I have a 1997 Jeep Grand Cherokee laredo 4x4. I have had this hesitation problem with it when I first start it up( hot or cold engine temp, hot or cold air temperature outside). When I go to give it gas it sticks around 1500RPM and it hesitates and sometimes backfires , if you let up on the gas it will stop and you are fine. We have replaced plugs, wires, cap and rotor, Throttle Position Sensor,and the Fuel Pump, we also cleaned out the throttle plate with MAF cleaner, but the Grand Cherokee does not have a MAF. We can not nail the problem, it is a sporadic problem and it is a safety problem.
You should add a rs4 performance chip or the fuel economy chip also made by rs4. there like 70 bucks. If the problem is electrical changing your chip could solve the problem. Even if is doesnt work the chip will make your truck idle more smoothly, have better throttle response, and you will add 3-7 mpg. I bought one for my 1997 jeep grand cherokee straight six, and it felt like i was driving a different truck . It mae that much of a difference...you cant loose!!!Like everyone says , it could be a vac leak or a clogged fuel filter , soetimes bad gas...your problem is a needle in haystack. Try the chip...I hope this helps
Did you do any testing to determine if the parts you replaced were actually bad? At this point I'd recommend you get a chiltons, haynes or other manual with test procedures and expected values in it and follow testing outlined. I would also check for small vacuum leaks. A vacuum hose does not need to fall off to be bad. They can develop small leaks from dry rot as well. Check intake and every vacuum hose for leaks that can slightly alter fuel air mixture just enough to give you a problem. That includes any that run to firewall fenders and remote locations such as evap canister etc.
CCV orfice is easily cleaned out with carb cleaner and a short piece of wire. You can't not take stuff apart because you are afraid. i have several Jeeps in the family and though I've removed the orfice for cleaning many times, I honestly can't remember if it twists out or just pops out (I do it automatically...would go out and check but it's raining so hard I'd need scuba gear) One rule working with plastic parts...be gentle and use WD40 or other oily solvent and when you feel binding, look to see what or why before pulling harder. I've noticed that the connection on the valve end of the hose tends to open up a bit...I have a tie wrap around every one I have.
If you are concerned about dirt entering, wipe all around the grommet with a rag to clean it up before removal.
Aside from the ccv, you did all sensor tests? especially tps, map and manifold air temp?
Don't know if you read my profile but spent a long time with this stuff. Your problem stood out because I had just researched some info about that and also had pretty much the same thing after changing oil on one of our jeeps...knocked a line off the canister on the passenger side canister near the firewall while worming the filter out. But, that can happen with any vac line. PS the map sensor is on the firewall not in the throttle body, Idle control valve is right next to the tps and also can get dirty inside the passage...one thing though, don't turn the valve pin if you clean that.
A rubber hose that has a small crack can sometimes stay together and cover up the problem intermittently. But the problem can be just about anywhere ...that's why I mentioned testing everything. Think it's hard doing that when you are in front of the car? try telling someone how to tie their shoes over the phone! That's why unless someone has a specific problem (like changing a part) it's so difficult to do online diagnosis when it's often difficult even when you are there and have all the diagnostics equipment at hand.
If you look through other posts, 90% or better are strange electrical problems...most go unanswered because it takes careful hands on diagnosis to get to the bottom of those problems...I'm crazy enough to answer some of them and wind up with a headache for it!!!
Keep me posted on what you find!!!
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Change spark Plugs Wires distributor cap rotor needs to be replaced. If that doesn't solve it, then it's the coil
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Yes I do have a Haynes repair book. I have tried to check the CCV system but I do not want to break any of the lines or get any foreign materials or the rubber grommet down into the valve cover. I was just reading a thread somewhere saying that it is easy to repair and you can go to the dealer and they have a whole kit with new hoses and rubber grommets to replace all of the old CCV components. I have read in the Haynes book that a vacuum leak can cause engine misfire and hesitation so maybe that is it. My Dad and I also think it could be something that is down inside of the distributor either the pickup or the Camshaft position sensor, He had this problem a ways back on an 88 S-10 Blazer. So as you can see I am stuck. Thanks For your help.
Yes I do have a Haynes repair book. I have tried to check the CCV system but I do not want to break any of the lines or get any foreign materials or the rubber grommet down into the valve cover. I was just reading a thread somewhere saying that it is easy to repair and you can go to the dealer and they have a whole kit with new hoses and rubber grommets to replace all of the old CCV components. I have read in the Haynes book that a vacuum leak can cause engine misfire and hesitation so maybe that is it. My Dad and I also think it could be something that is down inside of the distributor either the pickup or the Camshaft position sensor, He had this problem a ways back on an 88 S-10 Blazer. So as you can see I am stuck. Thanks For your help.
Okay I will try that, yes it is raining like crazy here so not today. I have replaced the TPS, but Have not yet tested the MAP and IAC, tho we cleaned out the throttle plate and sprayed MAF cleaner into the throttle body where we believed the MAP sensor was. Have not had alot of time to test these sensors with weather, college and work.Did you have this problem on Your 4.0L also or do you just know of troubleshooting procedures? Thank You very much.
Yes I did read your profile, impressive. I will definitely look into the CCV and the all other possible vacuum leaks. Hopefully that is it. Though I do not know why it would not be doing this all of the time if there was a leak, like I said this is a sporadic problem, which has not happen in a week or two. Thank You very much. My Dad who has worked on cars for 30+ years could not nail the problem, our mechanic could not solve it and we are about to take it to the dealer. With this info I will look into the CCV system and hopefully not have to call the dealer. Thanks again.
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