W140 Idle Surge

[Aaronguy]

My car has started to surge whenever I am at idle. In the last few days it has gotten worse and now its shakes so hard that it feels like the power is getting sucked out it and its about to cut off; I have to give it some gas just to balance it out so it will not cut off. The car tends to be even weaker when the a/c is on. So far it has cut off once at start up with the a/c on. One last thing! I noticed that on the freeway the car runs smooth for the most part but sometimes flutters a choke as if there is a glob in the fuel line or something. I just had my tune up all spark plugs changed and I cleaned my fuel line with fuel system cleaner so I dont think its the fuel system. According to the owners manuel these cars need at least 91 octan fuel and I do admitt that I had been running it on 89 to 90 octane fuel for the past few months because thats all premium gas is in most parts but I still think that me putting 93 octane premium fuel for the last 2 weeks would have fixed this. The only thing I can think of is it has to do something with the air intake regulation sensor though I am not sure. Please let me know if anyone is familiar with this problem your advice will be taken gladly. Thank you guys for your time and have a great weekend!

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[Rod Spohn]

There is a fuel pressure sensor on the front of the engine. On Drivers side, Pull the Vacuum line and smell it. If you see or smell gas its going bad. Good thing is it’s a easy and inexpensive thing to fix.
The other thing that comes to mind is a bad coil. Are you getting any error codes.

[Aaronguy]

No I havnt got it diagnosed yet but that fuel pressure sensor sounds like a good thing to try out. I will unplug it and see if it smells!

[dickster601]

Originally Posted by Rod Spohn

There is a fuel pressure sensor on the front of the engine. On Drivers side, Pull the Vacuum line and smell it. If you see or smell gas its going bad. Good thing is it’s a easy and inexpensive thing to fix.
The other thing that comes to mind is a bad coil. Are you getting any error codes.

my car is doin the same thing. when you first crank it up it runs perfect and all of a sudden it starts to cut off. its like its loosing power goin down the highway even if you punch it.. also, there use to be a horrible gas smell coming from it. it was impossible to be inside or outside of it while its running..
what do i need to do.. also, how can i turn the top end speed up from 137. i want to get it around 150.

[JNLeChevet]

Had the same problem a few years back and it was the Mass Air Flow sensor. You should get a check engine light if it is the MAF.

[Rod Spohn]

dickster601- yours sounds like a differant issue than the fuel presure regulator! The Gas smell would worry me if its as bad as you say. I'm guessing you would have said if you had gas dripping from someplace. The fuel filter is just in front of the rear wheel on the drivers side and the rubber hoses may be weathered. I would still check the presure regulator - where my experiance I wasn't getting enough fuel maybe it can also go bad the other way and put out to much and the smell is the fumes coming out the tail pipe. Good luck.