Engine Hesitation

[jheissle]

I have a 2001 XC70 with 100,000 miles. It idles fine, but seems to hesitate on a light acceleration and also when driving seems to jump like if you suddenly take your foot off the gas when accelerating you get that weight shift in the car. I don't get an misfiring at idle, but if I get the RPMs up to 2,000 in drive with my foot on the break and hold it there, I will see it routinely get this same issue with the engine. No codes are being set. Any suggestions? I have new plugs installed and that didn't fix the problem.

Thanks!

[KYANGC130]

I have a 2001 XC70 with 100,000 miles. It idles fine, but seems to hesitate on a light acceleration and also when driving seems to jump like if you suddenly take your foot off the gas when accelerating you get that weight shift in the car. I don't get an misfiring at idle, but if I get the RPMs up to 2,000 in drive with my foot on the break and hold it there, I will see it routinely get this same issue with the engine. No codes are being set. Any suggestions? I have new plugs installed and that didn't fix the problem.

Thanks!

I was just lurking the forum and saw your post. Here's a message I posted on another forum recently. It may sound familiar.


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



I later took my car to an independent Volvo mechanic and requested an ETM diagnostic sweep test. This test checks the two Throttle Position Sensors within the Electronic Throttle Module. The should read the same, but because they are a flawed design, they tend to wear over time and the two sensors become out of sync. Mine were out of sync with a max differential of 76 degrees. I called Xemodex, ordered a new ETM. It arrived this morning and I installed it in about an hour and a half. The engine now runs perfectly. They're not cheap, $500. But they used a different type of TPS that do not wear and are guaranteed for life. You'll never have to worry again.

Hope this helps. - Chris

[jheissle]

Wow, this is identical to my problem. And I have also tried swapping out an ignition coil and cleaned the MAF sensor with no improvement. Was just about to try a new MAF sensor before I pulled the trigger on the XemodeX ETM, but am guessing that would end up just being another $100 wasted. Thanks for the help. Will let you know if the ETM fixes it.

[JRL]

Try to clean the ETM (throttle body) first
If no help you may need a new one but have the test done first

[jheissle]

Well $550 and 3.5 hours later the problem is fixed. Replaced the ETM with one pre-programmed by XeModex and the car runs like new.