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Chrysler Repair/rough idle on 94 Grand Cherokee Laredo 4.0 L

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QUESTION: I have a 94 Jeep Grand Cherokee Laredo 4.0 L 4x4.
I have a mild rough idle all the time hot or cold.
Sometimes when first started hot, runs very rough till I take off or shut off and restart engine, then mildly rough again.
engine has great pick up and runs good ( I am getting 21 MPG ) once you hit the gas till you stop and go back to idle.
This happens in Park or any gear at Idle.
I have replaced the fuel pump, fuel filter, pressure regulator, Dist. cap, rotor, plugs, coil, air filter and wires. this started after I had a fuel pump replace 4 months ago by a repair center. As of 2 weeks ago, I now also have a inaccurate fuel gauge and excessive vacuum in the fuel tank. Upon testing the fuel system, I have 42 lbs. pressure at idle to the fuel rail.
please help on this problem. I am thinking a faulty fuel pump assembly but don't want to put extra money if not needed.
Thank you for any help,
Rick

ANSWER: Hi Rick,
Try to take advantage of the self-diagnostic capability using the ignition key: "on-off-on-0ff-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains "on", to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat the process to be sure of an accurate set of flash counts. Then let me know the counts in order of appearance. We'll go from there.
Roland

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QUESTION: Roland,
I checked the computer and only code is a 55

ANSWER: That being the case, Rick, I would suggest that you find the exhaust gas recirculation valve which typically is located in a narrow-diameter pipe which branches off the right exhaust manifold and is routed to the throttle body area. In that pipe you will find the valve which has a round top with a vacuum line and between that and the body of the valve is a flange which conceals the valve stem. The stem has a slot which you can insert tip of a screwdriver into and thus move the valve stem back and forth. That 'action' can become gummed-up so that the valve will not close tightly at idle. So take some WD-40 and spray it on the stem where it enters the body of the valve and then move the stem back and forth to free it up. This often works to deal with rough idle and the absence of fault codes.
Roland

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QUESTION: Roland
Thank you for this advice. I will check this as soon as it stops raining here.
do you have any other ideals on the extremely inaccurate fuel gauge ( I ran out of gas last week and the fuel gauge was reading 1/4 tank ) or the very excessive vacuum in the fuel tank?
Rick

Answer
On the fuel gauge, the sender inside the tank may not be moving down along with the actual level in the tank. You might check to see if that is a separate sensor or is part of the fuel pump. I don't have a manual for that vehicle so I can't tell you. On the vacuum level in the tank: what is the extent of the level and how it compares to what it should be would be the question. The tank is certainly sealed against vapor escaping and so there is also some level of vacuum, but again I don't have the manual to evaluate that.
Roland

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Roland Finston

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Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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I was voted "Top Expert" 2010-2015, here at AllExperts, and have answered 20,000+ questions.

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Five decades as a 'do-it-yourselfer' on domestic and imported cars.

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Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

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Advanced degrees in Physics/bruised knuckles

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"Top expert" of 2010, 2011, 2012, 2013, 2014 and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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