Rough Idle

Hey guys i have a 90 XJ 4x4 with the 4.0l inline six with the auto trans. Yesterday it started idling really rough i estiamte between 400 rpm and 800 rpm approx. Today i replaces the plugs, cap and roter with no real improvement. As the timing is conrtolled by the computer, is there any thing that has to be done after replactin cap rotor and plugs ?

Also any other suggestions on what to check ?

Thanks in advance :bananasmi

Chili

chili, start by checking for disconnected vacuum lines and/or damaged vacuum lines. If all is good check your air filter, oil, and fuel filter. Is there any background to this problem?, is there any difference in drivability?.

clean your throttle body and iac valve located on left side of throttle body, if is is all black, this should give you an improvement

clean your throttle body and iac valve located on left side of throttle body, if is is all black, this should give you an improvement


Ok noob question for you......does anyone have a good picture of the IAC ? and how should you clean the throttle body ? Spray Carb Clean on it ?

THanks

Chili

Ok noob question for you......does anyone have a good picture of the IAC ? and how should you clean the throttle body ? Spray Carb Clean on it ?


I just take carb cleaner, a rag, and elbow grease and make the that thing as shiny as possible. You can easily open and close the throttle plate while cleaning. There is a little hole on the air intake side of the plate that leads to the iac, I just stick the little tube it comes with up into the hole for the iac and spray away until no more black comes out. It ussually takes a bit longer to start after this procedure, but no worries it will be fine after that.

I haven't tried this on my jeep yet, but I read and performed a little trick that i learned from some other forums on my saturn that really helped the idle/ride. It basically amounts to soaking the the combustion chambers with Marvel Mystery Oil in an effort to get rid of some of the crap built up and allow the pistons to move a little more free. You can read about it here...

http://www.saturnfans.com/forums/showthread.php?t=23676&highlight=mmo+soak

Ok guys the problem seems to worsen:

Today the wife got in the jeep and ran to hte store and came back with about the same level of rough idle as before but now i looked in the driveway and street and there are patches of BLACK splatter from the exhaust. So get in the jeep fire it up and rev the motor to about 2500 rmp and clouds of black smoke roll out of the tail pipe.......any clue what could have caused this drastic change in performance ? Just got it smogged EXACTLY a week ago and the mechanic said the motor smogged just like a brand new motor....what gives ?

Chili :banghead:

Ok guys the problem seems to worsen:

Today the wife got in the jeep and ran to hte store and came back with about the same level of rough idle as before but now i looked in the driveway and street and there are patches of BLACK splatter from the exhaust. So get in the jeep fire it up and rev the motor to about 2500 rmp and clouds of black smoke roll out of the tail pipe.......any clue what could have caused this drastic change in performance ? Just got it smogged EXACTLY a week ago and the mechanic said the motor smogged just like a brand new motor....what gives ?

Chili :banghead:

Check your egr valve operation. The valve should not open at idle speed.

Well, if i'm not mistaken black smoke typically means that you are running to rich and not burning up all your gas... I would suspect that your gas mileage is terrible as well, no? Did they make carb's in 90'? If so, I would check that. Other things that can cause black smoke... vacuum leaks, bad pcv/ccv valve/setup. A plugged cat converter can also cause this.

Hope this helps

chilli,
what have you done, we know about cap plugs ect..have you tried any of the several sugestions? this will help us to help you

chilli,
what have you done, we know about cap plugs ect..have you tried any of the several sugestions? this will help us to help you


OK got if figured out......was a broken vacuum line off the throttle body leading to the sensor mounted on the firewall (cannot rember what the hell its called :dunno: ) lolbut hey it works :D

thanks all for the input

Chili