I've been having some idling issues on my 94 4.0 YJ for a while now, and frankly I am tired of them. When I crank the Jeep up, it usually idles a little rough. Nothing terrible, but it vibrates the Jeep a bit and you can definitely feel it. My RPM is usually 1500 when it first starts up, then it drops to 800 for a few seconds, and then 500-600ish.
As it warms up, the idle is just slightly choppy. It kind of sounds like it's hiccuping. If I want to drive, I can and it'll drive perfectly fine.
Now, about my idle RPM. If I've been sitting for a minute or so and I back out of say a parking spot in reverse..when I come to a stop to put it in first gear to start moving forward, as I come to a stop in reverse, the rpm will sometimes drop to 200 or so when I push the clutch in and am shifting from reverse to first. It does not do this every time, but I have definitely seen this more times than I can count on my hand.
Another instance is when I'm cruising down the road, I have to come to a stop, and I push the clutch in and go to neutral. Initially the idle goes to around 700-800 RPM, and then as I slow down it'll drop more. Sometimes it'll drop to 300, sometimes 500, sometimes 500 and then when I'm fully stopped, 300. There's really no predicting. When it's bogging way down at 300, it feels like it's about to stall. It has never stalled, and I've been having this problem since November.
So, these are the things I have done so far to fix this, and have so far pretty much all been failed attempts. The problem still persists fully.
My OEM Vehicle Speed Sensor was leaking at the electrical plug. It had ATF from the transfer case inside the electrical connector. I cleaned this with electronic cleaner a few days ago. My connector is dirty again, but I'm not sure how quickly that happened so I didn't really have a long enough time to get good results from the cleanse. I have a buddy with a 97 TJ (same speed sensor as the YJ) that I'm going to borrow from and see if that makes any difference. I'm hopeful but not optimistic.
I am on a new tune-up. I have Autolite Iridium XP spark plugs, Mopar ignition wires, Mopar cap, Mopar rotor, and Mopar ignition coil. A few weeks ago I installed this tune-up as a replacement for my previous Firepower DUI Ignition kit with a Screamin' Demon coil, which had the plugs gapped at .065". This idle problem has existed since before either of these tune-ups were installed. Neither installation made a difference at all.
I have a 6 month old NTK O2 sensor. NTK is the OEM brand, so I feel that it should be working fine. Could be faulty of course, I don't know.
I have messed with the IAC more than enough times and it has produced no results. First, I cleaned my OEM IAC and throttle body with throttle body cleaner. That made no difference. Next, I replaced my OEM IAC with a BWD IAC from O'Reilly. Also made no difference. Thinking maybe I got a faulty sensor from O'Reilly (which happens pretty frequently), I scavenged out a Mopar IAC. Still, no difference.
I have a new BWD TPS from O'Reilly. I am skeptical of it, but I tested it and the voltage range seems smooth so I feel that my problem doesn't lie here. The voltage goes from lower than my tester can count at idle to 3.80 volts at Wide Open Throttle. The FSM states that it needs to be below 4.80 at WOT, so I'm not too worried about that. The smooth voltage range across the accelerator makes me think it's fine.
When I was doing my coolant system flush and 195º thermostat a few weeks ago, I installed an Echlin brand coolant temp sensor in the thermostat housing. Being that it's a parts store brand part, I am a little skeptical of it as well, but I notice 0 behavior differences after installation so I'm thinking it must be fine.
I have a new battery, which is working fine daily.
I have a new non-cracked exhaust manifold.
I have 0 vacuum leaks. Vacuum leaks give high idle rather than low anyways, but just feel the need to mention it since usually somebody says check vacuum.
I have reset the computer into adaptive learning mode several times, with the same results each time. Nothing has fixed my problem yet.
So, what am I up against? The only things I can think of are:
-The speed sensor just gets dirty with ATF too quickly to be able to get a good reading to ever behave correctly before it gets dirty and starts giving bad readings again. I am iffy on this since my speedometer works perfect and always has. Testing my friend's speed sensor will hopefully clear some of my curiosity.
-The TPS from O'Reilly is bad even though it seems okay by test
-The MAP sensor is faulty. I've tested it and I think it's okay but I'm not too sure.
-Maybe (unlikely) the Coolant temp sensor is faulty, but I really doubt it.
-I might need a new intake air temp sensor, haven't really looked into the likelihood of that much.
-and Lastly, maybe I need another O2 sensor from NTK.
My guess is the computer doesn't just "forget" how to run right, does it? I mean, 3 years ago this wasn't a problem at all when I bought it and over time this idle issue became worse. I figure surely it's a sensor problem and not the computer needing replacement. I sure hope so anyways.
