Issue, Rough idle and power loss -
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post #1 of 5 Old 09-01-2014, 10:19 PM Thread Starter
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Issue, Rough idle and power loss

Hello everyone,

So lets get right into this, I recently bought a 1993 grand cherokee laredo with the 4.0 straight 6 and automatic 4 speed transmission. She takes longer than usual to roll over but that is not the real problem. The same day i bought it I put about 150 miles to get to college then the problems started. Once started it idles kind of rough, like it vibrates rough, and once put into gear the vibration gets about twice as worse but it seems like in reverse its the worse but once moving it smooths out until i come to a stop. Didn't drive it for a week or two until I got to go home this weekend. Half way through the two hour trip at speeds of around 40-55mph it started the same vibration as when it idles when trying to go a constant speed, if over drive is turned off the vibration range goes to 30-45mph. If no gas is given at all or making it accelerate quick, if it down shifts that is, the vibration goes away completely. I get home and over the next day it seemed to have loss all its horsepower and acceleration and sometimes vibrates at certain speeds accelerating but not always. No matter what as soon as it downshifts the whole this smooths right out. Now I can put the pedal to the floor and the rpms and speed will slowly rise like i am barely giving it gas. Going up hills i can put the pedal to the floor and it will not always downshift to make up for the lack of power to make it up the hill, sometimes i have to release the gas and press again to make it downshift. The pvc hose was slightly melted near where it comes out the valve cover and was clogged with gunk. Over this weekend it has had the oil changed, transmission fluid changed, spark plugs and wires changed, did the diagnostics check and it came up with a bad map sensor so i replaced that also, took carb cleaner to the IAC and TPS and the throttle body since they were also gunked up, which i think it is gunked up because of the other hose that runs from the valve cover to the air filter box right above the filter. I don't think i have a vaccuum problem since the throttle body is sucking pretty hard. Put some seafoam in the oil and gas which is suppose to help clean the gunk out but nothing has helped so far. Even though all the problems have happened my mpg hasnt been affected, drove 125 miles back to college like this and only burned about an 1/8th a tank of gas over lots of hills. So to sum up my problems are vibration while at idle and constant speed anywhere from 40-55 mph and complete loss of acceleration and horsepower. Thinking it might be a transmission problem now instead of sensors, would love some other opinions, input, or even other questions about it.

Thank you

Last edited by Seanypat14; 09-01-2014 at 10:22 PM. Reason: added info
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post #2 of 5 Old 09-06-2014, 09:33 AM
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another possibility is the fuel pressure regulator....pull the vacuum hose of the fuel pressure regulator,if the hose has gas in it,its wasted and needs replacing

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post #3 of 5 Old 09-06-2014, 09:39 AM
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Check and recheck all of the vacuum lines. Replace the fuel filter. Clean the injectors, test them.

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post #4 of 5 Old 10-01-2014, 07:47 AM Thread Starter
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Well I never did check those things but I noticed the shake is kind like when you are in to tall of a gear I put in first at a stop and start to go it's pretty smooth, get up to speed and shift into second and its smooth, shift into drive with overdrive off still smooth,with over drive it rides smooth above 60mph, still no power at all if there is the slightest incline( and I mean slight) I will lose speed and won't be able to get back up to speed unless I make it up the hill or downshift before I make it up,so I'm beginning to think I have a tranny problem and my engine is shot, yet to do a compression test either any tips on how I could do that myself?
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post #5 of 5 Old 10-01-2014, 07:58 AM Thread Starter
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Almost forgot that I went to a few garages and they said I had cylinders not firing,finally replaced cap and rotor which did need changed but still no difference.
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idle problems , loss of power , vibrations

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