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JMO413

What does your MJ idle at?

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This is just a general question. I have read through quite a few threads on here and there is no real answer to this question. Not looking for any real answer just data to compare.

 

Mine idels at right about 750 according to the tach. That's what I believe the 2nd line on the tach is.

IMG_20191004_191957916.jpg.55635fcc9f7c8dd7bd5cf497a2f691fb.jpg

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My 91 idles at precisely that second line on the tach. Not sure what speed the computer is requesting, but I could hook up the MT2500 tomorrow if you wanted an exact number.

 

My 89? Wherever it feels like, thanks no doubt to a handful of vacuum leaks.

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AC ON or AC OFF, your idle speed should be the same. Your idle is high. My understanding is that 750 will be the target RPM's with engine at normal operating temperature.

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32 minutes ago, Minuit said:

My 91 idles at precisely that second line on the tach. Not sure what speed the computer is requesting, but I could hook up the MT2500 tomorrow if you wanted an exact number.

 

My 89? Wherever it feels like, thanks no doubt to a handful of vacuum leaks.

If you feel like it that I would definitely like to know what it says. If your going to my second question is whether or not it does your idle jumping around. Mine jumps between 715 and 750 almost constantly. I'm guessing this from the O2 sensor switching from lean to rich. They change at about the same rate on the scanner.

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3 minutes ago, Ωhm said:

My understanding is that 750 will be the target RPM's with engine at normal operating temperature.

This is truly the answer I have been looking for. 

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1 minute ago, JMO413 said:

If you feel like it that I would definitely like to know what it says. If your going to my second question is whether or not it does your idle jumping around. Mine jumps between 715 and 750 almost constantly. I'm guessing this from the O2 sensor switching from lean to rich. They change at about the same rate on the scanner.

I'm dealing with an HO here, but on the '91 the idle is always at that second line. It does not jump around for any reason. The only exception is fast-idle on a cold day. I don't remember what fast idle is for a 4.0 HO, but I don't remember the last time we had a cold day here in TN either.

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1 minute ago, Minuit said:

I'm dealing with an HO here, but on the '91 the idle is always at that second line. It does not jump around for any reason. The only exception is fast-idle on a cold day. I don't remember what fast idle is for a 4.0 HO, but I don't remember the last time we had a cold day here in TN either.

Mine doesn't move on the tach anymore. The scanner shows it does. The tach stays still even when the scanner says it's fluctuating.

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13 minutes ago, JMO413 said:

Mine jumps between 715 and 750 almost constantly.

Difference between 715 and 750 is 35. That's 35 rpm's. That number is calculated and per minute. Divide by 60 to get rps's (per second), like the way your reading it. Now it's not such a big deal.

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10 minutes ago, Ωhm said:

Difference between 715 and 750 is 35. That's 35 rpm's. That number is calculated and per minute. Divide by 60 to get rps's (per second), like the way your reading it. Now it's not such a big deal.

I'm fine with it doing it just wondered if someone else's does the same thing. I am truly thrilled with mine now! Just like to ask questions at this point.

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I'll take a video of mine running with the scanner plugged in tomorrow... if I remember :))

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13 minutes ago, Minuit said:

I'll take a video of mine running with the scanner plugged in tomorrow... if I remember :))

Awesome. Thank you.

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1 hour ago, Ωhm said:

AC ON or AC OFF, your idle speed should be the same. Your idle is high. My understanding is that 750 will be the target RPM's with engine at normal operating temperature.

The 2.5L is a weird animal. I have never had 750 idle except for once and that was due to electrical resistance from the distributor and the C101 

 

Idle has always been 950-1000. AC changed the game with 900-950 being idle. I’ve done all proper adjustments and still have never gotten a 750 idle. 

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6 minutes ago, eaglescout526 said:

The 2.5L is a weird animal.

My reference was for a 4.0L. Sorry, didn't read the fine print.

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20 hours ago, eaglescout526 said:

I’ve done all proper adjustments and still have never gotten a 750 idle. 

 

the  4 cylinder idles higher by design...

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Just now, omega_rugal said:

 

the  4 cylinder idles higher by design...

That's what I have always thought but wasn't sure, internet is flooded with info on the 4.0L. Wasn't until recently I watched nickintime and used my TBI manual to figure out that 1000 is a good RPM.

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On 10/4/2019 at 5:49 PM, eaglescout526 said:

AC on, 850-1000. Depends on warm up. Usually she likes 900-950. AC off is 1000-1100. Mostly 1000-1050. 

If your tach is correct, that's high. 

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My 2.5 I'd guess us 700-900.   Once I get the gas tank in I'll hook up the timing light and get an accurate #. 

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On 10/17/2019 at 9:02 AM, Comanche1 said:

My 87 2.5 has no idle cold, suggestions? When warm, it’s a perfect 800. 

 

check the IAC, the ECU controls cold idle with it, unplug it and see if it does the same or rpms drop...

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