Rough idle, no codes.
11-04-2014, 12:19 AM
#1
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Year: 1999
Model: Cherokee
Engine: 4.0 I6
Rough idle, no codes.
I've checked the other rough idle threads. Everybody has a different setup or different symptoms. Today I got an obd2 scanner. One of the ones that you can connect with the wifi signal to a third party app on your iPhone. I just want to know what's up with the idle on my xj. So far I've done the 784 injector swap, new plugs, wires, dizzy, rotor, and new air filter, I even started running better fuel. It doesn't really feel like it is missing, and it isn't consistent, but the jeep vibrates a hair when the rpm dips. It is only at idle, and while playing with my new scanner I found that if I slightly give it throttle the vibrations go away and the rpms evened out. I'm talking about just the slightest amount of throttle, still below 800 rpms. Somedays the symptoms are worse than others but there has never been a common condition that would cause the problem. The only thing I can think of is the xj's heat soak issues. I still have this problem no matter what the temperature is outside. Recently I opened the hood and let it idle while at operating temp to see if it helped. It seemed like it did a little, but the problem still seemed underlying. I should've threw a box fan on top of the fuel rail to further troubleshoot but I didn't have time and I figured that it was cool enough out that it wouldn't matter if I had the fan. What do you guys think? Should I play with my idle, explore more into the heat soak, or try a different route?
Here is a screen shot of my xj idling for 30 seconds at running temp. It bounced around between 710 and 740.
Here is a screen shot of my xj idling for 30 seconds at running temp. It bounced around between 710 and 740.
11-04-2014, 02:08 AM
#2
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Year: 1999
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I should mention, the problem also occurs when it is at a slightly higher idle during warm-up. Unless I apply the throttle slightly.
11-04-2014, 06:39 AM
#4
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Ever clean the throttle body and IAC?
Courtesy of TJWalker:
--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.
CLEANING THE JEEP 4.0 IDLE AIR CONTROL
Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On 91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
“Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner
It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled
Revised 10-6-2014
Courtesy of TJWalker:
--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.
CLEANING THE JEEP 4.0 IDLE AIR CONTROL
Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On 91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
“Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner
It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled
Revised 10-6-2014
11-04-2014, 06:22 PM
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11-04-2014, 06:32 PM
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Ever clean the throttle body and IAC? Courtesy of TJWalker: -------------------------------------------------------------------- The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present. CLEANING THE JEEP 4.0 IDLE AIR CONTROL Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On 91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled Revised 10-6-2014
As far as the iac goes I'll check it out. I might just replace it.
My last dd was an 01 Mercury cougar v6 pos. I cleaned the throttle body and iac on it. Talk about nasty!! I was scraping crap off with a screw driver before I hit it with the cleaner. It also had vacuum problems and a bad iac. Cleaning the iac only solved the problem for a day. I ended up buying a new one.
11-04-2014, 06:39 PM
#7
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Year: 1990
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I know the throttle body is clean, I've had it off a few times, and I've never cleaned it. It has always been shiny and clean.
As far as the iac goes I'll check it out. I might just replace it.
My last dd was an 01 Mercury cougar v6 pos. I cleaned the throttle body and iac on it. Talk about nasty!! I was scraping crap off with a screw driver before I hit it with the cleaner. It also had vacuum problems and a bad iac. Cleaning the iac only solved the problem for a day. I ended up buying a new one.
As far as the iac goes I'll check it out. I might just replace it.
My last dd was an 01 Mercury cougar v6 pos. I cleaned the throttle body and iac on it. Talk about nasty!! I was scraping crap off with a screw driver before I hit it with the cleaner. It also had vacuum problems and a bad iac. Cleaning the iac only solved the problem for a day. I ended up buying a new one.
Do as you choose.
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11-04-2014, 08:13 PM
#8
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Year: 1999
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It could be a fuel pump starting to show issues. Have you checked all of the electrical connections by the coil and distributor? I have been having an issue with mine, getting sluggish and missing. I am sure my fuel pump is on it's last leg.
11-05-2014, 12:41 AM
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All connections are good, the coil could possibly be going bad. Typical xj problem. I had to replace my cps recently too. As far as the fuel pump goes, it's quiet, and I have good fuel pressure.
11-05-2014, 12:55 AM
#10
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For all I know it was cleaned right before I bought it, I've only put maybe 15k on the engine since then.
I was just saying that I know it is clean, and have been lucky enough to not have needed to clean it yet.
11-06-2014, 01:05 AM
#11
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I've confirmed a cracked header. If it's not the cause of the rough idle, it can't be making the problem any better.
11-12-2014, 04:28 PM
#12
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I pulled and cleaned the throttle body and iac today. The jeep is on stands cause I'm also in the middle of doing shaft and pinion seals in the front. I'll let you guys know how it runs in a bit. Hopefully. Here's the pic I promised of the tb. The dirtiest I've seen it, but in all, it wasn't bad. It cleaned right up.
11-14-2014, 01:54 PM
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I'm still having issues, though they may have improved just a hair. I really need to get a new header and see if that helps.
11-28-2014, 06:47 PM
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I'm still having the issue, my next plan of action is to replace my header. It needs it anyway. Then I'll replace the ignition coil. I don't have much to update until I've got some extra money.