Another Idle Issue Thread

[bvenvert]

Hey guys

I am looking for some suggestions on fixing and idle probelm I have. I own a 91 Ranger with 4.0L that has issues with idle once it reaches normal operating temperature. When I first start the vehicle, everything works great, the truck idles fine and generally run pretty good for a now 18 year old truck.

Once it reaches normal operating temperature I run into a rough idle problem along with an erractic oil pressure gauge. If I pull up to a stoplight, the oil pressure will drop down below the normal level and start to fluctuate radically along with the low/rough idle. Once I hit the gas the oil pressure jumps right back to the normal level and the truck runs fine again. It acts like the idle gets too low to properly feed the system and therefore the oil pressure drops off.

I have read a lot of information through this forum and I am considering changing my IAC and cleaning my MAF, but I thought it might make sense to document my problem for the group, since I don't want to just throw parts at it. Not to mention that it runs fine at startup until it gets warm, which would make me think it may be a sensor that is associated with the operating temperture of the vehicle. I have read a bunch about vacuum leaks, but I would think it would occur at startup, as well as normal operating temperture if it was a vacuum leak.

Any help would be appreciated.

 

[Blacksheep Josh]

Clean MAF, clean IAC. Check for codes.

 

[bvenvert]

You mentioned checking for codes. Wouldn't it throw on a CEL if it was sending codes? It's not putting up a CEL.

I didn't mention earlier that the voltage meter also drops at normal operating temperature when I hit a stoplight. Again, it appears to be charging at a much lower rate at idle with my foot on the brake than it does while moving down the road.

 

[Blacksheep Josh]

Just because the CEL isn't on, doesn't mean there might be a stored code. I'd still check just in case.

Also, if you're having a charging issue, have the alternator tested, and possibly consider having the battery cables replaced. Mine were corroded very badly, I replaced them about 3 weeks ago, and the only problem I've had so far was when I accidnetally left my lights on overnight.

 

[bvenvert]

I pulled the MAF and cleaned it, although it looked good to the eye. I also pulled the IAC and it is pretty loaded with grunge. It has a Ford logo imprinted on the side, which would make me think it might be the original, so it could be 17+ years old. I have tried to clean it, but I can't seem to get the endcap off the unit. The plunger appears to still move freely, but the whole inside is dirty and I can't do much with cleaning if I can't get the endcap off. I assume the endcap is removeable, but this thing is solid.

I have already gone through the charging system which included a new battery and a new starter, along with reterminating my battery connections, so I know I have a solid system. I tested the battery at 12.6 volts and when operating the alternator is pushing 14.5 to the battery. Again, I think the charging issue at idle under load is based on the vehicle idling too low not the charging system. I think the idle is dropping down so low that the alternator is not turning at a rate fast enough to keep the volt meter from registering a drop. Not to mention it all works properly before the truck heats up.

I think I may just drop the $75.00 on a new IAC and see what happens. I just hope it doesn't make the problem worse! Sometimes with this old truck it seems like when you remove the dirt and grunge, you open up the system to failure on an adjacent system.

 

[Blacksheep Josh]

But did you replace the battery cables? If the cables are corroded and you replace the terminals, that's not doing you any good. Maybe you just left that part out?

Try looking at this:
http://www.explorerforum.com/forums/showthread.php?t=84220&highlight=cleaning+IAC

If it's the original, it might just be stuck on, so if you've removed the connectors and bolts you may have to do a little bit of picking at it to remove it.

 

[Four0Sport]

$75 for an IAC? wow.. where are you buying it from? thats expensive, never seen them that high.

 

[bvenvert]

Blacksheep

Thanks for the link to the IAC cleaning. My IAC looks a little bit different and does not have that black cap on the side. I thought the cap that I was supposed to remove was located on the end of the cylinder and it is made out of metal. I don't think it can be removed the more I screwed with it. The IAC in the pictures looks clean compared to mine. I decide to buy a new one and reset the PCM.

As far as the cables are concerned, I did not replace them, but I did test them and they were fine.

The new IAC was $72.98 at Autozone. Advanced wanted $76.99 but would have to order it.

Thanks for the help. I am waiting for the PCM to reset and I am going to give it a whirl. I'll keep my fingers crossed.

 

[bvenvert]

Well, I reset the computer by disconnecting the negative cable for about 30 minutes and button up the installation of the new IAC. I started the truck and took it out for a long test drive to allow it to heat up. The idle is much better and it seems to hold itself when I come to a complete stop. The oil pressure gauge, although it dips slightly and bounces around a little, it never dropped off outside of the normal zone. As a matter of fact, it pretty much stayed right in the middle of the gauge.

The new IAC seems to have helped immensely and I really can't remember the truck ever idling like it does now. I only had it out for a 15 mninute drive, so I am still keeping my fingers crossed, but all in all it looks like it was $75.00 well spent.

Thanks for all your help.

 

[Blacksheep Josh]

I believe the "oil pressure gauge" has been described in the past as kind of a dummy gauge... Meaning it'll either be active or it won't. But I guess as long as it's going you're in good shape?