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Is the intake air temperature built into the MAF? I can't find a replacement part for it.
I'm using a Blue Driver scan tool and it's showing my intake temperature at a minimum 84°. It went over 100° in park with the engine at normal operating temperature. It's currently 45° ambient. I drove the car to make sure it wasn't picking up residual engine temperature warming up the airbox
Question 2-- my safety/tamper Torx T25H will not fit on the MAF fasteners? is it an OEM tool? The pin in the center looks larger than a hole in my bit.
I'm having a rough idle (vibration) in gear with the brake on. RPM under 600. I was getting an EGR valve code, replaced it and issue got a little worse. All of my hoses are tight. I replaced the manifold pressure sensor and used spray cleaner on the MAF and it seemed to improve for a day and now it's happening again. I have K&N filters. I cleaned them and did not re-oil them in the event the oil was carrying through to the MAF.
Motor mounts, transmission mount, coils, plugs and I just repaired a rough idle that was caused by 1 plug wire that had a slightly higher resistance than the others. I don’t see either high iat or faulty iat sensor causing rough idle in drive.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Miwettig
I'm having a rough idle (vibration) in gear with the brake on. RPM under 600. I was getting an EGR valve code, replaced it and issue got a little worse. All of my hoses are tight. I replaced the manifold pressure sensor and used spray cleaner on the MAF and it seemed to improve for a day and now it's happening again. I have K&N filters. I cleaned them and did not re-oil them in the event the oil was carrying through to the MAF.
Get rid of the K&N and go with stock. Do all the things that @cdk4219 listed. Clean the MAF again. You may need a new one.
I replace the MAF, installed stock air filters. RPM still drop below 600 in gear stopped with brake applied, vibrates until RPM gets above 600. Neutral or Park, RPM average of 650… Zero vibrations. It seems as though the air pump is kicking on for a few seconds when I come to a stop, and the vibrations at its worst, then the pump shuts off in the RPMs go up?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Miwettig
I replace the MAF, installed stock air filters. RPM still drop below 600 in gear stopped with brake applied, vibrates until RPM gets above 600. Neutral or Park, RPM average of 650… Zero vibrations. It seems as though the air pump is kicking on for a few seconds when I come to a stop, and the vibrations at its worst, then the pump shuts off in the RPMs go up?
The air pump should ONLY be activated on a cold start. The purpose is to inject additional air into the exhaust stream to heat the catalytic converters quickly. Once the cats are at temperature, the air pump should stay off.
If you are in Park or Neutral when stopped and no brake applied, does the RPMs drop below 650? Everything in your car is pretty much controlled electrically, including the brakes. If there is an electrical load causing the alternator work harder, that could be causing the engine speed to slow down.
Do you have any DTCs now? Have you cleared them since making your changes?
RPM does not drop below 650 in neutral or park without the brake applied. If I apply the break in park or neutral, it will drop slightly for a second then come back up. I have noticed anytime there is an increase electrical load the RPMs drop. The alternator was going to be my next question. I do not have any codes. What would cause the air pump to come on after the engine is up to temperature? What tests can I do to the alternator other than measuring the output voltage? 130,000 miles
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Grasping at straws here, but it could be the alternator. I think you can get a battery/alternator checker on Amazon for cheap. It seems that any electrical load brings down the rpms.
How do you know it's the secondary air injection pump that is activating and not the electric fan? Try turning off the A/C and see if the symptoms are the same.
I took the car to Harbor Freight to buy a battery/alternator tester with my scan tool running and coming to a stop the RPM's dropped as previously described and the message in Fuel System Status window changed. I attached 2 screenshots, one is normal the other shows.... open loop - power enrichment - deceleration enleanment - cylinder deactivation. It cleared within a few seconds then at the next intersection, I got the same message. The rest of the day driving I got the same RPM drop and vibration below 600 when coming to a stop but did not see the fuel system status message again. I don't know how fast the refresh rate is on this app, maybe it doesn't catch it each time.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
How long had you been driving? Coolant temp should normally be in the 198°-212°F range, depending on your speed. 162° seems low if you've been driving more than 5 minutes. Right now, the temps are mild (~50°F) in Maryland. Maybe a stuck thermostat? Or a big vacuum leak? I would recommend a smoke test. I know you don't want to keep throwing money at this, but these tools will last you a long time. I used my smoke machine once or twice, so maybe not cost effective...until you need it. This one has good ratings and is $77 after the $10 coupon.
Will any of these issues cause the vibration when the RPMs go below 600. Rpm 610 and above… Purrs like a kitten. I started this thread about intake air temperature but it's all looking to find the cause of this vibration.
This time of year, they put more ethanol in the gasoline, supposedly to pollute less? I dunno. But that may be part of the cause of a ruff idle. Also, I was buying gas (always the Premium/highest octane) at Kroger/Fred Meyer stores and never had an issue but tried Costco gasoline and found a rough idle ensued. Maybe there's water in their tanks? Maybe there's nothing wrong with the car.
I had the car out again today for an extended period of time. It took several stops, then restarts before the coolant temperature got to 174. The vibration was significantly less when the RPMs dropped to idle. I'm going to install new thermostat and change the fuel filter.
12-14-2023, 04:50 PM