So, I am VERY tired of troubleshooting this and throwing parts at it, and want this fixed. If any of you have any ideas, please post them up. Thanks. I want my properly running Jeep back.
As it warms up, the idle is just slightly choppy. It kind of sounds like it's hiccuping. If I want to drive, I can and it'll drive perfectly fine.
Now, about my idle RPM. If I've been sitting for a minute or so and I back out of say a parking spot in reverse..when I come to a stop to put it in first gear to start moving forward, as I come to a stop in reverse, the rpm will sometimes drop to 200 or so when I push the clutch in and am shifting from reverse to first. It does not do this every time, but I have definitely seen this more times than I can count on my hand.
Another instance is when I'm cruising down the road, I have to come to a stop, and I push the clutch in and go to neutral. Initially the idle goes to around 700-800 RPM, and then as I slow down it'll drop more. Sometimes it'll drop to 300, sometimes 500, sometimes 500 and then when I'm fully stopped, 300. There's really no predicting. When it's bogging way down at 300, it feels like it's about to stall. It has never stalled, and I've been having this problem since November.
So, these are the things I have done so far to fix this, and have so far pretty much all been failed attempts. The problem still persists fully.
My OEM Vehicle Speed Sensor was leaking at the electrical plug. It had ATF from the transfer case inside the electrical connector. I cleaned this with electronic cleaner a few days ago. My connector is dirty again, but I'm not sure how quickly that happened so I didn't really have a long enough time to get good results from the cleanse. I have a buddy with a 97 TJ (same speed sensor as the YJ) that I'm going to borrow from and see if that makes any difference. I'm hopeful but not optimistic.
I am on a new tune-up. I have Autolite Iridium XP spark plugs, Mopar ignition wires, Mopar cap, Mopar rotor, and Mopar ignition coil. A few weeks ago I installed this tune-up as a replacement for my previous Firepower DUI Ignition kit with a Screamin' Demon coil, which had the plugs gapped at .065". This idle problem has existed since before either of these tune-ups were installed. Neither installation made a difference at all.
I have a 6 month old NTK O2 sensor. NTK is the OEM brand, so I feel that it should be working fine. Could be faulty of course, I don't know.
I have messed with the IAC more than enough times and it has produced no results. First, I cleaned my OEM IAC and throttle body with throttle body cleaner. That made no difference. Next, I replaced my OEM IAC with a BWD IAC from O'Reilly. Also made no difference. Thinking maybe I got a faulty sensor from O'Reilly (which happens pretty frequently), I scavenged out a Mopar IAC. Still, no difference.
I have a new BWD TPS from O'Reilly. I am skeptical of it, but I tested it and the voltage range seems smooth so I feel that my problem doesn't lie here. The voltage goes from lower than my tester can count at idle to 3.80 volts at Wide Open Throttle. The FSM states that it needs to be below 4.80 at WOT, so I'm not too worried about that. The smooth voltage range across the accelerator makes me think it's fine.
When I was doing my coolant system flush and 195º thermostat a few weeks ago, I installed an Echlin brand coolant temp sensor in the thermostat housing. Being that it's a parts store brand part, I am a little skeptical of it as well, but I notice 0 behavior differences after installation so I'm thinking it must be fine.
I have a new battery, which is working fine daily.
I have a new non-cracked exhaust manifold.
I have 0 vacuum leaks. Vacuum leaks give high idle rather than low anyways, but just feel the need to mention it since usually somebody says check vacuum.
I have reset the computer into adaptive learning mode several times, with the same results each time. Nothing has fixed my problem yet.
So, what am I up against? The only things I can think of are:
-The speed sensor just gets dirty with ATF too quickly to be able to get a good reading to ever behave correctly before it gets dirty and starts giving bad readings again. I am iffy on this since my speedometer works perfect and always has. Testing my friend's speed sensor will hopefully clear some of my curiosity.
-The TPS from O'Reilly is bad even though it seems okay by test
-The MAP sensor is faulty. I've tested it and I think it's okay but I'm not too sure.
-Maybe (unlikely) the Coolant temp sensor is faulty, but I really doubt it.
-I might need a new intake air temp sensor, haven't really looked into the likelihood of that much.
-and Lastly, maybe I need another O2 sensor from NTK.
My guess is the computer doesn't just "forget" how to run right, does it? I mean, 3 years ago this wasn't a problem at all when I bought it and over time this idle issue became worse. I figure surely it's a sensor problem and not the computer needing replacement. I sure hope so anyways.
So, I am VERY tired of troubleshooting this and throwing parts at it, and want this fixed. If any of you have any ideas, please post them up. Thanks. I want my properly running Jeep back.
