

Any idea what this plug plugs into? One of the wires has continuity with the evap canister solenoid but neither has voltage while engine is running.

Thanks again!

 

[91 blue ranger]

Sorry don't know what it is. I never saw that wire on my truck. Could it be for an EGR valve of something.

 

[91 blue ranger]

Ok so it has been a while but I found part of the problem. The wires going to the VSS had rubbed together. So I taped the wires up and it helped. Now depending on the weather sometimes it idles differently. Like on humid days it idles faster. But sometimes when I let off on my gas the engine has incredible hold back and you can heard the engine holding back, kind of like a engine brake. Just thought I would tell you guys about my progress on the truck.