rough idle only when in gear

I could use a little help. My Jeep 94' Grand Cherokee six cylinder, is vibrating and idling rough when in gear (drive, or reverse.) The RPMs are okay and are not sparatic either. As soon as I hit the gas it runs just fine. It also idles just fine when in Neutral, or park. I thought it could be the engine mounts, yet it only idles rough when in gear, like when I am stopped at a stop light. Any ideas or suggestions.

try to put the AC on and turnt he wheel sluightly while idling in gear, if it gets worse the IDLE AIR CONTROL VALVE is going bad and not adjusting properly while idling.

I am having the same problem as described. I have done the test that dksob81 said to do, with no luck. All my hoses look to be in good condition, and do not hear any hissing noises. I have changed by spark plugs, spark wires, distrubtor button, and distrubtor cover. I have check all the things I changed, and everthing thing seems in great condition. I have an 1995 Jeep Grand Cherokee, I6 4.0 liter engine. Is there any other tips or suggestions?

Just to you let you know, I have checked the Idle air control valve. I have also cleaned the throttle intake and the idle air control valve.

Please Help Me!!!!!!!!!!!!!!!!!!!!!

lukecarr.

Does the RPMS drop when you place it in gear?from PARK or NEUTRAL. What RPM's does it idle at?

The rpms does not drop, when in drive or neutral. The idle rpms are about 500.

Check transmission fluid LEVEL.
Check with engine at normal operating tempature and transmission in NEUTRAL.

I did, the fluid looks clean and the level is at full. Some people told me the problem could be with using bosch 4 plantium spark plugs. Could this be?

altho i don't think that is the problem. you might want to replace them with the OEM CHAMPION RC12LYC, Bosch are junk for Chrysler products.

I had the Bosch plat +4's in my 94 ZJ and I notice my mileage drop dramatically. I put the CHAMPIONS back in and my milage went back up a lil.

I want to use autolite, is that a good brand? Just you let you know when I changed my sparkplugs, wires and dirstubor cover, and button my gas miles went up. I used to have a much more rough idle until I change the spark plugs. The rough idle has went down, but still notiable.

yea, I don't think the plugs are the problem, I just didn't see now increase in horsepower which I was expecting and my mileage went down alot, so I put new CHAMPIONs back in. The RPM's don't drop at all when you got from NEUTRAL to DRIVE/REVERSE?

Yeah that is correct, no change in rpms.

Check your motor mounts, putting it in gear will normally put more stress on the mounts. If one is snapped it will not be able to fully absorb the vibrations.

I also had the same problem as you, and would get worse when the weather was cold. Turned out to be low voltage to the fuel pump. Although it allowed it to run, idling at a stop light in gear, would produce a notied rougher idle with no lag in the tachometer. Got worse with time and ended up finally failing (PCM). Do you every have a delay or failure in starting due to low or non-running fuel pump?

I do not know how to tell if the fuel pump is running except for the wining sound before the engine starts. I do have the jeep running rouger in the cold. I also have a rougher idle in geer with not rpm change, just like you had. I do have a problem when it is cold outside sometimes I have give gas to get the engine to start. When it starts is sounds like it could stop, for a for seconds, then just rough idle. Most of the time when it is cold outside it does sound rougher. How would I go by to check the fuel pump out? Thank you for your time. Sorry it took me so long to reply.

Check your motor mounts, putting it in gear will normally put more stress on the mounts. If one is snapped it will not be able to fully absorb the vibrations.

How do I check my motor mounts? I am trying to learn.

let me check to make absolutely sure of the voltage that is supposed to run to the fuel pump. I'll write as soon as I know. I never tried giving it gas ,as it is fuel injected and should run at 40 psi continiously (if you have a gauge you can check this at the fuel rail port). Anyway let me check and I'll write.

I don't think it is the fuel pump. I just replaced it, it is running at 40 psi. Any other ideas for the rough idle?

Could it be the pcv valve being cloged, or the ccv valve being cloged? I do get oil in my air filter.

Yes deffinately
The PCV valve cause many slight rough idle problem. and it's only a few dollars. you could check it by pulling it out and shaking it if you can hear it rattling then it's good. You should be able to blow through one end but not the other.

If you gonna remove it, make sure to warm the engine first, this will loosen the rubber grommet to make it easier to pull out. I did this with the engine cold and end up breaking the PCV valve off.