More Surge/Hesitation Diagnosis-2001 S60 T5

[BobbyC]

I've posted here before looking for a solution, but so far no go.

The car (2001 S60 T5, 105k mi) hesitates and surges mostly between 1200rpm and 2200rpm (at least it's most noticible there) under slight load.

Idle is rock steady, and under hard acceleration, the car is perfect (no missing, surging-it just flat goes).

Starting off from idle, the car feels like the throttle is being moved up/down and the engine rpm varies. If cruising at moderate speed 25-45mph, or if you try to maintain speed on an uphill grade (both require slightly added throttle), the rpm bounces up and down (say 1600-1750) as the car accelerates or maintains speed (this is with the torque converter not locked up, naturally). If the TC is locked, the car feels like you are driving into gusty headwinds as you can feel the car accelerate and decelerate slightly.

I've had the car to the dealer (the ETM is still under warranty) and after performing a fuel pump recall (replacement) the car did NOT surge for about 50 miles (just enough for then to drive it around a lot, and for me to get it home again). They recorded no codes, and they said "Passing throttle test at this time," which I take to be the throttle-tracking test.

The Tech said they generally do not troubleshoot cars that don't have MIL or other codes set, but suggested new coil packs, plugs, and a new MAF might cure the problem.

I have replaced all coils and plugs, and also the MAF, and unfortunately the car STILL does the same thing.

Another way to describe it would be to say it feels like you're towing another car behind with a rope, so when the slack takes up, you feel hesitation and restraint, then a half second later, the car shoots ahead slightly. As long as the throttle is advanced, the condition continues.

If I put the car in gear, and hold the brake, and advance the throttle to below TC stall speed (about 1600rpm) the rpm also exhibits this 150 rpm variation.

I put the car on a scanner capable of reading "live data," and it confirms that the rpm, mass air flow, and the O2 all vary as the surge/hesitation occur. The O2 voltage jumps from around 0.1v to 0.7v almost instantaneously, which seems a wide range in only a second or so to me. The Intake air temp on the scanner was correct, so I figure it was OK.

The car is otherwise flawless, giving 25mpg, and I have run good FI cleaner though it on 2 occasions with no effect.

I am not adverse to buying a XeModeX ETM if I were sure it would cure my problem, but having already spend on new coils and the MAF, I hesitate to throw another $600 into the car unless I am pretty darned sure the ETM is the problem.

The Volvo tech said it it WERE the ETM, the car's computer should throw SOME kind of code with the symptom I describe (misfire, fuel trim, something), which of course, it doesn't.

Any last thoughts before this drives me nuts?

Bob

[priapism]

It could just be a dirty ETM. Cleaning it is free, though it takes a couple hours.

[blackpete]

This sounds almost exactly like my problem--not the typical shaky idle symptom. Did you ever find a solution? Did you replace the throttle module? Just clean it? Mine's a v70, but I assume the throttle mod. is probably similar.

[joncott63]

I'm here a year later with exactly the same slow acceleration surge you describe. Recent purchase of an 2001 S80T6 which I've been getting back in shape and love! I'm thinking it's the airflow sensor but haven't cleaned it yet. Did either of you get anywhere on that? I figure it's not electronic or it'd record an error. I did replace a coil early on (as well as rebuild a drive shaft, replace the exhaust, brakes, etc).