View Full Version : 2.3L Ranger engine surges when coasting

Sep 28 2011, 01:30pm
First time posting to this forum. Hopefully someone has an answer for this.

I have an '89 Ranger, 2.3L A4LD tranny, with a curious problem, that I can't pin down. At least not well enough to start throwing money I don't have at it.

It only does this when the engine is at operating temperature. Never when its 'cold'. So it normally takes a few blocks for it to become evident.

I usually drive in town, so notice this often. It starts fine, and drives fine, but when letting off the gas to coast to a stop, if and only if im between 25 sand 35 mph, the idle revs, or surges, about 200 rpm form idle, for a few seconds. If im going over 35, and coast to a stop, it'll rev at 35 mph for a few seconds, and then settle down. At 25 it'll do the same thing, and then settle down. (like: vrrom vroom vroom vroom... for some times just a few revs, sometimes its 10-15 seconds of it)

I don't know if this is a idle problem, or a transmission problem. Seems to me that the tranny is going through shift points at 35, 25, and even 15, and 5, or so, but it never revs below 25 mph. Maybe just a little blip of the throttle at 15 and 5. Is the 'blip' not working at 35 and 25, so it does it over and over again?

I've had people suggest the IAC is the culprit, and I've cleaned it really well a couple times. Possibly related is that idle, in drive, seems quite low, maybe almost 500. Sometimes it'll settle out a little higher, and smoother, but if I idle at a stoplight or something, inevitably, it'll slowly get lower and lower rpm, until it hits just above 500, and feels like its hitting on 2 cylinders. Give it some gas, and it runs fine again, till the idle comes down.

Also suggested was the MAP sensor, or IPS. Im not sure enough about any to spend the $100 or so for any given part.

Trying to think of anything else, relevant.... The truck as 228K on it. The motor had the block and head replaced with a used (w/ 50K) at around 175K.

Sep 28 2011, 05:27pm
No intake leaks anywhere?

Sep 28 2011, 09:04pm
No intake leaks that are obvious, anyway. It all started when I brought the truck home from my mom's place, in eastern ND. Im in Western MT, and an elevation change of about 3000 ft.

Would an intake leak be evident only at operating temp? Maybe if it had to do with expanding metal, I suppose....

I never did get around to spraying brake cleaner or something around vacuum lines, but I did have a friend with a vacuum gauge plug into the little vacuum distribution block between the intake and brake booster, and it was all normal and stuff.

Sep 29 2011, 10:57pm
Your truck also has a throttle position sensor, in addition to those other sensors. My bet is, THAT is your problem. The contacts on the potentiometer in the sensor are probably worn out, as most of the time, the throttle position is "at zero" putting way more wear at that point.

Fairly cheap part (first result on google, i don' buy there, never even heard of the joint)
Acdelco 213-848 Throttle Position Sensor~1989 Ford Ranger 2.3l (http://www.oehq.com/acdelco-parts_213-848_ACD_ACDelco-Throttle-Position-Sensor~1989-FORD-RANGER-2.3L.htm#)

Its also easy to test. This article doesn't explain how to do it very well, but it does basically diagnose the problems you are describing.
Symptoms of a Bad Throttle Position Sensor (http://www.buzzle.com/articles/symptoms-of-a-bad-throttle-position-sensor.html)

If you want to get really technical and know where to put your voltmeter and stuff to test it...
The Ford Ranger Throttle Position Sensor (http://www.therangerstation.com/Magazine/winter2009/throttle_position_sensor.htm)

Sep 30 2011, 09:51am
Fairly cheap part (first result on google, i don' buy there, never even heard of the joint)
Acdelco 213-848 Throttle Position Sensor~1989 Ford Ranger 2.3l

Thats cheap enough to throw money at, I'll try that, I think.

Sep 30 2011, 11:13am
You 'd think that if the TPS were at fault, and why I discounted it before, is that it only happens when at operating temp. Why would it only happen at operating temp? Does the EEC-IV pay more or less attention to the TPS when at operating temp?

Sep 30 2011, 05:44pm
My guess is, while the FI system is running on a cold engine it is in closed loop mode which may or may not ignore signal from the tps. It's worth a shot to at least test the darn thing.

Nov 16 2011, 06:01pm
A new TPS did the trick. Still idles a little low, down around 500 rpm in park, and drive. In fact I find myself holding an idle with the gas pedal at stoplights a lot.
How is this adjusted? maybe a new thread for that.

Nov 18 2011, 10:11pm
I would try a new IAC if you've already cleaned it and it didn't work. But you'll probably want to test it first. Ford Explorer Ranger Enthusiasts "Serious Explorations" - View Single Post - 91 explorer high idle (http://www.explorerforum.com/forums/showpost.php?p=2012577&postcount=5)

Worst case scenario you can push the plunger to the "open" setting and then leave it disconnected, but it will act as a vacuum leak while the truck is running normally.

Nov 19 2011, 09:29am
finally order a IAC. I was hesitant to get one before, since I wasn't sure enough that it was the problem to throw $100 at it. But I found an inexpensive one at rockauto, so its on its way now.

Also a PCV valve. Being difficult to find on the truck, I don't think its ever been changed.

Nov 20 2011, 09:19am
I hope you are testing these parts like they're suggesting. It will save you a broken heart later.