Map sensor

[byrinxx74]

Ok so i have been having trouble trying to figure out my idle shake. I have posted on so many threads what to do. Though everything that i have tried has made no diffrence. cap,rotor,cables,plugs,iac,tps,seafoam,fuel pressure test,fuel filter,clean throttle body, motor mounts. Still nothing. No codes, drives fine when you hit the gas. I have had other guys with jeeps take a look to see if i was crzy and they say the same thing that there is a slight miss. So today i tried to unplug the map sensor by the throttle body, while the jeep was running, it really did not seem to make a diffrence though when i went back into the cab the check engine light came on!! I plugged it back in though still check engine light? So my question is this. Could it be the map sensor that is causing the rough idle. Also should the check engine light come on for the map sensor.

[Mudderoy]

Ok so i have been having trouble trying to figure out my idle shake. I have posted on so many threads what to do. Though everything that i have tried has made no diffrence. cap,rotor,cables,plugs,iac,tps,seafoam,fuel pressure test,fuel filter,clean throttle body, motor mounts. Still nothing. No codes, drives fine when you hit the gas. I have had other guys with jeeps take a look to see if i was crzy and they say the same thing that there is a slight miss. So today i tried to unplug the map sensor by the throttle body, while the jeep was running, it really did not seem to make a diffrence though when i went back into the cab the check engine light came on!! I plugged it back in though still check engine light? So my question is this. Could it be the map sensor that is causing the rough idle. Also should the check engine light come on for the map sensor.

Yeah I would expect a CEL light to come on if a sensor is unplugged. I don't know that it should, but I would expect it.

I have the same rough idle situation. I'm going to try replacing the coil tomorrow, just because I have one and it's not that hard to change.

[Brasscatz]

The check engine light on OBDII engines is designed to come on for any issue related to emmissions. A loose or missing gas cap can trip the light as well. Since it is on, that can definitely help. When you have time, take it up to your local auto parts store, Auto Zone, Advance Auto, etc, and have them pull the code(s) for free and that may get you a step closer. The other things I would check would be crank position sensor, and check for vacuum leaks. O2 sensor could also do this and a diagnostic should reveal a code if this is the issue. Should reveal a code for the CPS as well. It is possible to a have a code or 2 without the CEL being on, so since it just came on you may still have more than 1 code.

The probability that you will have other codes is fairly low since you had zero codes before, but it's a possibility. You can disconnect the battery for a few minutes to clear the codes yourself, then see if it comes back on after a while of driving. Another question... what RPM does it idle at currently?

[byrinxx74]

Idles at 750 800. RUNS GREAT! While your on the gas:bang: Its just when at a stop it will seem like a slight miss? It will shake then try to correct it self and repeat.

[Brasscatz]

Hmm... mine has what feels like a miss in it too at idle... like at a stop light but it's just a small random "bump". I did a full tune up on it as well and it still did it. So now I flashed my pcm and I'm waiting to see if that does anything.

Is it a bad shake or a little bump/hitch? Does the tach waver when it happens? There is also a ground on the back of the valve cover on one of the bolts... might want to clean the contacts on that one. There is also another ground, but I can't remember exactly where it is atm... Somebody else here probably knows.

[4.3LXJ]

Check your timing. That issue can cause a late model fuel injected motor to have those issues. There is an article on here by Mudderoy on setting the timing. in the dizzy.

[byrinxx74]

Ok thank you. Its a little notch at idle, like it would shake then try to correct its self. Could it be motor mount problems. Also timing really, i will try that.

[Brasscatz]

I don't think it's the motor mount... unless it does this:

http://www.youtube.com/watch?feature=player_embedded&v=RVwZHn6ISr4