RPM dips/engine stalls at idle (intermittent), 99 4.0
- Thread starter Mercury
- Start date
Replaced the throttle body today, confirmed with a smoke tester that there were no leaks. When I started it, it ran great, no miss. Then slowly the miss came back, then the idle got rough, then it started trying to die, and when I ran my scanner I have both upstream and downstream O2 high voltage codes and upstream heater circuit fail.
I used the same sensors, just replaced the TB itself.
JPNinPA
Well-known member
Changing TB and moving some TB sensors do not cause O2 codes specifically voltage hi readings.
This sounds like a wiring grounding issue. This us good to check anyway. Check battery health. Inspect snd polish terminals and connector surfaces. Inspect wires for corrosion. Go to the opposite side of thev grounds snd disconnect, inspect and polish to shiny metal the bolt, connector and body, frame or frame area. There should be 2 main grounds. One to the engine and one to the body. Then clean the power sides.
Every 2-3 years its worth inspecting and cleaning grounds.
Id also wiggle wires and connectors while idling to check for bad contact broken wires.
Never look down on anyone unless you are helping them up - Jesse Jackson
It really makes no sense that it would make a difference. I even noticed on the new TB that the IAC sat a little loose, so I replaced the o-ring and no change. Stopped and started the Jeep multiple times and it ran terribly. Then as soon as I put the old one back in it started to run more normally.
I have no issue doing another check, but all of my ground cables have been maintained within the last 12 months. I replaced a few ground cables with thicker, 1/0 cable, and others I cut the lugs until I cleared any corrosion and crimped on a new copper lug. I even tracked down every thin wire ground and either replaced or crimped on a new terminal. Cleaned mating surfaces, etc. I had hoped there was a ground dedicated to the O2 sensors but it appears to ground through the PCM somehow, but since the PCM doesn't have its own ground, either, I'm not sure what else to check.
Exactly. But even sealing it all up, confirmed with the smoke test, the Jeep barely ran. Put the old one back on, it's back to where it was.
JPNinPA
Well-known member
If messing with or changing the TB gave a temp fix. Maybe the issue is there. Did you take any pics when you were cleaning your throttle body and IAC?
I don’t know how you cleaned throttlebody and IAC, but there is a method and sometimes if you don’t do it right, you could damage the IAC. Or you could have left some contaminants either on the IAC or where it sits, that would cause it to act erratically occasionally.
Do you have a gasket between your throttlebody and your intake Plenum?
While idling, have you taken anything like WD-40 or throttlebody cleaner and sprayed it around the base of the throttle body or the intake and exhaust area to see if the idle changes? This is useful for finding vacuum leaks.
Never look down on anyone unless you are helping them up - Jesse Jackson
I don’t know how you cleaned throttlebody and IAC, but there is a method and sometimes if you don’t do it right, you could damage the IAC. Or you could have left some contaminants either on the IAC or where it sits, that would cause it to act erratically occasionally.
Do you have a gasket between your throttlebody and your intake Plenum?
While idling, have you taken anything like WD-40 or throttlebody cleaner and sprayed it around the base of the throttle body or the intake and exhaust area to see if the idle changes? This is useful for finding vacuum leaks.
Never look down on anyone unless you are helping them up - Jesse Jackson
I changed the TB entirely a few days ago, unfortunately no change to the miss.
I swapped the IAC with an off brand, no change so I swapped it back.
When I cleaned the TB I followed a post of Jerry Bransford; ran the Jeep and sprayed directly in the TB, let it get close to stalling a few times, then stalled it and restarted a few times. I did the same thing recently with Seafoam intake cleaner, though twenty minutes after using it I drove it hard for twenty minutes.
Yes to the gasket, and I replaced it again a few days ago.
Outside of fuel injectors I'm not sure where else to look, or if I just need to start throwing sensors at it.
JPNinPA
Well-known member
No that is not how you clean the TB and IAC.
Give mea few to find the post,
https://www.jeepforum.com/threads/cleaning-iac-and-throttle-body-write-up-for-dummies.1114849/
And Jerry oversteps here with edits. Its true technically you don’t have to remove it. I do suggest removing the TB to clean. Not everyone can get in to verify it’s clean. Bringing it out into proper light like the images allows you to see the carbon is gone.
Also you described the new TB as having a loose IAC or not fitting…
Where did you get the new TB?
I bought Hesco. Works great.
Never look down on anyone unless you are helping them up - Jesse Jackson
Give mea few to find the post,
https://www.jeepforum.com/threads/cleaning-iac-and-throttle-body-write-up-for-dummies.1114849/
And Jerry oversteps here with edits. Its true technically you don’t have to remove it. I do suggest removing the TB to clean. Not everyone can get in to verify it’s clean. Bringing it out into proper light like the images allows you to see the carbon is gone.
Also you described the new TB as having a loose IAC or not fitting…
Where did you get the new TB?
I bought Hesco. Works great.
Never look down on anyone unless you are helping them up - Jesse Jackson
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Sorry, ended up in the hospital, took some of the steam out of my repairs.
I replaced the throttle body again, this time replacing the TPS as well, now it's running normally other than the miss.
I had my fuel injectors cleaned on one of those injector rigs. They all sprayed well, just a little build up, didn't fix the miss. Only odd thing: one of the injectors had a slightly higher output. At 40 seconds of high-level spray all of the injectors but one were at 80 ml, the oddball was at 86. That injector has a sticker on it that the others do not (though it's identical otherwise), so I wonder if that was a replacement.
Could that be enough to cause a small miss?
I replaced the throttle body again, this time replacing the TPS as well, now it's running normally other than the miss.
I had my fuel injectors cleaned on one of those injector rigs. They all sprayed well, just a little build up, didn't fix the miss. Only odd thing: one of the injectors had a slightly higher output. At 40 seconds of high-level spray all of the injectors but one were at 80 ml, the oddball was at 86. That injector has a sticker on it that the others do not (though it's identical otherwise), so I wonder if that was a replacement.
Could that be enough to cause a small miss?
Bummer. Hoping for an easy fix.
I'm thinking there's got to be an electrical issue somewhere. At this point I'm tempted to get a oscilloscope and check every circuit in the thing.
I may go have the compression checked again, maybe the first mechanic botched it.
Thank you! Have some tests at the hospital tomorrow, fingers crossed.
JPNinPA
Well-known member
The only other things i could think of and only if it tracks timing. Check odpa or distributor gear to CAM gear for wear. 2003-2006 ODPA did not self lube properly causing gear wear and eventually miss or screaming monkies.
Second worn CAM lobes or bad lifter.
Though these should cause a misfire code. Even in the early stages.
So I doubt but worth looking at if you have the time snd it bothers you that much.
Never look down on anyone unless you are helping them up - Jesse Jackson
Second worn CAM lobes or bad lifter.
Though these should cause a misfire code. Even in the early stages.
So I doubt but worth looking at if you have the time snd it bothers you that much.
Never look down on anyone unless you are helping them up - Jesse Jackson
I'm considering pulling the head and taking it to a machine shop. I'm still driving it, it's behaving well otherwise, but I want to fix this before it leads to other problems.
Hmmm. I'll look into those, I'm really just out of ideas other than maybe a tiny amount of coolant is leaking through the gasket.
