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Discussion Starter · #1 ·
I know this issue has been talked about many times. I have read everything I can find about it. I have looked and looked again for vacuum leaks and replaced all kinds of gaskets and hoses. I honestly dont think it is a vacuum leak now. What else can cause this high idle. What sensors can cause it?
 

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OK it's a 99 but what motor??? TBI or EFI or Carb???

Let us know. It makes a difference and I can't see much on the phone.
 

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OK that is my setup.

Most common is an intake and exhaust manifold leak, cracked vacuum lines or one missing.

Since you have a throttle body you have an ISA and TPS and WOT.

TPS Throttle position Sensor tells the ECU throttle position.

WOT Wide Open Throttle Switch lets ECU know when throttle is wide open

ISA I believe Idle Solenoid Assembly It sets the idle according to ECU commands but it has ops check and adjustment.

You have a MAP sensor on the firewall with a vacuum line running to it.

Temp sensors on the intake and the cylinder head. One on the cylinder heads runs the gauge the one on the intake talks to ECU which when warmed up comes out of closed loop and drops your idle. It is the IAT Inlet Air Temp Sensor.

O2 sensor on the exhaust tells ECU how it is running and adjust mixture which may have some bearing on idle but usually fuel mixture

You have an EGR solenoid which can be checked by opening the throttle and it should open as it decelerates. You can get a finger on it and rap the throttle and when you let go it should move.

CPS crank Position Sensor on the bell housing at 10 O'clock tells ECU crank position using a transducer used to set timing.

Timing on the 2.5L is set by ECU at 8 degrees BTDC.

So that is what I know about the sensors. I have a couple of pics one of the vacuum system and some charts for resistance checks on the IAT

What would I check first would be the timing.

Check wiring connections to all sensors and clean and use some dielectric grease on them plug them back together.

Just for shits and grins what thermostat you run. OE is 195 and if thats what you have leave it alone unless your gauge says you are running cold (closed loop) no ECU.

When you start up it takes a few seconds for the ECU to bring the idle down from about 1800 on mine and then it stays up above 750 RPM until warm and then will settle at pure idle. That is why I say temp sensor.

Best I got I know I spammed you with a lot of random thoughts but should give you some good stuff to check without replacing everything.
 

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OK that's great.

I would go check all electrical connections first. Clean if needed.

Then I would check the function of sensors related to temp which are on the intake one for air temp one for water temp. They signal the ECU and when it is warmed up the idle should fall to normal.

Even cold you can throw a timing light on it and see if your timing is setting correctly. The ECU sets timing from inputs.
 

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Discussion Starter · #7 ·
Ok thanks for all the info Chief.I will have to check all this stuff and maybe I will be able to get this issue resolved. I am not very mechanically inclined as this I'd the first vehicle I have owned that I am doing the repair work on.
 

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Discussion Starter · #8 ·
I forgot to mention that I took it up to the mountains and when it was up in the higher altitude the idle dropped back down to normal. I don't know if that will help narrow it down but I thought I should mention it.
 

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Discussion Starter · #10 ·
Ok so I cleaned and greased all the connections like suggested and what do you know? It helped a lot. Dropped the idle down about 1000 rpm. The only thing is that the idle rom is fluctuating. It will rise to about 1400 then come back down and keep doing that. Any suggestions on what could cause that.
 

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all of you are going to hate me but can someone please tell me how to post a thread? I'm a new member to WF although i have read for over a year now. sorry for the annoying question but any help would be appreciated! thanks!
 

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unplug the sensor on the power steering line... thats what fixed mine.
 

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mines doing the same was told to try and replace the iac so I did and it helped for a little bit but now I'm back to high idle around 2000 but the other day while driving it jumped to 3000. Today I was messing with it and had it unplugged and not thinking I started it to move back a bit, dropped a screw, and it started fine wondering if I may have a bad iac valve and the computer is compensating for it.
 

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Discussion Starter · #15 ·
image-2058904544.jpg
Happy day. It seems to be fixed. I removed the idle speed motor and cleaned it thoroughly and installed it back in and it seems to be holding. I have been letting it idle for about 10 minutes and it hasn't gone up. Time to take it for a drive.
 

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Discussion Starter · #16 ·
Ok so it is back up to 1500 now. If cleaning it temporarily fixed it would getting a new one fix it for good? Or is there a calibration or reset I should do?
 
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