Idle woes kicking my butt

[monkeydude3]

Hello all~
1994 XL 4.0L OHV 5 speed manual. Have had an idling problem plaguing me recently. When it's warming up, as in just lifting off the C on my gauge, it drops down to about 700 rpm and idles great. Once it warms up into the "normal", the idles kicks to about 900 or so. Also when it's cold and I'm accelerating, and hold my foot on the gas steady, it surges it's way up to 2500 rpm (where I then shift) and then repeat.

I'm pretty unsure of what would cause an engine to idle faster when it gets warmer. It is not overheating either.

Here's what has been done as well:

New IAC
New air intake temp sensor
New coolant temp sensor (really thought that was it)
Cleaned MAF
Plugs/wires
Injectors(all new)
Fuel pressure regulator
Fuel filter
I attempted putting in a throttle position sensor out of a properly running explorer with the same style engine... still did the same thing.

I have also tried removing the connector from the IAC... and the idle stays high, so it is not related to that.

I've come around to also suspecting my alternator. Sometimes the charging voltage is right on, and sometimes it's almost bumping the high side on the gauge. Every so often I can smell something burning that usually ends up coming from the alternator, it appears fine with no visual problems.

Can the alternator cause my idle speed to increase without it energizing the IAC?

I'm stumped. Running out of things to check. The main idea is what would cause this engine to speed up as it warms up. Usually it's supposed to taper off into a low warm idle... Very confusing, any ideas at all would be appreciated greatly. Thanks!

George

 

[IslandSport94]

One thing that comes immediately to mind is replacing the voltage regulator. This may or may not correct the idle surge, but the alternator thing is a definite maybe. Burning smell= Not good. Are you using the stock 75 amp alternator or a high output?

 

[monkeydude3]

i'm using a stock 75 amp and in the time the truck has been in the family (about 5 years) it has not been replaced. I'm thinking the engine's solution to a slightly bad alternator is kick up the pulse width, a.k.a. idle speed. Not sure though... I'l lwait for something to actually fail before I replace anything else. Gotta watch my $$$

thanks!! how much would a regulator be, and are there any places you reccomend I buy one from?

George

 

[mechanix]

Intake leaking? I would check for a intake leak. A leaking intake gasket would defentaly cause a surge or a unstable idle and poor performace. Have you taken the throttle body off and cleaned it? The little hole in the throttle plate needs to be free from obstruction. If it is pluged up the computer might have a hard time adjusting the idle. Another thing to check if the egr. I "think" 93-94 had an egr valve. If this is hanging open from a chunk of carbon or a bad egr vaccum solenoid then it would cause the same conditions you described.

To solve the intake leak some others have been able to "snug" up the bolts that bolt the intake on, others have had to replace the gaskets cause they have been sucked into the intake.

Best of luck.

Eric

 

[IslandSport94]

Voltage regulator for the 75 amp alternator is $20 at Autozone. While you're at it, pull the alternator and have them test it; it's free!

 

[ashleyroachclip]

the regulator is integral to the alternator , as in you can't replace it !

 

[monkeydude3]

oh nice!! haha. Well my EGR valve, tube, and solenoid are all new. I also replaced the DPFE sensor. I also just replaced the lower intake gaskets with new ones from ford, as well as the upper intake gaskets too. I figure I'm just going to leave it until something actually ***** out, since the only problem now is the high idle. More annoying than anything. Take care all

George

 

[monkeydude3]

more info

by the way, the idle problem started when I changed my intake setup. I put a cone air filter on instead of the air box, and it idled fast so I figured the extra air = more idle so it was fine. I went to change back to stock and then it stayed idling fast. WTF!!!! I'm getting close to putting this truck into a lake and leaving it there.

George

 

[monkeydude3]

*bump*

 

[Lloyd10977]

I know this is a dumb question but did you plug the MAF sensor back in?

 

[monkeydude3]

yup I did. Forgot one time and it let me know with a check engine light. thanks though. This is a really puzzling problemo. oh well

thanks


George

 

[TPLYNCH]

Did you reset the computer after changing the air intakes?

 

[monkeydude3]

yeah while we had it apart the battery was disconnected. And i've tried numerous times to reset it by leaving it disconnected for about 1/2 hour and then reconnecting... I get no results. During that time I usually will make a sandwich or play GTA san adreas, hehe

George

 

[lwn]

I'm having the same problem but mine is a automatic, mine really kicks up when I turn the ac on 1250 rpms in park, Idles down when I shut the ac off. Idle is inconsistant with the ac off at times.

 

[r37ribution]

I'm having a similar problem but only when the truck first starts, and its a low rough idle isu. My EGR is disabled...I'm thinkin maybe the MAF is bad??? 193,000 might do that?

 

[monkeydude3]

yeah... guys I'm leaning towards my MAF. My auto instructor just replaced his (1997 ranger, 4.0L OHV) because it was running really lean and misfiring due to it. He also had a "check engine" situation.

My theory is my MAF is STARTING to go, in that it's running it a little bit too lean and such. From what I heard and know, the MAF can screw up a lot. Also, when an engine runs lean the fuel that gets in there is smaller in amount and as a result burns a little quicker than the normal amount so that could account for a high idle. Not sure, just going on theories here. I bet I will end up tripping a CEL soon due to the MAF. Generally this truck is a headache. And gas prices suck!!!!!!!

George

 

[lwn]

Unless I have two MAF with the same problems, maf has not cured mine. Like I said mine is worse when I turn the ac on. But no matter which maf I put on out of the two it still acts the same.

 

[monkeydude3]

Hmm.... very weird. I switched the two vacuum lines around that are on the air filter box that control the warm air control valve thing. Got me wtf it's good for. Seems to have helped slightly. I do think my problems are from a carbon buildup. When I get a chance it's going to be seafoam time!

C-ya

 

[r37ribution]

seafoam? If this is what you use to clean carbon, I need to get me some...

 

[scott93EB]

cleans carbon and it's fun for the whole family. (it also sometimes puts out lots of white smoke)