Unique high RPM at idle

jwilkinson01

jwilkinson01

TJ Enthusiast
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Supporting Member
Joined
Dec 16, 2016
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348
Location
Aurora, CO
I have tried everything I can think of at this point, I need help from the experts. The symptoms are idle starts out about 1100 then after about a minute it quickly climbs to about 2300.

History: swapped in a low mileage 4.0, drove it for a couple days with no idle issues. Had an exhaust leak from the manifold gasket. I had been collecting parts I was planning on throwing on my stroker build, figured since I was pulling it all apart to get to the gasket I might as well throw them on instead of letting them sit for 2 more years. So installed Edlebrock head, Clifford headers with custom down pipes new muffler and new nkt O2s, sheet metal intake manifold, oversized TB, windstar intake. I relocated the evap system and cruise control module due to genright fender install.

What I have done: did a smoke test on the vacuum system and I am not seeing anything. I had a NIB mopar IAC so I put that in. Throttle cables seem to move freely. No codes.

Thanks
 
Been doing a lot of reading since it’s too dark out to keep screwing with anything. Obviously something I did caused the problem.

I have no idea if it could be related but I also removed the AC compressor, lines and under hood components.

I also removed all the ABS junk.
 
What about the reservoir on the passenger fender? Did that get removed for the genright fenders? It would T off the HVAC fitting beside the ECU and drop down out of site. I also assume you still have your one way valve for that line?

IMG20240817145059.jpg


-Mac
 
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I am wondering if I had the exhaust shop use the right O2 sensors. I bought the NGK sensors ages ago based on the official O2 sensor thread but it looks like the part numbers listed for the 2000 with only 2 sensors has been updated sometime since I bought the ones I had which are the 2 listed for a 99
 
Last edited:
Zorba said:
Check the CCV system, and make sure you have the correct elbow with the little orifice in the rear of the valve cover.
Click to expand...

I replaced both the front and back so they “should” be correct. Is there a way to verify without pulling the valve cover (again)?
 
jwilkinson01 said:
I am wondering if I had the exhaust shop use the right O2 sensors. I bought the NGK sensors ages ago based on the official O2 sensor thread but it looks like the part numbers listed for the 2000 with only 2 sensors has been updated sometime since I bought the ones I had which are the 3 listed for a 99
Click to expand...

That's because NTK no longer makes them.

They came up with a universal part that's basically with a longer wire or something...instead of two identical parts one with 6 inches more of wire.

What voltages are showing for the O2s in ODB live data? Anything below.9v generally and simplistically saying is a significant a good O2 sensor.

Also...the PCM doesn't change idle based on O2s.

It's either vacuum or your IAC...and since you don't have a stock TB perhaps that's the issue?

-Mac
 
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macleanflood said:
That's because NTK no longer makes them.

They came up with a universal part that's basically with a longer wire or something...instead of two identical parts one with 6 inches more of wire.

What voltages are showing for the O2s in ODB live data? Anything below.9v generally and simplistically saying is a significant a good O2 sensor.

Also...the PCM doesn't change idle based on O2s.

It's either vacuum or your IAC...and since you don't have a stock TB perhaps that's the issue?

-Mac
Click to expand...

I can put the old TB back on and see if that changes anything. IAC is brand new Mopar. TPS and MAP are original that I swapped over to the new TB.
 
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Last week I had a high idle issue after having a dead battery from leaving the dome light on over night. I charged the battery, and drove around as usual for a day and everything was normal. On day two I noticed the idle speed was above 1100rpms, I was thinking a vacuum leak or IAC but for kicks I disconnected the battery for 30 minuets with both cables touching. After 30 minuets I hooked everything back up and the idle returned to normal. Easy fixes don't usually happen for me but that day the stars aligned. :)
 
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jwilkinson01 said:
I replaced both the front and back so they “should” be correct. Is there a way to verify without pulling the valve cover (again)?
Click to expand...

If you just replaced them - its likely your smoking gun as many/most parts lists are wrong and you end up with the wrong part (ask me how I know this). Pull the rear elbow, no need to remove the VC, and make sure it has the restrictor in it. If it doesn't, check the front one for the unlikely event that they got reversed. You need the elbow the restrictor in the rear position...
 
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jwilkinson01 said:
I have tried everything I can think of at this point, I need help from the experts. The symptoms are idle starts out about 1100 then after about a minute it quickly climbs to about 2300.

History: swapped in a low mileage 4.0, drove it for a couple days with no idle issues. Had an exhaust leak from the manifold gasket. I had been collecting parts I was planning on throwing on my stroker build, figured since I was pulling it all apart to get to the gasket I might as well throw them on instead of letting them sit for 2 more years. So installed Edlebrock head, Clifford headers with custom down pipes new muffler and new nkt O2s, sheet metal intake manifold, oversized TB, windstar intake. I relocated the evap system and cruise control module due to genright fender install.

What I have done: did a smoke test on the vacuum system and I am not seeing anything. I had a NIB mopar IAC so I put that in. Throttle cables seem to move freely. No codes.

Thanks
Click to expand...

Have you replaced your ICA ( Idle Control Valve)?
 
Old Jeepin Cowboy said:
WOW! Any chance it may be faulty??? Or an intermittent connection. My TJR did it but a simple tap on the go pedal and it went away, but it did not do it constantly.
Click to expand...

I don’t think so. I don’t think the first one was faulty. But I replaced it because the IAC seems to be a common problem. It was a brand new in the box Mopar.
 
Zorba said:
If you just replaced them - its likely your smoking gun as many/most parts lists are wrong and you end up with the wrong part (ask me how I know this). Pull the rear elbow, no need to remove the VC, and make sure it has the restrictor in it. If it doesn't, check the front one for the unlikely event that they got reversed. You need the elbow the restrictor in the rear position...
Click to expand...

The elbow in the back is gray, and it has the part number 53030495 Stamped on it. From what I’ve read that’s the correct for the rear.
 
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