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93 Jeep Grand CHerokee 4.0. Low, rough idle after changing motor mounts

posted Jul 11, 2016 18:03:02 by AaronGustaveson
Ran well before changing motor mounts. Starts quickly and rpms jump to 1,500 rpm then settle at 1,00 for a few seconds before dropping to around 550 rpm,(where the idle is rough and causing vibrations)Off idle, jeep seems to run well. Rough idle only occurs when stopped. If I am driving down the road and allow the jeep to slow to idle, it will maintain 1,000 rpms and idle smoothly. When stopped, the idle drop to 500-6-- rpm and is rough. THis i true even if I stop using only the ebrake. Idle is rough in any gear, foot on or off the brake.

Ive inspected the vacuum lines and elec. connectors extensively. No stored codes. Cant find any vacuum leaks using throttle body cleaner or propane. I have a vacuum gauge but am not trained at interrupting it.
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5 replies
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AaronGustaveson said Jul 11, 2016 18:03:42
*settle at 1,000
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Chris said Jul 11, 2016 19:13:56
Do you have a scan tool that does live data? I seen multiple TPS failures at DONT set codes and are a bear to pinpoint with out a scanner. If it's faulty you'll see the voltage from the TPS jump around a little causing a rough idle and possibly a stall condition.
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AaronGustaveson said Jul 11, 2016 19:51:31
Unfortunately I do not. I would love to own a scan tool, but the descriptions of feature provided by manufacturers are so vague that Im afraid to purchase one. I really need advice on which one to buy.
This particular jeep is OBD1, just to be clear.
I have seen a bad TPS on this jeep before. The symptom was the jeep seeming to "die" for a fraction of a second, periodically at highway speed.

I know that I could coincidentally have a bad TPS all of the sudden, but the jeep did not have this issue before I did the motor mounts.

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Noah said Jul 11, 2016 23:19:51
Only in gear, or in park also?
Massachusetts, USA
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AaronGustaveson said Jul 12, 2016 16:37:58
In park as well. The only time it idles without being low and rough, is if the jeep is actully moving down the road at idle. In that case it will idle down the road at 1,000 - 1,1000 rpms and run smoothly. But in order for that to occur, I must first give the jeep a little throttle, to get it moving ,then decelerate to idle speed.
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