94' High Idle problem

[Rooster]

I have searched and researched this issue and can not find a similiar issue.

Going home from work, car started fine and drove fine for about 10 miles (no previous symptoms or fault indications), stopped for a red light and noticed I had to apply a little more than normal brake pressure and that the engine was suddenly idling high.

Got home, put it in park and the idle jumped to about 2500. Shut the car off, waited a few minutes and restarted, still running high, though at about 1500 rpms. No CEL indication.

I checked all the vacuum lines visually and used carb cleaner, even sprayed around the manifold. I cleaned the TB, MAF, and IACV - no joy. I changed the TPS and IACV - disconnected the neg on battery for 30 min. Restarted the car and the idle went down to 1000 rpm. Stopped to stratch my head and continue research.

Next morning, started car, idle normal, drove fine for about 10 miles and noticed the idle was high again. When I got back home it was idling (park) about 1200 rpm. I read something about the heat indicator to PCM affecting RPM, so I turned the heater on full and the RPM dropped down to about normal. Shut off heater and RPM shot back up?

I am getting a litle leary of chasing parts, anyone here experience the same symptoms or could shed some insight to troubleshooting this further.

Thank you in advance.

 

[LXNavajo_94]

It seems to me that there are 2 coolant temp sensors on a 94 and 1 just goes to the gauge the other goes to the pcm. They are both located near the thermostat housiing. if the one feeding the pcm goes bad this could be your problem. I would check the wiring first. You might want to pull codes using the paperclip method just to see if you do have a code even though the CEL isn't on if you haven't already done so. This might help diagnose whats ailing it.

 

[Rooster]

LX Navajo, Thank you for the quick reply. Could you please explain the paper clip method?

 

[LXNavajo_94]

Rooster the paper clip method is actually a sticky on this forum heres the link http://www.explorerforum.com/forums/showthread.php?t=255962
That should explain it alot better than I can here. If you find the codes and post em here I'm sure we can start to narrow down this problem. Also sorry I'm just now getting back to you I work in HVAC and we had some rather snowy weather here today and I have been running service calls like a madman

 

[Rooster]

Update to idle problem: It was a bit chilly this morning so I used the heater to defrost the windows. After car came to temp the idle started to ride high - with my foot off the gas, the car would drive itself at 45mph.

In park the idle stayed at 2500; tried to fast rev to get it to come down, did work. This is really making my head hurt.

Navajo, thank you for the link.

 

[Rooster]

Just a quick update for those who may come across the same issue.

I replaced the coolant temperature sensor and sender units. I replaced the sender unit for the gauge that has not risen off the left side for a number of years.

When I replaced the sensor unit, my high idle stabilized from idle to exceration. My idle in park is now around 950 and 650-700 in gear. So, this now leads me to think I have a thermostat issue. Either it is open or partially open - not allowing the car to warm up properly.

The gauge is still not reading right? Not an issue right now. Perhaps the thermostat will fix this as well?

 

[LXNavajo_94]

sounds to me like your on the right track with the sensor replacement. I'm thinking the t -stat will be the final step to correct it. Your welcome for the link it has saved me countless hours of chasing issues.