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Old 06-10-2011, 07:23 PM   #1
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no idle in heat

I have been fighting a gremlin for over a year now.... when the weather here Is around 88 to 90f.. it runs great at driving speeds but sometimes when i slow down and allow idle(downshifting, stop) it will start to sputter and can stall. if i push on the gas it will almost always cause the stall and if i let it do its own thing for about twenty to thirty seconds it will catch up by revving up to about 1025 rpm, then dropping back down to normal... if i am still waiting on the light i have about 30 seconds until it jumps back into this problem and we wait again.it will only happen on 80 degree+ days. all this winter i have never had the issue and last fall i thought that i had fixed the problem, i guess it was just too cool for the problem to show up again. my jeep has new plugs wires cap rotor, new crank sensor, new fuel pump, new battery, fuel dampener,idle air controller and coil. i have also been very cautious to let any exhaust leaks by watching my exhaust/ intake bolts, no sign of any exhaust leaks.i have checked my tps with a genisis computer and not found any fluctuations, hot or cold. no codes are currently present and cel never pops on or off during the problem issues..
Any help would be immensely appreciated

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Old 06-11-2011, 09:23 PM   #2
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Take a peek at the TPS (throttle position sensor) if it has a bad spot it can send erroneous signals to the ECM. The ECM doesn't know what's going on and can't compensate. Check it with an ohm meter, resistance readings should go up down smoothly as the throttle is opened/closed. If it skips a spot or blanks out, you got a bad TPS. Heat can affect it, as heat causes material to expand, and it may be causing the TPS to bind.

Also look at the injectors. On the 6's they have asbestos shields around them on the intake manifold, to help block the heat from the exhaust manifold from affecting them. If the shields have deteriorated or are missing, you could be experiencing good old vapor lock.

The fuel is boiling in the lines from the heat at low speeds/sitting still.

When you're running at speed, the fuel is flowing fast enough to not be affected as badly. Slow speed or sitting at idle, the fuel need is less, so the fuel sits and soaks up all that heat. After it runs a while the cold fuel coming in starts to cool the hot lines enough you start getting liquid fuel instead of fuel vapors. The ECM meanwhile is commanding wide open injectors to get the idle back up, and as soon as the cool fuel hits em the idle screams up before the ECM can catch it and adjust it back down.

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Old 06-13-2011, 06:51 AM   #3
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The tps has been checked, hot and cold..very smooth.the heat soak issue could be very likely. I tried some insulating wrap on injectors, rail and lines last night..see how it does today
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Old 06-13-2011, 09:13 AM   #4
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If the computer's temp sending unit is wrong - defective, wrong one, miscalibrated, etc it's lying to the computer.
If the computer "thinks" the engine is too hot (based on the lie,) it will try to cool the engine down by revving it up and changing the timing.

Put a scanner on it that can see the data stream from the computer - watch the temperature reading - that is what the computer "thinks" the engine temp is - it's the INTERPRETED VALUE, not necessarily the reality.

Sounds like the computer and the IAC are doing their jobs correctly. It's not setting a code because the range is within specs, but just inaccurate.

It's not possible to make correct decisions based on lies. Just look at the news media - if we actually knew the real truth most of the politicians we have now would be in jail!
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Old 06-13-2011, 09:20 PM   #5
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My actual gauge shows right where it needs to be..and to my knowledge ,correct me if I'm wrong ,the computer on a tj is what supplies the info to the gauges.
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Old 06-13-2011, 09:22 PM   #6
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And on a side note the temp listed on the scanner have always matched up...
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Old 06-15-2011, 05:32 PM   #7
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By another throw in the dark could the map sensor be causing these odd issues?
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Old 08-03-2011, 06:20 PM   #8
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Today has been a heavier set of shutdowns....while driving in 101 temp it was shutting down while in gear..highway speeds or city driving..

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