M104 P0170 Fuel Trim
 

CEL illuminated yesterday, just a few miles ago. MAF replaced about 130 miles ago due to backfiring and a flat spot when accelerating; CEL was not on when experiencing those issues. After replacing MAF, car drives perfectly but now the CEL has come on. Got the P0170 code from AutoZone; it is the only stored code.

I should mention the car takes an extremely long time to start when it is hot, maybe a 5 to 10 second crank. This problem was there before replacing the MAF, but was not corrected with the new MAF.

Should I be suspecting the regulator?

yes,I thought better to be a check your suspecting the regulator

Took off the vacuum line and sniffed it, it does smell a bit like gasoline. Not strong, but definitely there. Is this normal since the vacuum line isn't very long and taps right into the intake manifold? Also started up the car with the vacuum line disconnected; did not observe any fuel flowing from the regulator nipple. Is my regulator OK?

BUMP - can anybody tell me if my symptoms indicate a failed regulator?

I know this is an old thread, but i'm having the same issues. Car runs fine, but CEL is on. I have had this car for a few months and the previous owner just put a brand new MAF a couple of weeks before selling it to me. I have cleaned the MAF with the CRC MAF Cleaner, but CEL came on next day, so I don't think it is the MAF. What could it be?

What car? Have you read the fault codes?

I have a 1997 E320. The only code that I got from my neighbors OBDII scanner was P0170, same code the original post is about. The weather was a lot colder here in South Dakota, and the code showed right after it start getting a little warmer, but I highly doubt is temperature related.

bump :(

Did you expect an answer within the hour????????????????

Check the vac hose port on the fuel pressure regulator for gas evidence.

Sorry, I was a little impatient. :o Yes, I just checked that, and I can't detect any gasoline. I couldn't find any vaccuum leaks. Too bad there is no dealer or indies close to where I live. What do you think I should do next? Maybe change the pre-cat O2 sensor?

This P0170 code is driving me crazy. Anyone here encountered the same problem?

From where did the PO source the MAF? The reason I ask is that quality varies greatly. I first bought a cheapie off eBay, and it failed within 2 weeks. The seller graciously allowed an exchange, but the exchanged part failed within a month. I finally broke down and paid $250 from FastLane and haven't had any issues since. I was getting the CEL with the cheap eBay MAFs. Do you have the ability to swap MAF with a known good one?

I haven't swapped MAFs yet, but the one I have it's not even 1 year old. From the receipts the PO gave me, he got it from a Mercedes Benz dealer in Chicago, where actually his son worked, so it is a genuine Mercedes part. Do you think a new MAF will get rid of the code?

There's no way to be 100% positive without having adaptation values read. This will cost you some money at a dealer or competent indy. You can either pay them or spend the money on a new MAF - it's a gamble. As I posted earlier, I took the gamble and it paid off. Besides, I figured even if the suspect MAF was actually good, I could throw it in the trunk and use it as a spare in the event of a breakdown (the car won't run without a MAF). In my experience these cars go through MAFs every couple years anyway; no harm in having an extra one on hand.

Is there any way you can "warranty" that MAF through the dealer since you still have the receipt? I'm from Chicago - which dealer was it?

One thing to keep in mind is that even a brand new MAF can fail if the air cleaner box isn't vacuumed and wiped out, and if a new air filter is not used. If the PO installed the MAF without taking these precautions then it could be toast.

I don't remember off top of my head which dealer it was, I have to look at the receipts, but I remember for sure it is in Chicago. I will just go ahead and buy a new MAF from Fastlane then, didn't know these things are so fragile. Hopefully that's the answer. Thank you for your assistance.