1999 S70 RPM Fluctuation and deep vibration.

brettbo · Post by **brettbo** » 25 Jun 2014, 07:00

Recently my 99 S70 has been having a rough thud and engine vibration whenever I am idle at a light or when I put the car in reverse. The RPM is also fluctuating from 400-1200 when this happens. Also when taking off from a light there is a bit of a vibration from under the hood and a deep thud sound. I looked under the hood with the car running and the top motor mount was shot and the engine was moving around about an inch and a half back and forth, so with my initial thought that it was the top motor mount I replaced that. Took a drive and the issue is still going on. Another thought is that it may be an ignition coil that has gone out but the weird sound and vibration when putting it in reverse has me thinking worst case scenario like a transmission issue. Any ideas on what this could be?

Post by **mecheng** » 25 Jun 2014, 07:50

Clean your idle air control valve

Post by **rmmagow** » 25 Jun 2014, 08:26

Sounds like the lower motor mount near the crank. Check through here, there's pictures and instructions. Not a biggie by any means to fix.

Post by **misha** » 25 Jun 2014, 17:36

brettbo wrote:...The RPM is also fluctuating from 400-1200 when this happens...

'99 have Denso engine menagement and with that idle fluctuation you have...it could be two things.The dreaded ETM module failure or just a Maf sensor failure.

I bet that it is ETM.

Read the codes & post them for a precise diagnose.

instarx · Post by **instarx** » 26 Jun 2014, 03:40

misha wrote:
brettbo wrote:...The RPM is also fluctuating from 400-1200 when this happens...
'99 have Denso engine menagement and with that idle fluctuation you have...it could be two things.The dreaded ETM module failure or just a Maf sensor failure.

I bet that it is ETM.

Read the codes & post them for a precise diagnose.

Symptoms sound like it could a combination of two things. The thud being the motor mount, and the wondering idle being the MAF or ETM. I've fixed the ETM and replaced the motor mount on my 2000 and neither is a huge job. An hour for the motor mount and three hours to take out the ETM, clean it, and re-install.

There are good instructions here for the motor mount, and XmodeX has a great instructional video on removing the ETM. Of course XmodeX wants you to buy their expensive (but excellent) ETM, but mine only needed cleaning.

Post by **abscate** » 26 Jun 2014, 04:09

If you sit at idle in park or neutral, is the idle normal ?

brettbo · Post by **brettbo** » 26 Jun 2014, 07:39

It seemed to be OK in park or neutral, I will have to check again. I am not getting any engine codes. I won't be near the car until tomorrow or Saturday so I will try cleaning the ETM. One thing I would add is it almost sounds like metal clinking somewhere during the vibration.

Post by **E Showell** » 26 Jun 2014, 15:11

I have had the exact same condition in my '98 5 speed, non-turbo. It was not cured by engine replacement. The idle drop is a bit less pronounced (only a few hundred rpm) and the vibration is there as well. On mine the vibration is not linked to a motor mount issue since the problem persisted even after all of my motor mounts were replaced. JRL said he had a car with the same issue at one point and it nearly drove him crazy. I've lived with it for years and just learned to ignore it. I have also changed the MAF on my car and it had no effect on the issue. Given that the '98 lacks the problematic ETM, I'd be willing to venture that it is not the ETM either. The issue generates no codes on my car, so there would be none to post. I've basically given up trying to diagnose/fix it.

Post by **ThinAir** » 26 Jun 2014, 17:18

Hey E,

I have done the same. A while back I replaced the ETM, MAF, Turbo control valve, various hoses, Evap purge valve-basically a lot of stuff, but my idle will still dip from 800 to around 300-400 every now and again. I have no idea why and have just learned to live with it.

J

Post by **JimBee** » 26 Jun 2014, 20:43

My 93 850 5 speed has an occasional rpm fall-off, too, when I come to a stop and begin to idle. Sometimes I wonder if it's going to stall, but it never does. There aren't any sounds or intense vibrations associated with that, just a slight shuddering from the low rpm's.