Idle Problems - Need Help!

william944.0 · #1 12-11-2012, 10:44 AM

Hi,

I have a '94 4.0L automatic with 153,000 miles. I purchased the truck about a year ago and not too long after that I noticed a rough idle on occasion. Most of the time it would idle normal, but every now and then the rpm would drop for a couple of seconds and then resume to normal.

First thing I did was replace the fuel filter. I didn't expect that to fix the problem, but it needed to be replaced anyway. It didn't fix the problem.

Next I put Sea Foam in a tank of gas to clean out excess carbon deposits through the system. That didn't fix anything.

Next I cleaned out the IAC, which was quite dirty. That seemed to fix the problem for a few weeks, but not too long after that, the rough idle started to come back.

Then I replaced the IAC with a brand new one that looked exactly like the one I took off, and now it seems to idle way too high. At start up the engine will rev up pretty high for a couple of seconds and die down slightly but will still be idling pretty high. I can tell, because when I put the truck in gear and let off the brake, it will actually accelerate up to about 20 mph (not in a normal way) without pressing my foot on the accelerator. Also, when I let off the accelator to slow down, the rpm remains fairly high and the truck doesn't want to decelerate as much as it should.

I reset the computer by disconnecting the battery for 10+ minutes, and that didn't change anything.

At this point, I'm not sure if it's something wrong with the new IAC or maybe I need to replace the TPS? Any help would be greatly appreciated, as this is becoming quite frustrating. Thanks in advance.

(note: I have not cleaned the MAF yet, but I'm not sure that would fix the problem considering the drastic difference in idling once I replaced the IAC. I really don't know, though.)

1993ranger4x4 · #2 12-11-2012, 07:33 PM

My truck does the same thing. When its cold it will idle around 2000rpms and will slowly die down and on occasion drop down to 500rpms the truck will shake. Then go back up to around 1200rpms after a few seconds, and it does the shaking at 500 also when its warm.

I used seafoam, didnt work

Cleaned the throttle body, didnt work.

Gonna do the fuel filter soon

I NEED HELP TOO, lol

1993 ford ranger 4.0 4x4

XX279XX · #3 12-27-2012, 10:37 PM

Am having the same problem, kind of, what will help?

prollynotMitch411 · #4 12-27-2012, 10:52 PM

Check air filter, an idle air control valve, may also be throttle positioning sensor. Had the same problem with a 98 contour And those all fixed it.

prollynotMitch411 · #5 01-05-2013, 05:50 PM

Did this work for any of you?

william944.0 · #6 01-08-2013, 12:40 PM

Update:

I was reading up about the EGR valve and DPFE sensor and when I went to see where they were located, I noticed that I do not have a DPFE sensor where it is supposed to be located. I attached a picture showing where it should be right under the IAC valve, and you can see where the bolt is supposed to go, yet nothing is there.

I have no idea why it doesn't have the DPFE sensor, and it makes me think this is causing the problem I've having with a high idle, but I don't know.

Also, I cannot find the EGR valve, so I'm assuming it is missing as well.

I'm pretty sure my truck is supposed to have these parts from what I've read, so why would anybody have taken them off? Also, is it an easy do-it-yourself job to install them back on?

Any help is appreciated.

Brandonhollow10 · #7 01-08-2013, 01:39 PM

It's possible it could be the throttle position sensor, but also clean your Maf sensor it helps... Goto advance auto parts and get the CRC MAF sensor cleaner cuz that thing is very sensitive any strong cleaners may damage it

dented95ranger · #8 01-08-2013, 01:51 PM

If the truck was having idle issues in the past, the previous owner may have adjusted the idle screw on the throttle assembly, along with taking off this sensor you were talking about. The thing is, with that part off, you would notice an exhaust leak from the egr exhaust tube, unless it has been plugged or removed. I had a similar issue, check out this thread for some pics as to where things should go. http://www.fordrangerforum.com/4-0-s...aust-tube.html

william944.0 · #9 01-20-2013, 08:45 PM

Update:

I cleaned the MAF, and the high rev problem persisted.

Tested the TPS, and it was working fine.

A couple of days ago I was checking all fluids and noticed the Antifreeze/Coolant reservoir was empty. Filled it up and ran the truck for a while. It emptied, so I filled it up again. Took probably close to a gallon before I didn't have to fill it up again.

For some reason, that fixed the problem. Runs perfect now. I'm not sure why being low on Coolant caused the truck to rev up so high, but I'm glad filling it up fixed the problem, at least for now.

1996xlt · #10 01-21-2013, 11:42 AM

Your coolant level was probably below the coolant temperature sensor so with nothing to heat the sensor up it was telling the computer that the engine was cold which cause it to run in low temperature enrichment mode.