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Idle speed going through the ROOF on warming up : 97 XJ 4.0 HO

MickeyS said:
but what is normal idle on an immediate idle at cold start? it's differed greatly between vehicles for me.
Click to expand...

Idle for the Renix XJ is 750 rpm. The first second or so does not really count, as the slow starts on the Renix usually have a little too much fuel the first second of running. Its the stable idle after 5 seconds that I would expect to see at about 750 rpm. But minor issues (imperfect grounds, TPS idle voltage off by .02 volts) can make it 600-900.... in park.
 
while ops 3k certainly is high, it takes at least 2 minutes in the morning for my 96 to come down to 750 from around 900 rpm on turnover. pretty sure this is normal as the ecu decides how much fuel to add before sensors are warmed up. my brand new rav 4 can hit 2k rpm on a cold morning for a good couple minutes as well. i always expected high idle regardless for a couple minutes
 
UPDATE: just spoke to the mechanic who, it sounds like, finally got around to trying to poke around a bit in my 92 XJ and they said that after some scanning etc it looks like the computer is calling for the IAC to 'go wide open' but apparently all the other sensors etc are all in spec so he doesn't know why this is happening. ANYONE ELSE here ever heard of such a thing? They are suggesting now that i take it in to the dodge dealership - which i'd really rather NOT do ...
 
NeXJ said:
UPDATE: just spoke to the mechanic who, it sounds like, finally got around to trying to poke around a bit in my 92 XJ and they said that after some scanning etc it looks like the computer is calling for the IAC to 'go wide open' but apparently all the other sensors etc are all in spec so he doesn't know why this is happening. ANYONE ELSE here ever heard of such a thing? They are suggesting now that i take it in to the dodge dealership - which i'd really rather NOT do ...
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Try cleaning the IAC. What happens if you leave the IAC unplugged?
 
boy it's been a while since i tested the IAC - i think i took it out and cleaned it though i may have replaced it - i remember trying all the suggested tests in the thread - i only remember deciding that wasn't the problem when i tried that ... but i guess the XJ will be coming back soon so i'll have to dedicate myself to DIY since the garage can't or don't seem willing to do it ... (ugh!) ... but wouldn't the fact that the computer is sending faulty IAC info (and the IAC and engine are responding in a rational manner) be a sign that the problem is not in the IAC itself in any way?
 


not sure if you saw my update .. what do you think i should tell the guy? to at least check the injectors etc before having it towed out ?? i told him your suggestions about the vacuum leaks and he said he 'checked around and didn't find anything' but that the computer was telling the IAC to go wide open (for some reason he couldn't fathom) ...

i just don't want to pay to get it towed somewhere else and have the same problems happen ... or to a dodge dealer and then REALLY get reamed ...
 
looking through the FSM i guess the AIS motor would be an obvious possible culprit since (i guess) it controls the idle speed directly ... although i'm not clear on whether a defect there would cause the computer to send the signals supposedly being read by their diagnostic tools (?)

help! :p
 
well the garage had it for FIVE WEEKS and didn't do crap except give me excuses and tell me things I already told them - in the end they told me to take it to the dealer - i guess they didn't want to be bothered with an older (92) jeep ... maybe they thought there was no money in it ** SIGH **


well back to square one now - trying to methodically go through my grounds but also wondering if maybe I shouldn't open up the ECU and have a poke around with the soldering iron -

does anyone have the opinion that i should definitely rule out my TPS or MAP sensors?
 
You either have a huge vacuum leak, vacuum lines, or the throttle body gasket or the Intake manifold gasket (loose bolts), or the IAC o'ring seal to the throttle body, or fuel injector o'ring seals at the intake manifold ports the FIs feed into. All can somewhat tested with a water spray to see if the idle changes.

Or a TPS or IAT temp sensor issue or ground sensor issue, or a FPR fuel leak into the vacuum (I think the early HOs still had the vacuum line to the FPR??? Not sure)

I would disconnect the TPS, IAC and O2 sensor connectors that got to the ECU and see if the idle changes, if not reconnect the IAC only and see if it changes and then report back.

Have you even tried checking the IAC to see if it is OK?
 
Ecomike said:
You either have a huge vacuum leak, vacuum lines, or the throttle body gasket or the Intake manifold gasket (loose bolts), or the IAC o'ring seal to the throttle body, or fuel injector o'ring seals at the intake manifold ports the FIs feed into. All can somewhat tested with a water spray to see if the idle changes.

Or a TPS or IAT temp sensor issue or ground sensor issue, or a FPR fuel leak into the vacuum (I think the early HOs still had the vacuum line to the FPR??? Not sure)

I would disconnect the TPS, IAC and O2 sensor connectors that got to the ECU and see if the idle changes, if not reconnect the IAC only and see if it changes and then report back.

Have you even tried checking the IAC to see if it is OK?
Click to expand...



THANK YOU for the advice - it gives me a short list at least - yes the IAC was one of the first things i tested ... bought a replacement just in case and swapped it out - no change ... (see early on in the thread - i know ... too much to go through) but yeah i did ... IAC and another sensor at the TB that i forgot now were the first ones i did

but thanks for keeping me on the right track ...
 
well - i'll be damned ... i just started it up a few minutes ago to see if my battery was finally charged (seems it was) and i ran it for 15-20 minutes and no acceleration .... (WTF?) - i guess i'll take my blessings where i find them and pray it doesn't return but I guess if this is going to be an intermittent problem it's going to be even harder to troubleshoot ... i'll have to cross my fingers for now!!!
 
i guess this must be the result of my having gone through the harnesses etc looking for bad grounds ... so im guessing the problem was electrical in nature (since no mechanical interventions seem to have had an effect) ... i guess at least it gives me a clue for future troubleshooting (if it shows up again ... start moving cables around and fiddling with grounds until it subsides ... then we will be closer to resolving it) ... well thanks for your patience and help everyone ... this wasnt such an easy case to crack
 
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