2001 V70 Intermittent Stumbling at Hwy Speeds - ETM?

englemancr · Post by **englemancr** » 06 Oct 2014, 13:46

I have a 2001 Volvo V70 2.4Turbo with 105,000 miles.

At acceleration from a stop, I occasionally get a momentary hesitation while accelerating.
At highway speeds, It stumbles and bucks intermittently. It seems certain speed/rpm combinations really set it off. Mostly around 50mph and around 2000rpm. It has never given a code either on the dash or via an OBD2 reader.

First thing I did was replace all the spark plugs with original part number plugs from ipd. No change.
Next, I replaced 3 of the 5 ignition coils and rotated them through all the cylinders. No change.
Yesterday, I bought a new (remanufactured) MAF sensor from Autozone. No change.

I have a wifi OBD2 scanner and Dashcommand for iphone to get real time sensor data. I just got back from a drive on the highway and I noticed a couple things. I set the cruise control to 50mph on the the most straight and level piece of road I could find (about 10 miles). Engine was at a consistent 1730ish RPM.

When the engine was running smoothly, I was logging about 23% Throttle position, -12 inches of Hg on vacuum, and about 3.00 lbs/min on the MAF sensor. However, if I were to accelerate up to 52mph using cruise control (foot off the throttle) then back to 50, it would start it's bucking and jumping. Throttle position would vary from 13% to 30% and vacuum would vary between +10 to -26 inHg. Everything else remains the same. It happens with or without cruise control.

Before I spend $500 on a XemodeX ETM, would anyone have any suggestions that I might try? I don't have the idle hunting symptoms like many of the ETM problems I have read about. Can a vacuum leak cause the problems I'm having? Are there common points of failure in the vacuum system? I don't know very much about this car. Are failing fuel pumps an issue with these?

Thanks for any advice.
- Chris

ttrikalin · Post by **ttrikalin** » 08 Oct 2014, 04:04

What about checking for a tear in the bellows after the maf sensor?
that would mess the air fuel trim on acceleration because there is air going in without the computer logging it

Have heard that from someone but cannot remember who...

Will go hide under the table now.

englemancr · Post by **englemancr** » 08 Oct 2014, 04:21

I haven't thought about that but it sounds reasonable. I will definitely check it. I've already spent a lot on on things that didn't fix my problem. It would be nice if it were something as simple as that.

I did another test drive yesterday while watching the car's sensor data. Again, at a constant speed and rpm the vacuum readings would suddenly change from around -14 in/hg to around -3 and the throttle position would drop from about 23-24% to 14%. They seem to be related but I can't determine if decrease in throttle position is following the vacuum or vice versa. Perhaps and air leak is causing both of those changes. Thanks again!

draser · Post by **draser** » 09 Oct 2014, 07:11

Can you look at the dinamic fuel pressure with that reader?

englemancr · Post by **englemancr** » 12 Oct 2014, 09:24

I get a N/A when I try to read fuel pressure, however I get a rock-steady fuel flow of about 1.5 gal/hr reading while driving at a steady speed, even when the engine is stumbling.

I went through the vacuum system today and replaced any factory hose clamps that seemed loose with the old screwdriver hose clamps. No change.

I replaced the MAF sensor with a third, used one. Again, no change.

I also printed the ETM flowchart diagram from the XemodeX website. My situation applies nowhere on that sheet, so that's why I am reluctant to purchase one. I have also attempted to call XemodeX at least 4 times last week. A customer service rep said they would have someone from tech support call me, they never did.

If I drive 65mph, the throttle position stays steady at about 25% and the engine is smooth as silk. The engine jerking only happens when I transition through, or remain steady at, a throttle position range of about 18-23% throttle position, regardless of speed or transmission gear.

Would this be a good candidate for a Saucer TPS replacement? What is the difference between just replacing the TPS with a contactless and ordering a whole new XemodeX ETM? I'm really trying to avoid spending money on something like that only to find my problem was elsewhere.

Thanks again, Chris

englemancr · Post by **englemancr** » 17 Oct 2014, 18:42

Update. Problem solved.

I took my car to an independent Volvo mechanic on Wed and had an ETM sweep test done. The maximum difference was 76 degrees. The mechanic said he had never seen an ETM that bad.

Called XemodeX on Thursday at 11am. Had a new ETM at my door today, Friday, at 8 am. It took about an hour and a half to install and the car runs perfectly. It solved all my issues.

Hope this helps someone in a similar situation - Chris.