850 Turbo won't idle
 

Replaced: Distributor Cap and Rotor/Plugs/Plug Wires/Coil

My daughter recently bought a 1996 850 Turbo with 165k miles. She drove it 900 miles from Oregon to Montana and it performed flawlessly. When she got home she was impressing her friends by putting it in sport mode and accelerating hard. After accelerating it stalled and would restart but wouldn't idle. It will run fine at anything but idle, but as soon as the rpm is near or under 1k it stumbles and will die. The check engine light eventually came on. The codes were P1301, P0300, P0304, P0305.

We replaced the distributor cap and rotor (generic import brand) and ordered plug wires and spark plugs (Bougicord (sp) + Bosch). It ran great after the distributor cap replacement, but then stumbled again after testing it under hard acceleration. When the wires arrived we replaced the wires and plugs. Plugs were well worn, the center electrode on all of the plugs was barely there. Again it ran great but did the same thing under hard acceleration. We replaced the coil (generic import brand) which had no effect on the symptoms.

So now the check engine light is on and it won't idle but will run and accelerate fine if you keep it above 1k RPM.

Any suggestions on what to try next?

find out what the check engine code(s) are first. The P030x codes are all misfire codes (the last digit being the cylinder number, 0 being non specific or random). Misfires can be caused by spark or fuel metering. Idling issues can be a list of things - dirty or failing idle air valve, dirty throttle body, intake air leaks, dirty MAF etc. If your ignition is new - ie coil, cap, rotor, wires, plugs, then I'd start making sure the fuel metering is good by looking for vacuum leaks and clean the intake path. Also you may want to pull out the plugs to make sure they are properly gapped (.028") and are the right part number (OEMs or a simple copper core like Bosch FR7DCs). If you choose to clean the MAF, use a product like CRC MAF cleaner - not harsher generic carb cleaners.

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I should have been more clear. I know what the the codes are and that's what lead me to replace the distributor, plugs, and wires. The misfires are the idling problem. After thinking more about it, the problem reappears after hard acceleration which means the crankcase pressure would be higher with the turbo (I'm guessing) and may be coming out of the front (?) cam seal and fouling the rotor and distributor. As soon as it warms up, we will pull the distributor again and check for an oil leak or condensation. I'll let you know how it goes.

not sure I follow. So say you suspect a clogged PCV system (been there with my 850T). You can do the simple rubber glove test on the oil fill port to see if it inflates. Yes that can push oil out of the cam seals. The cam seals on the 850s can also walk out on their own so you can remove the air box and the cam position sensor to have a look at the rear cam seals and see if they are leaking and note if they are out of place. you'd also want to pop off the timing belt cover to make sure there's no leaks on the front cam seals behind the timing gears. With the air box out of the way its pretty easy to inspect the rotor/cap etc but I've never seen a cam seal leak do anything but drip.
With that said, with all the new parts in the ignition, that should be fine (unless something rare happens like a cracked distributor cap) so I'd move on to checking for intake air leaks as the cause for the rough idle. The vacuum tree under the throttle return cap is a common fault area. Turbos can also have issues with the air tubing from the turbo to the intake (including the intercooler) which can leak air when on boost so you may be due for a smoke test or a cleaning of the intake parts. Last thing to check would be fuel pressure. The 850s fuel pumps often die a slow death so you should check pressure at the rail as well. RobertDIY has posted some excellent vids on Youtube that cover all the common problem areas.

That is a common problem but I have never seen it persist. On my cars it’s just a total shutdown for 2 seconds and then it runs. If the distributor is full of oil then yes, fix that. Simple and easy.

the apparent persistence of the problem might be an illusion. That would explain a lot. We can’t let ourselves consider that you just have to randomly replace something every time you Accelerate hard.

Idling is really easy on the ignition system. However, it’s tough on air metering. Running under pressure tends to create air leaks but if that was the original problem, you evidently fixed it without meaning to or it fixed itself twice.