Filled tank with gas and rrove about 50 miles. Went to a meeting and began driving back home. The engine misfired or hesitated, then ran OK.
About half way home the "CHECK ENGINE" LIGHT CAME ON STEADY. but the truck ran OK.
After about 4 days the light remained on so I had the dealer read the error code. It indicated that the Mass Air Flow sensor was out of range. They recalibrated the sensor and the light went out. They said that "sometimes" this will fix the problem.
It fixed it for one day and the light came back on. The mechanic also asked me what grade gas I was using. I told him mid range and he said it was OK to use 87 octane instead. So I switch to 87 or regular.
In the meantime I cleaned the MAS with an utrasonic cleaner (the type you clean jewery with) using purified water and then dried the sensor with air.
(suggested by an Engineer that manufactures MAS's for another company, Not Bosch)

Now the light is off part of the time and on part of the time. I will be switching back to mid grade gas ASAP.

Now I don't know if it's the MAS sensor or the regular gas.

Anyone have any input? Is gas Octane a real potential issue?
Thanks

when the CEL is on, you have to have the codes read, even if only by someone at AutoZone (they'll do it for free with a universal OBSII device). if you're throwing codes 1073 and/or 1077, it's probably a bad MAS [your cleaning technique is intriguing, but most posts I've read don't give me much confidence in any cleaning method]. do a search of CEL or AMM, MAS or MAF; somewhere there's some great advice by blackmercedes that pertains to replacing the air filter and cleaning out it's housing often to avoid fouling the MAS. if you don't want to spend the $300 for a new MAS, try ebay: I just bought one for $40 and another for $30. but correct the fault first, or you'll just fry another MAS.

__________________
2002 C230 Coupe + 2003 C320 4Matic Sport
http://img.photobucket.com/albums/v1.../sigpic5-2.jpg

I appreciate your help on the issue.
Currently the CEL is off again so if I were to replace the MAS while the light is out or off, will I fry or damage the new MAS?

I do have a local Auto Zone so if it comes back on I could have the codes read.

Also just filled up with med range gasoline.

Thanks again

I'm a little baffled by the on-and-off nature of your CEL (of course, I am mechanically inept); but I would at least try to clean out the air filter housing, maybe even clean the MAS again (I might try that jewelry cleaner technique with my old MAS, which I didn't have the heart to throw away). another great post re: this issue was by stevebfl, who posted a link to a superb article--technical but informative. search.

__________________
2002 C230 Coupe + 2003 C320 4Matic Sport
http://img.photobucket.com/albums/v1.../sigpic5-2.jpg

Interesting, the one thing I forgot to mentioned is this whole situation happened shortly after the 50,000 service performed by the dealer. Maybe some dirt did get jogged around in the air intake.

Well I'll let you know how it goes over a week or so.

Right now I'm going to let the high octane gas get into the system and keep my hands off !

Regards

Just a quick contribution to this CEL thread. It seems that my 99 320 has had this malfunction light on for about 75% of the time since it was a year old. Four different shops have read then cleared the codes but the light always came back on within a week. At different times I've been told that the MAS or the purge valve may have been at fault. Codes reported to me include: PO300, 301, 130, 135, 170, 173, 302, 303, 442.

The purge valve was replaced about two years ago but the CEL was not out for long. Last summer when the MAS signal was again reported out of range, it ws changed. Following replacement of the MAS, the light stayed out -- for about a hundred miles.

In all this time, the vehicle has only stumbled once (while trying to pass a truck about two years ago). Otherwise, the engine has responded well and still sounds as smooth as the day of purchase. Gas mileage seems reasonable (but I should formally check it). Although I was originally concerned about the CEL being on, I've just learned to live with it. The shops involved haven't conveyed any urgency so no sense in loosing sleep.

Thank you for sharing your experience on the CEL.
Well I'm going to replace the MAS sensor. Found one new for under $200.00 so I'll see what happens. Maybe I'll get the black tape out and cover the light up if that does not fix it. ML is running OK so far.