Idle speed and adjustment
- Thread starter grrnmo
- Start date
Both of mine Idle about 550-600. My 94 grand will sometimes stumble when it is first started when cold but then evens out smooth within a few seconds. If you have not done a tune up in while now would be a good time to eliminate the possibility of a ignition problem such as a plug or plug wire. It really shouldn't idle that rough, and if it does it may be a good indication there is a problem somewhere else that needs to be addressed. I am not sure about the idle adjustment produres I have not had to use them but I am sure there in whatever service manual have. If you dont have a manual let me know and I will look at mine and post the info.
Bounty__Hunter
Super Moderator
No idle adjustment on your ZJ, it's all computer controlled. Look for the source of the rough idle, possibly the IAC motor or TPS. Does it trip the 'check engine' light?
Hi,
Mine idles around 600-700 RPMs.
You CANNOT adjust the idle speed on computer controlled vehicles (which is all cherokees), since the idle is a preset function of the computer. The idle is controlled by the Idle Air Control motor (IAC) and if it gets dirty it can cause irratic idle. Clean the Throttle Body and IAC air channels. Sensors which affect the idle through the computer are the Throttle Position Sensor (TPS), Coolant Temp. Sensor (CTS), Manifold Absolute Pressure Sensor (MAP), and the Oxygen sensor (02) which is only included while the engine is at normal operating temperature. :mrgreen:
Do you have an automatic transmission?
-Nick :!:
Mine idles around 600-700 RPMs.
You CANNOT adjust the idle speed on computer controlled vehicles (which is all cherokees), since the idle is a preset function of the computer. The idle is controlled by the Idle Air Control motor (IAC) and if it gets dirty it can cause irratic idle. Clean the Throttle Body and IAC air channels. Sensors which affect the idle through the computer are the Throttle Position Sensor (TPS), Coolant Temp. Sensor (CTS), Manifold Absolute Pressure Sensor (MAP), and the Oxygen sensor (02) which is only included while the engine is at normal operating temperature. :mrgreen:
Do you have an automatic transmission?
-Nick :!:
I was going to look at the manual after I posted just to see how it is done to satisfy my own curiousity but I got sidetracked. I had just assumed that there was some sort of adjustment I guess I would have had a similiar results though. But as they say assumption is the mother of all ****ups. Thank you bounty-hunter and xjnick for info, it will save me the trip to the manual. Sorry to grrnmo if you read your manual yet probably again and still found no adjustment. 
Howdy all I'm having the same problem, I've already done the tune up replaced fuel filter, jeep came w/ brand new injectors, sending unit and tank. It ran great for a week after the tune up but now is doing same thing again. I cannot find the "Idle Air Control Motor" in the manual--possible it has another name? Also I was reading the manual and it was talking about the Ignition module, which is mounted directly under the ignition coil, any idea where I can get one?
YJ Windshield
Hi,
You didn't say what model year you own, but for the purpose of the reply i'm going to assume it's pre '97.
Anyways, the Idle air Control motor to my knowledge is called the IAC motor or such, if your looking in a haynes or chilton manual and it is not listed then that is no surprise to me as they are both seriously lacking in information about the electrical and computer systems.
The Idle air control motor is a cylindrical object bolted to the side of the throttle body which faces the front of the vehicle. It has an oval shaped 4-pin electrical plug. The motor can be cleaned, but not adjusted.
The ignition module on earlier cherokees is part of the ignition coil, i.e. they are a set and have to be purchased together. As you stated, they ARE on top of one another.
-Nick :!:
Hi,
You didn't say what model year you own, but for the purpose of the reply i'm going to assume it's pre '97.
Anyways, the Idle air Control motor to my knowledge is called the IAC motor or such, if your looking in a haynes or chilton manual and it is not listed then that is no surprise to me as they are both seriously lacking in information about the electrical and computer systems.
The Idle air control motor is a cylindrical object bolted to the side of the throttle body which faces the front of the vehicle. It has an oval shaped 4-pin electrical plug. The motor can be cleaned, but not adjusted.
The ignition module on earlier cherokees is part of the ignition coil, i.e. they are a set and have to be purchased together. As you stated, they ARE on top of one another.
-Nick :!:
Hi,
On the OBD-I Jeeps (pre '95), I'm fairly certain the answer is no. The OBD-I systems really weren't that complicated. The newer jeeps with OBD-II the answer would be yes.
Also, I forgot to mention above that you need to be sure you DO NOT move the IAC motor tip while you have the motor removed. It must remain in the same position or it can become damaged.
-Nick :!:
On the OBD-I Jeeps (pre '95), I'm fairly certain the answer is no. The OBD-I systems really weren't that complicated. The newer jeeps with OBD-II the answer would be yes.
Also, I forgot to mention above that you need to be sure you DO NOT move the IAC motor tip while you have the motor removed. It must remain in the same position or it can become damaged.
-Nick :!:
Bounty__Hunter
Super Moderator
I thought the IAC motor and housing were on the pass. side of the TB, with the throttle cables being the only thing on the front of the TB.
Bounty__Hunter said:
On the older Cherokees, both the IAC motor and the Throttle Position sensor (TPS) are on the side of the TB which faces the front of the Jeep (and which i'm calling the front of the TB). Nothing is on the passenger side of the TB except the vacuum line for the Manifold Absolute Pressure sensor (MAP), and the throttle cable comes to the rear (side facing the firewall) of the Throttle body.
-Nick :!:
-Nick :!:
grrnmo said:
I asked if it was auto or not, because with an Automatic Transmission the Torque converter can cause the Jeep to idle low if it is not functioning properly. I'd imagine it could likewise cause vibration if it is not releasing properly. But I'm not an expert with automatic transmissions - I only own vehicles with manual transmissions :mrgreen:
-Nick :!:
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