Heartbeating like idling

[allirroz]

what issue could this be?
99 c280. Symptom is , car idles like how our human heart beats . Like a pulse beat, Like idle is hunting on Drive with brakes applied and on Neutral, BUT idle needle is steady . No visual fluctuations at all.
Its not a constant vibration which would seem to lead as an engine mount issue-
Could this pulsating idling also be another engine mount symptom?
Cars runs flawless, No CEL light, other that this pulsating issue.
Any input would be greatly appreciated
Thanks in advance

[hvmercy]

does it buck forward?

I had this symptom on my C230 about 5 years ago. Took it the dealer to be looked at and I forgot what the fix was. Let me dig up the service records and I'll post it.

[jnenad16]

unplug the MAS as see if it changes. if not, thats probably it.

[allirroz]

Originally posted by hvmercy
does it buck forward?

I had this symptom on my C230 about 5 years ago. Took it the dealer to be looked at and I forgot what the fix was. Let me dig up the service records and I'll post it.

Hvmercy. no bucking or jerking at all, appreciate if you could retrieve old service record


Originally posted by jnenad16
unplug the MAS as see if it changes. if not, thats probably it.

Jnenad16- I'll try that.- could very well be the MAS as this was the only one part and I've replaced ( electronically) on the car other than the dreaded recall crankshaft pulley.
If I unplug MAS would it trigger the ck engine to come on?

Thanks much gentlemen!

[OzC36]

hvmercy,

Any luck with the old maintenance records on the bucking problem!

[hvmercy]

Originally posted by OzC36
hvmercy,

Any luck with the old maintenance records on the bucking problem!

sorry, dropped the ball.

I'll dig it up when I get home tonight

[hvmercy]

MAS was replaced.

sorry it took a while to dig up.

[allirroz]

Is there a any difference between after Market MAS and dealer supplied ?
I bought mine from either ( as I don't recall )importec or autohausz? I believe it's a Bosch.
I still have my OE mas, is cleaning a viable option, with- Is it CRC you gurus recommend to spray clean?

HVmercy can you elaborate "bucking" - I may have misunderstood you with your initial symptom inquiry?Also, been busy of late and never had the chance to apply Jenad's process of elimination.
Thanks man!

[OzC36]

Thanks hvmercy!

allirroz,
There can be the world of difference between the OEM and the aftermarket parts. The Bosch type is the OEM and strongly recommended. Whether there is any difference between the Bosch part number sold by Autohaus and the same Bosch part number sold by MB Dealers, I wouldn't think so..? To clean, use CRC circuit-board/switch cleaner...it is not always successful in restoring correct function.

[jnenad16]

to clean the MAS hot wire, use the CRC MAF cleaner, it is specifically designed for that. however, I doubt that will help, as your problem sounds like the circuitry inside the MAS is defective.