Check Engine Light

[RedWings44]

Everything seems to be fine...I just was wondering if anyone could inquire about this.

A few days ago, my CEL came on. The code was P1151...something about lack of switching, etc. Only driving issues I noticed is the opposite of what everyone usually complains about. The typical thing is their cars idle too low and almost stall on several occasions.

Mine does the opposite at times instead. It will idle at 6-700 in park at its lowest, or at a stop light at its lowest..but it will most of the time (when it isn't running normal) idle too high, causing excessive speed (40+) when I'm not on the gas and in a city...which causes me to ride my brakes. My worst case so far was a few weeks ago when I put it in park and she was idling at 1600 (higher than my normal driving)..which had nearly caused me several accidents at intersections. Usually it won't go that high though. This was with the light off. Anyway, those are just the symptoms, and it doesn't do it all that often. This is caused by the engine correcting for a perceived lean condition when there isn't one.

Back to what I was saying, the light came on and it spat out that code (my rambling was the typical, and my symptoms)...the thing is, I didn't do anything and the light turned off today. I wouldn't say anything normally, but it did this once last year as well. What do you guys think? Is there something I should check? Or should I just call it good until it comes back on again?

 

[wmburns]

Almost surely you have a vacuum leak. The vacuum leak is causing the high idle and the P1151 DTC.

Here's some more information on how to trouble shoot idle/IAC issues. However, it won't help much until the vacuum leak is found and fixed.
http://www.allfordmustangs.com/foru...-dieing-idle-idling-rough-14.html#post2260649

Here's some information regarding a "cheap" way to perform a smoke test.
http://www.allfordmustangs.com/foru...-dieing-idle-idling-rough-16.html#post2942011

 

[RedWings44]

Thing is, that is one of the possible causes...the other things make sense to me as well. How come the light turned off then? (No I haven't checked to see if the code is still there yet)

 

[Killian Korth]

codes will randomly disappear on mine too for some reason, I've had the EGR flow being shown as too great and insufficient (at the same time) for as long as I can remember and then one day the codes will stop and the light will shut off.

My guess is that the vacuum leak isn't extremely terrible yet, and in that case it somehow sealed again temporarily. It'll most likely leak again.

 

[RedWings44]

Ya, my light came back on last night. Almost every possible cause I've heard makes sense to cause the high idle. However, the times it idles normal, high, and low seems too inconsistent to be a vacuum leak. I'm thinking some sort of sensor. Could be the MAF or the O2. I haven't had the time to check the code this time. I was too busy being pulled over for the tint on my front windows lol. It is a light tint. My understanding of the law was (given by the previous owner who had a friend who was an officer) that if you can see in from the outside that it was ok. Apparently that isn't it. Anyway, I'm rambling again.