98 s70 hard idling/stuttering

[Keshavsmith]

Hey guys. I’ve been driving a 98 S70 T5 for about a year. Everything’s was fine until a couple months ago when I was driving on the highway and the car started stuttering and losing power so I pulled over. I shut it off and then started it again. It would start but not drive but a few feet before dying again. I had it towed to a mechanic(I am a single female and have no experience with working on cars). The mechanic said the computer read engine misfire. He changed the spark plugs and spark plug wires and said it was running well again. I picked it up and it was fine for like 5 minutes before it strarted doing the stuttering thing again, but only when I was at a complete stop(it was fine when
I was in motion). Took it back to
Mechanic twice, he could’ve figure out what was wrong. Found a new mechanic but in the meantime it had occurred to me that it could be a gas issue. You guys will come after me for this, but I’d been putting 87 in it despite being told it needed 93(I had the exact same car prior to this one, color being the only difference, and I put 87 in it and it was fine so I figured it’d be ok and gas is sooo expensive). I mentioned this to the new mechanic. They checked the whole car over, drove it twice, and determined it was the gas issue. I put octane boost and premium in the tank and it stopped the hard idling INSTANTLY. This was two weeks ago and it’s been great ever since. I’ve driven it on a 4 hour road trip and here around the city and no problems until today. On my way to work it started the hard idling again at a stop light. I’m at loss here because these mechanics can’t seem to understand what’s going on and I’ve already spent over 1000$ getting this car looked at and spark plus, etc, replaced.. any ideas? I spoke with a member of this site who’s helped me before and I passed along his ideas to the mechanic but I don’t get the feeling they even listened or checked out the things I mentioned. Any suggestions would be appreciated… in what might be happening
Or how to get mechanics to listen. This is frustrating. Thank you so much!

[scot850]

Assuming the mechanics fitted the correct plugs and gapped them correctly, the wires can be an issue but the old OE Bougicords don't go wrong often unless they are damaged. They don't last forever, but it is uncommon for cables to shut the engine down. Misfires on cylinders yes, but not whole engine. Aftermarket brands of cables are very hit or miss.

For the engine to die there is a list of issues that can cause this behaviour unfortunately. A list which is far from exhaustive are:

1) Fuel pump
2) Fuel pump relay
3) hard starting could be fuel pressure valve
4) MAF
5) Cam/crank sensor

You can also add air/vacuum leaks in pipework.

This is where a code reader comes in helpful, but for 98's many off the shelf don't work.

Not sure if there is anyone in your area that may be able to help?

Neil.

[greg850r]

fuel pressure would be my first check. How old is the fuel filter?

[yanga001]

I would say a decision needs to be made if you want to dive into more DIY and fix your car yourself or trust some run of the mill mechanics.

I know there are good mechanics out there, but normally you need to develop a pretty good relationship with them before they start really listening to the details and ideas your provide them. I would recommend buying an obd2 scanner which can check live data of the car. That way you can pull your own codes and check things such as fuel trims, engine timing, etc.

To me it almost sounds like a vac leak as the car seems to start properly but will intermittently die.

To work on these cars you need the following:
A torque wrench: see if you can get 20ftpds-100ftpds range. That will cover spark plugs, any brake calipers and wheel lugs
A socket set: you only need a few of the metric sizes, i cant rattle them off the top of my head but a 100$ set on sale should do. (8mm,9mm,10mm,12mm,13mm,14mm,16mm,18mm,19mm)
a hammer
a screw driver set

Did he check the distributor cap and rotor. Sometimes they can get a bit contaminated, and can go bad if oil leaks into them.

If it happens again, and you do have a scanner then write down what misfire it occurred on.

One cylinder misfire could point to a bad injector/potential issue on the rotor/cap. Constant multi-cylinder misfires are a bit wider and could point to Mass air flow sensor/Cam_crank position sensor/vac leaks/fuel filter etc.

Mechanics only see your car for 3-4 hours at a time, you live with it so you will have a much better feeling of what triggers the issue.

Hope this helps!


Edit:
Is 93 octane in the states the same as 91 up here? 91 is more than enough for our engines.

Here we have 87/89/91/93. May save you a bit of coin

[Keshavsmith]

Thank you guys.
It doesn’t die though. It just acts like it’s going to. And only when I’m fully stopped. Other than that it’s running well. Maybe I SHOULD just take up a new hobby and try and fix it myself. But that would involve purchasing a bunch of different tools probably, right?

[Keshavsmith]

Someone else mentioned the full pressure but I’m pretty sure they checked that. I’m not sure about the fuel filter. It’s obviously somewhat fuel related as it stopped doing it for two weeks after I began filling it with premium gas. Just don’t know why it would stop and start again. I’ve ONLY put premium in it since the mechanic told me to.

[scot850]

Do you know when the fuel filter was last changed?

It could also be as simple as a bad tank of gas that had water in it.

Neil.

[Keshavsmith]

I don’t know when it was last changed. I’ll have to reference the maintenance invoices that came with the car. I wonder if I should try putting a bottle of fuel cleaner in it?

[scot850]

I don't believe it would be any harm. At least it may help point to the filter or fuel lines maybe the issue if it makes an improvement. Fairly cheap and something you can easily do yourself and no tools needed!

Neil.

[abscate]

Kesha

You will spend about one hour of labor cost to get a basic set of tools that will get you going , about $150

Don’t read too much into that fuel change. If it runs well except at idle, the Idle air valve might need cleaning