engine surge

jackteet · Post by **jackteet** » 17 May 2018, 21:10

Hi, I have a 1998 V70, 2.5, 20v petrol non turbo.It has covered 140,000 miles. I always drive with gearbox in "economy".The problem occured for the first time yesterday. I reached 50mph and lifted off the accelerator as usual so the torque converter would lock into 4th gear or overdrive; I am not sure which. The revs were 2,000 but dropped to about 1750.within a second or two the engine revs increased to about 2200 and then back down to 1750.This happened at least a dozen times until I accelerated to about 60mph when the engine surges stopped. The gearbox oil level is full and red in colour.Gear changes are smooth and quiet.Were it a manual box I would compare the surges to a slipping clutch.
For my return journey I switched the gearbox to "sport" mode and everything was fine.
I would very much appreciate your views please.

Post by **erikv11** » 18 May 2018, 08:01

Have you ever changed the transmission fluid? If not I would change it all (takes about 14 liters using the hose from the transmission to the radiator), then every 30k miles or equivalent kms do a drain and fill of the drain pan (3.5 liters).

jackteet · Post by **jackteet** » 18 May 2018, 08:29

Hi ERIKVII, Thanks very much for coming back. My engine and gearbox came from a donor car and were fitted about 1500 miles ago.
The mechanic said he put new gearbox oil in when fitting. Are my current problems usually associated with the oil.The symptoms appear to be gearbox related but would you know if these could be replicated by say an electrical problem; I am thinking ETM. Thanks again for your help; much appreciated. regards jack

Post by **Kara503** » 18 May 2018, 12:41

Jack, if your car is a 98, it doesn't have an ETM- your car should still use a throttle cable so you can rule that out. My first instinct would be that the problem is electrical if you swap to Sport and the issue goes away. If I were in your shoes, I would go about removing the TCU, cleaning all of its contacts really well, and then replacing it. I would wait to do that, though, until some of the more seasoned members of the forum share their opinions

An edit- forgot to mention, you should unhook the transmission end of the wiring harness to clean and reseat it as well.

jackteet · Post by **jackteet** » 18 May 2018, 15:12

Hi Kara503, Thanks very much for that. Most reassuring as I thought I would need another gearbox. I would certainly appreciate all opinions.regards jack

Post by **FLXC90** » 21 May 2018, 23:10

Jackteet, When the "S" is engaged, it may raise line pressure requirements for upshifting. A sticking solenoid sounds more likely the culprit here. I have 240k on my 98 N/A and it does the same thing at 40-50 mph. I would recommend a fluid change first, then evaluation of solenoids, valve body, or clutch pack wear.

Let us know your outcomes.

jackteet · Post by **jackteet** » 22 May 2018, 09:45

Hi FLXC90, many thanks for that. Forgive my ignorance but is there a specific solenoid for the auto box and if so can it be cleaned or is it best to replace it. May I ask what connection the throttle body has to the gear changes. Again apologies for
for my ignorance. thanks again. jack

Post by **FLXC90** » 23 May 2018, 00:50

There are different solenoids to trigger shifting in the automatic transmission, and to lock up the torque converter. There are threads that cover the change, but it is usually a job left to "experts". Solenoids may suffer from contamination buildup in their operating bores, especially in higher mileage or poorly serviced units. Fresh fluid may help in that case. The threads for solenoids are usually tied to the 2001-2002 60/70 series cars as they had a new development 5speed auto that experienced problems in the shift solenoids and valve bodies. For cars with Electronic throttles, the ETM may cause surging that can be confused with the symptoms of a transmission problem. Easy thing to check, look under your hood and see if you have a throttle cable. It should run to the throttle pretty much behind the left edge of the radiator, about 40cm back from the radiator

jackteet · Post by **jackteet** » 23 May 2018, 09:16

Hi FLXC90,Thank you very much for the info.My current engine and gearbox are from a donor car which were fitted about 2,000 miles ago. New g/box oil was put in and that is full and pink. I have a trottle cable.
Should a faulty solenoid show up on the fault codes. The gearbox is very smooth and gear changes are hardly noticeable except the final change at 2,000 rpm. It changes like a machine gun.
The really strange thing is the brake lights switch failed at the same time that the engine surges started, coincidence as I am sure the two cant be linked. From reading your advices I am leaning toward an electrical fault rather than a mechanical g/box problem. The next item on my list is a throttle body clean. Thanks jack.