1995 850 2.0 20V Idle and running problems

frootmig · Post by **frootmig** » 23 Aug 2008, 07:04

Hello,

I have a 1995 Volvo 850 2.0 20V Automatic, the car appears to be between a 95 and 96 model as it has an OBDII connector, but I had to make a little LED and switch combo to read the usual flash codes, found the info on this excellent site.

The car has recently had a full service, new plugs, air filter, oil etc...

The problem started while we were on holiday with the engine intermittantly cutting out, I called the RAC out, after looking at the codes (it was 1-2-1, showing a MAF error) we unplugged the MAF sensor and the engine ran without any problem, other than poor idle (I put this down to the MAF being unplugged), we drove the car home (Over 270 miles) without any recurrence of the cutting out problem, the fule consumption was almost the same as it had been before the problem.

When I got home I ordered a new MAF sensor (Not a Bosh original) and fitted it when it arrived.
I cleared the codes and started the engine, the engine started well and appeared to idle quite well, I then moved the car into D the engine almost stalled. I thought it may be the PND switch so I moved the shifter back and forth several times but it did not help.
Next I tried to rev the engine, firstly it hesitates on initial acceleration, but if I open the throttle wide open the revs will hunt with the revs going up to about 4000 and then cutting out and dropping to about 3000, if I close the throttle a bit the revs will stabilise, if I open the throttle slowly the revs will happily go past 4000. I have looked at the vacuum hoses and found one with the rubber connector perrished, I have replaced that, but the problem still exists. I thought it was originally the new MAF that was faulty so I sent it back, but the replacement gives exactly the same problem.

I have removed the IAC valve and used the diganostic tests built into the ECU to test it, with the IAC closed it is still allowing some air to pass when I blow through it, should the IAC valve seal completely when closed?

If I unplug the MAF the engine revs freely to 7000 rpm without any problems and drives quite well (lacking a bit of performance) so I think it rule out any problems with the ignition and fuel systems.

I think the problem with the revs hunting when the throttle is quite wide open must be due to a leak in the intake system, but I am not sure where to look now.

Has any body got any ideas where I can look next, I am running out of ideas, please help

Frootmig....

Post by **MadeInJapan** » 23 Aug 2008, 07:50

Unplugging the MAF causes the car to run in a limp mode, which allows decent running no matter what kind of air leaks you have. The IAC should be tight when in the off position (I believe). I had similar symptoms once and it ended up being a crack in my intercooler (I have a turbo- do you?). Anyway, check all of your hoses AGAIN, and take the plastic engine covering from under the car (2 10mm size sockets on each side) off that covers also the radiator/intercooler and see if the 90degree hose at the bottom has come loose or there is a hole in it as well as cracks along the underside of the intercooler- you have air leakage somewhere, whether it's the IAC or something else.

frootmig · Post by **frootmig** » 23 Aug 2008, 08:01

Hi Madeinjapan,

Thanks for the reply, I do not have a turbo, but I will check all of my hoses. I agree I have an air leak somewhere, there are about 5 different vacuum hoses on the inlet manifold, I am going to have to trace them all and check them.

Thanks for the reply, I will let you you know if I find the problem.....

frootmig · Post by **frootmig** » 04 Sep 2008, 06:20

Just to keep you informed,

I have cleaned out the PCV system (It was blocked solid), I have replaced all of the vacuum hose connectors (a lot of them were perished), cleaned the throttle body and even replced the o-ring on the vacuum tree (this had gone hard and was not sealing).

I have checked all of the vacuum hoses for leaks and they all appear to be ok, I have checked the fuel pressure regulator diaphram and the v-vis diaphram, all ok.

I have removed the ECU and checked it for bad solder joints (i repaired my ABS controller a while ago and that was due to bad solder joints). no problems found.

I still get the same symptoms when I plug in the MAF sensor and clear the codes, the only code that is set is the 1-2-1 code for the faulty or missing MAF signal.

Has any body had problems with the throttle body or inlet manifold gaskets causing problems, because I am down to either that or faulty wiring between the MAF and the ECU or a faulty ECU

Any comments would be greatly appreciated.

Frootmig

Post by **vegasjetskier** » 04 Sep 2008, 07:54

Maybe your new MAF is bad?

frootmig · Post by **frootmig** » 04 Sep 2008, 08:14

Hi,

I thought that when I got the first MAF and it gave the same problem, this is the second MAF that has given the same problem, I suppose it could be a bad batch, I will have to see if I can get a different on to try..

thanks for the reply....

Post by **vegasjetskier** » 04 Sep 2008, 08:27

Can you get the OEM type to try?

Post by **vegasjetskier** » 05 Sep 2008, 18:37

Check out this page: http://volvospeed.com/Repair/maf_secure.php

frootmig · Post by **frootmig** » 06 Sep 2008, 05:57

Yet abother update...

I have checked all of the wiring between the MAF and the ECU, all the connections show a resistance of approx 0.2 ohms , this is the value I get when I short the 2 meter leads together, so it must be about 0 ohms.

I have measured the voltage on pin4 of the MAF when the engine is idling and this is about 0.8v, if I disconnect the inlet side of the IAC this drops to about 0.26v so the MAf is definitely reading the air flow.
When I open the throttle the pin4 voltage increases as the throtle opens, but this appears to reach a maximum of 3.2v and goes no further, but it reaches this voltage when the throttle is only about 25% open (this is a guess) once you open the throttle beyond this point the engine dies until the revs go bleow a certain point and then the cycle starts again.

Can anybody tell me what is the normal range of volatges from the MAF from idle upwards, I am still wondering about the MAF I bought and I am running out of things to check.

Just one other thing, I have been going through the Trouble Shooting with codes document from this site and one of the checks is to measure from pin1 of the MAF to ground, it says that this should measure 0ohms, but I have checked this and it shows as an open circuit, the connection to the ECU pin A12 is ok I have measured this but I am not sure if this test is correct for the ECU that I have (LH 3.2), has anybody else done this test before?

Any Comments as ever would be much appreciated...

Frootmig....

frootmig · Post by **frootmig** » 07 Sep 2008, 10:37

Hi, me again,

While looking around for MAF info I found this datasheet for Bosch MAF sensors, http://modshack.info/images/sensors_airmass.pdf hope this may be of some use to somebody, is there any way to upload a copy of it on the site?

Frootmig...