V70t poor acceleration hesitation warm revs in steps 2001

Volvo12345 · Post by **Volvo12345** » 07 Jan 2011, 10:37

All,

I've a 2001 V70t that has had its ETM replaced however, it has subsequently developed the following symptoms - when cold will accelerate smoothly, when warm will accelerate very poorly and will not redline. Driving gently all is well, driving hard the car stumbles and accelerates. Very occasionally the revs. will drop when you back off, but the tickover is even. Coming of cruise control the car will stumble. Very occasionally when setting off from cold the car will move very slowly for a few seconds then suddenly recover and drive fine. In neutral it will not rev smoothly and the engine accelerates in steps.

Four mechanics have looked at it and it has no vacuum leaks. It runs slightly below temperature (broken thermostat) but even when driven in town and so at normal temperature it still stumbles. The CEL is on and a scanner reports 'engine running lean'. It also feels a little low on power once warm.

The Volvo garage that changed the ETM three months ago are refusing to even look at the car without an hourly charge and my four independents have not found a problem. The MAF was suspected, was changed but it failed to start the next day and so was returned to the original. I can clear the CEL but it returns quickly.

Car has 80k and an ok service history. Uncertain when the plugs were changed but the mechanics commented they look fine.

Any ideas? Thanks for any advice, it has had lots of garages stumped and the main dealer is shockingly poor, offering the comment that 2001 cars are dogs. thanks!

skeeter123 · Post by **skeeter123** » 07 Jan 2011, 12:55

If you KNOW the thermostat is broke, replace it. Also, check the ECT to make sure its reporting temp correctly in range. Bad readings from the ECT can affect the fuel mixture.
Hope this helps.

Post by **jimmy57** » 08 Jan 2011, 21:39

The things that come to mind are leaks in hose from MAF sensor to turbo inlet, faulty MAF sensor, Faulty turbo control valve.
The Thermostat being bad should be fixed but if they used scanner and coolant temp reached 95 or a little above then it would not cause symptoms once warmed up.
Cars in the UK probably are not required to set codes for the same problems as North American market models and you did mention any codes reported by the workshops.
A crack in the accordioned sections of air hose to turbo will cause leanness as MAF is not measuring all the air entering engine and will not compute correct fuel quantity for injection.
A faulty MAF can do the same thing and the MAF has to be a great deal out of normal range before codes set.
Turbo control valve will cause boost level cycling (steps in acceleration) but I have never seen hesitation from one of those that is faulty.

Post by **E170_Driver** » 10 Jan 2011, 04:44

Also check the MAP (not MAF) sensor...it can cause trouble on turbo models.

Jan

Volvo12345 · Post by **Volvo12345** » 06 Feb 2011, 06:04

Hello All

thanks for your suggestions. I've had the induction system checked and no one can find any leaks. I'v replaced the MAF and it does solve the jerky acceleration - car now seems back to normal power. So thanks for that advice. HOWEVER, it does not tickover well and although it accelerates smoothly, will stall at tickover and revs drop at lights before recovering and staying steady at around 800rpm. If I drive with the MAF unplugged I get more constant power and rough tickover but the revs do not drop in the same way - they fluctuate like mad but then v. quickly settle to 900rpm. It feels better with the MAF unplugged. WHY?! Is there another sensor that is disabled if the MAF is unplugged that defaults to a standard setting?

I get four error codes only if the MAF is unplugged P0121 TP sensor circuit insufficient activity, P1132 powertrain Ho2s circuit low variance bank 2 sensor 1, P1171 and P0102 which are missing MAF and running lean.

I don't understand why running without the MAF sensor is better and why (two now) new MAF sensor make no difference... There also seems to be some confusion as to if the car has a MAP sensor? Also, I'm not sure how to check the PCV system.

thanks so much for your help and I can recommend Proscan and an Ebay Elm reader...

Post by **E170_Driver** » 10 Feb 2011, 00:54

This is the MAP sensor in the very front of your engine compartment...

...and yes you certainly ought to have one.

Jan