1993 Ranger 4.0 Idle Issue

[RonSerling]

Good Morning,
I have a 1993 Ranger with a 4.0 in it that I am having an issue with. First thing so you know this is a brand new long block with all the other items needed taken from the old engine. When I start it up and it is cold it runs great as it idles at about 800 rpm and has all the power you could ask for. After about ten maybe fifteen minutes it still runs great with all the power but I cannot seem to get it to idle properly. If I am driving normally and say come to a traffic light it will idle around 1600 rpm and if I hit the throttle it will come down a bit maybe to 1100. I looked thru a bunch of different Q&A's to see if they could be of help and I have done a number of things they all talked about. I put a new IAC on, I replaced the TPS and also replaced the ECM water temperature sensor but nothing seems to have eliminated the issue. I also took the MAF off and took the sensor off the housing and gave the housing a good thorough cleaning also. I have checked everything and anything for vacuum leaks and cannot find any there. After all this when I started it up it idled really high and when I unplugged the IAC it came down to normal. So I built a block plate and installed it in between the IAC and the manifold and like I said now when it is cold it idles perfectly but after it warms up it is all over the place. 16 - 1800 at times and then 900 and surging at times. Im pretty good with most mechanical things but this one has me stumped so I am asking for any suggestions or help anyone can provide !!! I hope someone may be able to give me something to work with as I need to get her smogged here soon and I am sure it will not pass with this idle issue. Any suggestions or ideas would be greatly appreciated

Thanks in advance

 

[rusty ol ranger]

First off, 800 RPM is not normal cold idle. Cold idle should be 1100 or so. Warm idle should be around 850.

Secondly, have you scanned it for codes? If not, do that.

Thirdly....are you sure the throttle isnt just sticking?

 

[alwaysFlOoReD]

IAC when unplugged will cause extremely low idle or the engine will die. I would suspect a vacuum leak.

 

[RonSerling]

Hey Rusty !! Some insight please !! I don't have a scanner for the older model vehicles but I am told there is a way to do it without. Any guidance here would be a big help !! Thanks

 

[RonSerling]

alwaysFlOoReD IAC unplugged gives her a nice smooth idle, when plugged in it jumps up to about 15 - 1600 !!!

 

[alwaysFlOoReD]

Check in the tech section at the top of every page. I'm on my phone or I would look it up and give you a link.

 

[alwaysFlOoReD]

alwaysFlOoReD IAC unplugged gives her a nice smooth idle, when plugged in it jumps up to about 15 - 1600 !!!

And that's NOT how it should behave. The fact it idles with the IAC disconnected makes me think vacuum leak.

 

[Josh B]

Somebody recommended me an OBD1 reader from online for appx $25 bux. When that came up I tried to find the link but seem to have misplaced it. I will certainly be looking soon for that link, and will try to remember your thread when I do.
Also, I don't want to get your inquiry off-track but would like to learn more about your experience with the short block

 

[rusty ol ranger]

I bought the OBD 1 reader from o reiley for 30 bucks, makes reading the codes idiot proof. Otherwise you gotta use a multimeter.

Just google "innova ford Eec IV reader"

 

[Tater Tot]

That sounds like a vacuum leak or the throttle is stuck open.

High idle is indicative of vacuum leak after MAF, especially with what happened after the IAC. Plugging/removing the IAC = less air to the engine. If you remove a vacuum hose to the engine and don’t plug it, the immediate response is that the idle will shoot up, before the computer tries to regulate it.