1996 850 turbo rough idle and stutter

Post by **steve850** » 31 May 2014, 22:27

Hey all. Spent hours reading the other posts on this, and seen pretty much the same stuff everywhere (which I think I've already covered) so I'll outline what I've done so far...

Car had a hesitation /stalling problem last year, but was planning major work anyway because it was blowing oil through the turbo like crazy. Pulled the head, did the valve seals. Lapped valves, generally checked everything out. Seafoamed the rings while the head was off. New head gasket, head bolts, timing belt, water pump, plugs, wires, cap, rotor. Swapped my blown 15g turbo for a 16t with a new down pipe. Changed all the intercooler hoses. PVC was already done but cleaned it all out anyway, it still has a little blow by so I "upgraded" the ptc line with a bigger hose. Cleaned the injectors (off car) Cleaned the throttle body (off car)

All back together and the hesitation / rough idle is still there. It starts, idles for about 10 seconds then starts to get rough and has poor throttle response. If you rev it, it is not 100% smooth. If you let it idle, it gets rougher until it eventually stalls. Cleaned the MAF, and if I unplug it with the car running, it gets worse or dies. Same for the Idle Control Valve. And the TPS. Checked all the vacuum hoses and the vacuum tree.

And there are no codes ( other than a TPS code from having disconnected it) cleared that code and no new ones.

Compression is a little low, varies between 160 and 155 across all but no huge variations.

Anything I've missed? This one is really stumping me

Thanks !!

S

Post by **rspi** » 01 Jun 2014, 07:31

I would replace the MAF.

Post by **erikv11** » 01 Jun 2014, 08:23

Agreed, get a junkyard (Bosch) MAF and pop it in there.

Post by **steve850** » 12 Jun 2014, 13:41

Swapped out the MAF for à Knowles good Bosch, put in some fresh gas, not much change - will not idle. Next up is the IAC valve

Post by **Ben850** » 12 Jun 2014, 17:03

I have said it before, and been shot down by other members.
The reason I have a 1996 Turbo Wagon for the original purchase price of $650. is for the fact of the front O2 sensor not letting it idle.

I had only figured it out after swapping MAF, TPS, ICV, etc...

I had found a genuine Bosch front and rear O2 sensor in a salvage car that were new.

Either buy a new Bosch front O2, or find a salvage piece for diagnostics.

It is the very reason I have this car.

https://www.matthewsvolvosite.com/forums ... 35&t=56550

https://www.matthewsvolvosite.com/forums ... 35&t=56550

Post by **abscate** » 12 Jun 2014, 17:54

You should be able to check the O2 sensor with a tool that shows the duty cycle and voltage before throwing parts, but it sure seems like it is narrowed to the sensor

Post by **steve850** » 12 Jun 2014, 20:06

I'll see if my scan tool will give me O2 sensor data... And i'll recheck the sensor. Seems to me I swapped it out when i changed the downpipe with the new turbo, but that was last summer, and my memory aint what it once was

Thnx for the suggestion !

Post by **steve850** » 12 Jun 2014, 21:56

Another little thing. Having read that on higher mileage cars the hose between the intake and the PTC is often too small, I replaced with a larger rubber hose. I have noticed that when you open the throttle a bit aggressively, the hose collapses. Should I plumb in some copper or not worry? Also, Is this amount of vacuum normal at this point in the PCV.

Tnx

Post by **steve850** » 19 Jul 2014, 14:30

Well - had some time to work on the Platinum some more.
Took Ben's and others suggestion and changed the O2 sensor for a new Bosch - better, but still not good.
The problem is narrowed to: starts and revs to about 2000 when cold, then settles to a fairly even idle and then dies. Found a slight crack in the vaccuum line coming off the end of the manifold going to the PTC, but the car behaves exactly the same with this line wide open anyway.

Once warmed up a bit, will not start. Almost starts, but not quite. Floor it and it will catch, but just.

To sum up
Compression 165 lbs cold and dry across the board, which is up from 150 before I did the timing belt and valve seals, etc. Not bad for a 250k mile car with original rings
Swapped out MAF and Idle control valve
Changed O2 sensor
New plugs, wires, cap and rotor (bougiecord wires)
New fuel filter
Injector's cleaned (done off car with pressurized cleaner and some voltage to run it through)
Checked and rechecked vacuum hoses.

Tests show that vacuum is a little below "normal" on my gauge, but that could be because it is a turbo.

Plugs are black, which would indicate either rich or not enough spark, so I'll leaning towards a bad coil at this point, but I've never hear of a coil going bad on these cars

Anyone else have any thoughts?

Thanks

Steve i

Post by **abscate** » 20 Jul 2014, 07:08

We just had a similar bad coil that showed a spark, but a new coil fixed the no-start condition completely. If time>money I would try a brand new OEM coil