Rough Idle Looking for expert Jeeper to solve problem

D

Dick

New member
1998 Cherokee Classic 4L perfect shape came from the south, just recently the engine is running rough in D/ R, I've done all the typical things:

New Copper plugs, distributor cap, rotor, plug wires,
Cleaned Throttle body
Replaced IACV sensor and TPS sensor.
Disconnected the battery for 1 hour to reset computer
Used stereoscope and listen to each injector
Checked for vacuum leaks
Used B12 in fuel tank

Were do I go from here: HELP REQUIRED!!!!!
 

Welcome to Jeepz.com
So it runs fine when you're in Park, but when you shift to drive what happens? Does it stall out, or does the idle just jump up and down?
 
TerryMason said:
Welcome to Jeepz.com
So it runs fine when you're in Park, but when you shift to drive what happens? Does it stall out, or does the idle just jump up and down?
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No, it runs rough in park/neutral/drive. While driving it runs smooth with power. Today check engine light came on, autozone says it is cylinder 5, ignition problem. I have already changed plugs, wires, distributor cap and rotor with no change in the idle. I added seafoam as suggested by autozone to clean the injectors. Not much is changed. Next thought is to change injector in #5 cylinder. Any other thoughts?
Thanks for responding, dick
 
Dick said:
No, it runs rough in park/neutral/drive. While driving it runs smooth with power. Today check engine light came on, autozone says it is cylinder 5, ignition problem. I have already changed plugs, wires, distributor cap and rotor with no change in the idle. I added seafoam as suggested by autozone to clean the injectors. Not much is changed. Next thought is to change injector in #5 cylinder. Any other thoughts? Thanks for responding, dick
Click to expand...

What code exactly? Knowing the code numbers gives a better idea of what is wrong and the tests to verify.

What brand and model plugs? What gap?

Did you clean the TB and IAC? The IAC directly effects the idle.

Battery cables and connections all clean and shinny? Battery fully charged and holds enough charge?
 

Hi, the Code was P0305, the code indicated cylinder 5 is the problem so I added some Sea Foam to the gas tank to see if it would clean the injector in cylinder 5 so far it's still running rough so I plan on changing the injector in just cylinder 5.

What's your thought of changing the MAP sensor

I installed Autolite Copper plugs, gaped at 30 thousands
Yes I changed the IAC,
Yes I cleaned the TB,it wasn't dirty but I still cleaned it ,intalled new gasket
Yes I clean the battery cables and used dielectric grease when I tighten the cables .
 
how about just move that injector to another spot to see if the problem moves. that would verify if the injector is bad or not?
 
i wonder if you have one of hte heads that are prone to cracking. my son's 98 ended up having a cracked head after the original also had cracked. we put an engine from a 99 grand cherokee in and zero problems.

we ended up doing the engine just because it was just as quick to pull a junkyard engine as it is to pull a junkyard head. and since the grand cheorkee said runs on the windshield, at least we knew it ran instead of wondering if the head would be good.
 

Your year requires single Pt plugs not copper. The gap should be 0.35. Be sure it is snugged down appropriately. Also on the IAC be sure the rubber gasket is in place and not torn or pinched. And the electrical connector is on properly. Beyond that pressure test the cylinder.

PS the P0305 is a misfire in cylinder number 5.

You might also check the intake Na exhaust bolt in 5 as they either loosen or break.
 
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Have you checked your cylinder compression? If not, do that real quick and make sure you are good there.

Do you have a vacuum gage? Hook that up and check your vacuum reading also.

Both gages are like 20 bucks each and can tell you tons of stuff about your engine
 
Hi, I did have PT plugs in there when the problem started so I called the jeep dealer and they told me the standard plug for my 4 liter motor is a Mopar copper core not PT, that's why I changed them to Auto lights copper but it didn't solve the issue. both types have experience a rough idle.

Thanks for your help,,Dick
 

Thanks for the idea, I plan on checking the compression today, I did check every hose for a vacuum leak using a carburetor spray cleaner, no hissing or idle speed chang noticed with the cleaner, I'll try a gauge.

Thanks Dick
 
google what the readings mean on the vacuum gage when you get it. my buddies truck started a rough idle and he was replacing things left and right. i put the gage on it and it told us what i thought the issue was the whole time, i cracked head or bad head gasket. we will have to tear into it sometime soon and find out but who knows when we will. we are on 7-10s at work so it doesn;t leave much work on vehicles time.
 
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