JMO413 Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
Minuit Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 5, 2019 Share Posted October 5, 2019 AC on, 850-1000. Depends on warm up. Usually she likes 900-950. AC off is 1000-1100. Mostly 1000-1050. Link to comment Share on other sites More sharing options...
Ωhm Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
JMO413 Posted October 5, 2019 Author Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
JMO413 Posted October 5, 2019 Author Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
Minuit Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
JMO413 Posted October 5, 2019 Author Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
Ωhm Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
JMO413 Posted October 5, 2019 Author Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
Minuit Posted October 5, 2019 Share Posted October 5, 2019 I'll take a video of mine running with the scanner plugged in tomorrow... if I remember Link to comment Share on other sites More sharing options...
JMO413 Posted October 5, 2019 Author Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
Ωhm Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 5, 2019 Share Posted October 5, 2019 Just now, Ωhm said: My reference was for a 4.0L. Sorry, didn't read the fine print. No worries. Link to comment Share on other sites More sharing options...
omega_rugal Posted October 5, 2019 Share Posted October 5, 2019 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... Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 5, 2019 Share Posted October 5, 2019 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. Link to comment Share on other sites More sharing options...
omega_rugal Posted October 5, 2019 Share Posted October 5, 2019 4 cilinders usually idle at 900-1000, inline 6 700-800 and v8s can go as low as 500 rpm Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 6, 2019 Share Posted October 6, 2019 1 hour ago, omega_rugal said: 4 cilinders usually idle at 900-1000 Then I'm good to go. Link to comment Share on other sites More sharing options...
Wounded_Fighter Posted October 10, 2019 Share Posted October 10, 2019 Somewhere between 500-1200, depending on how she feels that day Link to comment Share on other sites More sharing options...
Comanche1 Posted October 17, 2019 Share Posted October 17, 2019 My 87 2.5 has no idle cold, suggestions? When warm, it’s a perfect 800. Link to comment Share on other sites More sharing options...
cruiser54 Posted October 17, 2019 Share Posted October 17, 2019 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. Link to comment Share on other sites More sharing options...
WesD Posted October 19, 2019 Share Posted October 19, 2019 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 #. Link to comment Share on other sites More sharing options...
Wallace Krempa Posted October 23, 2019 Share Posted October 23, 2019 I know that i have injector issues, but with my 4.0 it runs about 1200 cold, and about 900 warm. Link to comment Share on other sites More sharing options...
omega_rugal Posted October 23, 2019 Share Posted October 23, 2019 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... Link to comment Share on other sites More sharing options...
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