Only had this 98 4cyl Ranger for a few weeks and I have noticed that when the A/C is on and I am rolling to a stop with the clutch in the idle stays high for a few seconds and then today getting off the Freeway it stayed really high (like 3k) as I was rolling to a stop with the clutch in....

I guess what I am saying is that it just doesn't seem normal to stay at that high idle..... Yes eventually it does come down...Any suggestions on what the cause might be?

Thanks for your time LeeB

 

It could be the TPS that's causing the idling issue.

 

TPS? Throttle P???? S???? What is it and where is it and how do I test it?

Thanks LeeB

 

It is normal for RPMs to stay high until speedometer is under 5MPH, it lowers emissions
Also when shifting gears RPMs should hang high for a few seconds when clutch is in.

When AC is on idle will be higher, that part is normal, but 3,000 seems excessive unless that's where you were at when clutch was pushed in.
Computer knows your speed so will hold RPMs high until speed goes down, but generally for only a few seconds, maybe 5 seconds, but it will stay above 1,200 until below 5mph

TPS is throttle position sensor, but while it might cause it I would think not since it can't really "control" anything, it is a sensor.

The IAC(idle air control) valve is what the computer used to set RPMs, it is an air valve that by passes the throttle plate, like a controlled vacuum leak.
Computer adjusts this valve to set RPMs, this is what is used to hold RPMs high when above 5MPH and when shifting gears, and computer opens it a bit more to increase idle when AC is on.

They are not hard to clean, and because it is a moving part it can get sticky after a few years.

Also check throttle itself, it does have a return spring on it, this has to be strong enough to pull the throttle plate closed against the air flowing into the engine, if it gets weak the throttle can hang open even though gas pedal is released.
Lube throttle cable as well they can get sticky
If you have cruise control, that's another cable that can hold throttle open longer than it should.


And just as a heads up for fuel injection and manual trans, never coast downhill in neutral, it will cost you money.
Nice thing about fuel injection over a carb is that the injectors can be shut off for 0 fuel usage.
So if you are going downhill in gear, foot off the gas pedal and RPMs are above 1,400 computer will shut off the injectors, 0 fuel use, if you push in the clutch and RPMs drop to around 1,100 computer restarts injectors.
With a carb you did coast to save money, it's opposite with fuel injection

 

Whoa...... Thanks so much for the info.. Being the truck is new to me I'll give them all the once or twice over... It will be a learning for me.......

Thanks again LeeB

After re-reading your post, your right it was only about 5 seconds and the rest you describe hits the nail on the head......

Thanks

 

First things I would do if you have no check engine codes is to clean the MAF sensor with appriate cleaner and replace the IACV (or atleast test it if thats possible). Ebay has good ones for cheap

 

I too have a 98 4 cyl ranger. It too would have a high idle when coming to a stop sign when I would be coasting. It would stay high after hitting the brakes as well until it come to a complete stop at which time it would finally idle down to where it should be. Always have to come to a complete stop before it would correct the idle. It got to where it was losing power and wouldn't get over about 45 and it wouldn't be like that all the time but it was getting worse. Right before it started losing power and such the check engine light would come on intermittently. I ran the computer on it and it read that it was the catalytic converter. It had the idle problem for a long time before losing power occassional and the check engine light wasn't coming on in the beginning. I was fingering that it wasnt the catalytic converter causing the idle issue but figured it was a TPS or idle sensor or something causing the idle problems I was having. I wasn't having any loss of power issues in the beginning. I started thinking...well they must not have knocked the catalytic converter out cause the check engine light doesn't stay on but figured it would be a constant problem with low power if it was stopped up and surely didn't effect the idle in such a way. Without anywhere to start I figured I would check the catalytic converter. I don't have 700 bucks to replace it so I fixed it the cheapest way I know how. I cleaned it out with a rod. After doing so i didn't think it was riding right still initially but I think it was just me. That was Friday. This is Sunday 2 days later and there are no high idle problems and no more losing power so far. I hope that got it. It think it did. I don't know if you still have the ranger but that is what I did to fix my problem ranger. Good luck!!

 

 

Computer holds RPMs high until speedometer is under 5mph
Its an emissions requirement, 1995 and up