93 Ranger 4x4 4.0 High Idle / Drivability Problems

[Vincenthdfan]

Hi everyone....I posted the below attached posts on another Ranger Forum but don't seem to be getting a whole lot of feedback over there. I'm really at a quandary as to where to go from here and was hoping I could find some resident experts here that I can glean some info from.

I cut and pasted the posts below:


I have a "new to me" 93 Ranger 4x4 that I bought with a leaking and slipping A4LD transmission in it.

I decided after researching the trouble prone nature of those trannies to convert the truck to a 5 speed.

I swapped everything over (to include the ECM computer from auto to standard 4x4 model), got everything done and noticed truck seemed to idle pretty high, even after being warmed up.

Side note: To be totally honest, I believe this engine run-ability/drivability issue was there before I swapped it over because it died when doing sudden stops on the way home with it too. But...it was leaking so badly, I never really got the opportunity to get to know the truck before tearing into it because it was leaking tranny fluid and slipping so badly.

On initial start, with original FOMOCO IAC still installed, it started up at 1800 rpm, dropping down to 1000'ish when warm.

I unhooked IAC wires, no change...

Installed a new IAC...whoa! Revved to 2500 rpm cold start, settled down to 1000'ish when warm.

Cleaned MAF with MAF cleaner.

Checked throttle stop screw and it was set correctly.

Carefully sprayed carb cleaner around vacuum lines, PCV Valve & hose, intake joints....no change.

With old IAC installed I can live with the idle and drivability except for when driving along on flat ground.

It acts like cruise control is set at any speed above 15 MPH. It will literally stay at 1800 RPM's at anything above 15 MPH on flat ground, foot off accelerator it just putts along on its own.

With the new IAC installed, its even worse...hauls butt above 15 MPH because idle wont settle below 2300 RPM's even with foot off pedal.

You literally have to drag the brake to slow down on level ground.

I'm at a loss here and could really use some advice if there's any out there to be had?

I've search functioned this to death, but this situation seems unique.

Oh, another thing its doing and has been since I attempted to drive it home....may, or may not be related...the speedometer is consistently reading about 10 to 15 MPH high as checked against my GPS.

I thought maybe the VSS was causing an issue with computer when driving, so I swapped it out with one from the 5 speed donor truck, still no difference there?

I'm a retired aircraft mechanic that knows my way around a wrench and a multi meter, so I can troubleshoot if pointed in the correct direction.

 

[Vincenthdfan]

So, I've been spraying copious amounts of Carb Cleaner around my hoses, fittings, joints, etc. all to no avail.

I did it motor hot, motor cold, IAC connected, IAC disconnected...no vacuum leaks detected.

I did find the airbox end of my intake tube weather checked pretty bad on the bottom, right near the MAF sensor. I taped it all up and it made zero difference.


I got looking at throttle body butterfly and thought, wonder what it'll do if I block that bleed hole in the throttle plate?

I taped it up with some heavy duty tape and whoala...it idled right down to 500 rpm with IAC disconnected and idled at 650 RPM with IAC connected!


I know that isn't really a fix, but just masking the problem by effecting air intake ratio.

My question is though...do throttle bodies wear around the perimeter of the throttle blade over a period of time?

Could that be enough to be causing this high idle issue I am experiencing?

Or is that wishful thinking?

Hate to go out and buy a throttle body and have zero change...they aren't cheap.

 

[Vincenthdfan]

I did a TPS check and it was perfectly within specs.

Then I performed a very thorough smoke test (still cant get the taste of cigar out of my mouth...yuck!!).

The only smoke I got was from the cool/warm air bimetallic disc hose going into the air box...it had a decent amount of smoke coming from it

And the shaft of the throttle body itself had some wisps of smoke coming out on the throttle cable side.

I removed the throttle body to clean and better inspect the bore for wear and as I suspected, there was a considerable groove worn into the spring side inside of the bore from the butterfly shifting to one side and rubbing it over the years.

This left a substantial gap on the other side, as evidenced even more by the amount of crud built up on the TPS side of the butterfly...it was obvious there's been a lot of airflow going through that edge.

I ordered a newly refurbished throttle body from rock auto....they offer a very reasonable exchange on them with the core deduction taken into consideration. Price wise, it comes out just a little more than a used junkyard one would cost. I'll give it a try...certainly cant hurt.

I think I will probably take the cool/warm air system out of play and just plug that part of the hose off...I'm not real convinced the liability with that system is worth the benefits.

I also found some weather checking/rubbing through areas on the airbox end of the intake tube between the MAF and the throttle body. This would certainly contribute to run-ability issues by introducing lots of unmetered air into the system before the throttle body. I'm sealing all of that up and will probably go scour the junkyards for a better one.

As far as the rest goes, I got absolutely zero indication of a vacuum leak from any other areas...especially the lower intake area. Nothing came out of the oil filler cap or dipstick, indicating the PVC seemed to be working also.

If the above items don't remedy my idle issue, I will probably just commence with a full re-gasketing of the intakes and valve covers.

 

[Vincenthdfan]

OK, new update today.

I received my newly refurbished throttle body today and bolted it on, tweaked my TPS to "in-specs" and fired it up.

Whoala...warmed up to a nice, calm idle, even with IAC connected.

New throttle body worked just as intended and the truck sounded so nice, idling down so calmly....sewing machine like.

So I can pretty well rule out vacuum leaks now.


However, there is still a glaring drivability issue.

It has to be electrical input related because it only does it when I have the IAC connected...

When I am driving along at any speed above 15 mph, the idle will not drop below 1800 rpm's....this is ONLY WITH IAC CONNECTED.

When idling along on level ground I can literally lift my foot off the gas pedal and have it act like cruise control at 25 mph.

Then, if I drag the brake I can get it to slow down (by force), and then when it hits 15 mph...bam, idle drops back down to normal.

In addition, at anything above 15 mph I can push the clutch in and watch the idle stay at 1800 rpm's....again, IAC controlled fast idle.

One thing of note also, my speedometer is consistently reading 10 to 15 mph faster than true speed when driving along anywhere (checked against GPS). No bouncing, just too fast.

I swapped in a different VSS from a different truck and it made no difference.

My question is...are the fast speedo speeds related to these fast idle inputs to the IAC?

I'm not quite clear yet on how they correlate with each other....still doing a ton of reading.


I did take the truck out with the IAC disconnected and it drove great with the idle set at about 750 rpm. Best its ever driven for me...which isn't saying too much I guess, since I have never even left my local neighborhood with yet!!

However, if I stopped too suddenly it would cause the engine to stall unexpectedly.

I'm trying to figure out a way to prevent that from happening so I can at least use the truck a little bit until I get the un-commanded fast idle inputs from happening all the time.

I sure could use some advice on how the systems correlate with each other so I can better understand what my issue might be....anybody??

Thanks!

 

[Vincenthdfan]

Hmmm...perhaps I need to post this in another section of this forum to try to get some inputs?

 

[RangerX]

Hmmm...perhaps I need to post this in another section of this forum to try to get some inputs?

I'll move it into the 1st gen section for you, under the hood section does not get as much traffic.
Sorry I can't help more than that.