Head scratcher need some brains picked...

[Tattmann]

Hey all, I've got a 92 explorer 4.0 5speed manual trans that has started something strange. The idle has gone wonky. It is idling up to 1800 rpm's. Coasting in neutral is the same, 1800 to 2000 rpm range. Now wait, before everyone jumps on the vacuum leak bandwagon, hear the rest. I know this would usually mean a vacuum leak. I can not find one. Can't hear one anywhere, can't make one show up with starter fluid. However, here comes the kicker, when I press the clutch in for 4 or so seconds, the idle drops down to normal 1000 rpm's every time. The idle control valve seems to be working normally, I unplugged it and it dropped idle way down, then it went back up when plugged in. From what I've read that seems to be normal. Does anyone have any ideas on this one?

 

[smegun]

jammed throttle linkage / rev limiter cuts back R's ?? you can unplug the tps lose economy from what I here

 

[Tattmann]

Thanks for replying, but the throttle linkage and cable are all free. Tps should be good, have not replaced it yet but I have a new one.

 

[Roadrunner777]

This reminds me a little bit of a Mass Airflow Sensor problem, but the change with using the clutch is a odd. I might look at that, clean it, measure voltages. Not definitive, but it's easy, and it's never a bad idea to clean an MAF... fast and easy.

 

[94Sport5]

When I removed my iac and cleaned it to see if it would make any difference at all, the idle went from perfectly normal to doing exactly what you are explaining. First it went to over 3000rpm so I took it out again and cleaned it a second time and it would idle to 1800rpm and wouldn't budge at all until I held the clutch for a sec or two. Replaced iac and back to normal. When I had the live data going it always showed the iac open like 40% or something I believe when it was happening.

 

[410Fortune]

suspect leak in your intake between MAS and throttle body, check the intake air hose VERY WELL for air leaks, the old intake hoses like to crack in the seems of the accordion portion

Any check engine light?

A 92 PCM is getting older, I have seen some idle issues like this especially on the 5 speed trucks, that ended up being a faulty PCM due to age/wear/use
After trying everything, new MAS, new IAC, new intake gaskets, in more then one instance it was a bad PCM

First for you though I would suspect the basics
Leaky intake tube
Faulty/ dirty IAC
Faulty TPS
Faulty or dirty MAS
Leaky intake plenum gaskets
Leaky lower intake gasket

 

[Dragone#19]

This reminds me a little bit of a Mass Airflow Sensor problem, but the change with using the clutch is a odd. I might look at that, clean it, measure voltages. Not definitive, but it's easy, and it's never a bad idea to clean an MAF... fast and easy.

As mentioned, this is an easy check. Disconnect your battery ground, remove and clean your MAF sensor. Reassemble. Allow your engine to run for about 5 minutes so that the pcm can relearn. This is similar to when you upgrade your air intake system to a K&N.

 

[Centaurious]

There is a vacuum hose that runs the cruise control, pinch that off to see if the unit is leaking.

 

[acschilling]

Did you get this figured out?!? I'm having an idle issue too. My 92 5 speed had a wicked high idle, like it would hang at 2000 and slowly dropped as it warmed up. Changed the coolant temp sensor, thermostat and fuel filter and now it'll randomly idle at 1500. Sometimes it's normal, sometimes it'll get that cruise control feeling and idle high when I'm stopped. Seems more of a cold weather occurring phenomenon now. If I stop and shut it off then restart it'll idle done around 1000. And the speedometer just went crazy yesterday. Jumps everywhere, and will say I'm doing 75 when it's maybe 45 or 50 I'm actually doing.