Occasional stumble at idle

patcal · Post by **patcal** » 31 Jul 2022, 17:16

Greetings all,

I have had this problem since I bought the car 2 years ago. This is my 98 S70 GLT with 137k. Be driving around just fine then all of a sudden the car will stumble & the Idle will drop for a second or 2 then recovers & everything is fine. Seems almost like a switch or something just trips & then all is good. It never stalls or lasts more then a second. Very intermittent. Hot or cold does not seem to matter. In the course of ownership I have replaced plugs, cap, rotor, cam sensor, TP sensor. I have removed & cleaned the TB. PCV system seems to be fine, good vacuum on the glove test. Compression is good. There are no codes showing & the car runs great otherwise. I really don't have a clue where to begin looking. Any thoughts? TIA.

Post by **scot850** » 31 Jul 2022, 18:17

Have you tried a fuel pump relay? Used one should be fine for comparison. I pay about $5 at junkyard for them.

When were the plug wires last changed?

Then the only 2 remaining items that I can think of are:

1) Fuel pressure/pump/fuel filter - What is your fuel pressure? For -98 should be around 43 psi.
2) Crank sensor?

Neil.

patcal · Post by **patcal** » 31 Jul 2022, 18:41

My fuel pressure was at 43-45psi when I checked it. I didn't change the wires because they are from 2014 & the car has only had about 20k since they were changed. I was looking into the relay but have not bought one yet. I will do a cross check on which other Volvos use that one & take a ride to the pick and pull. Thanks for some things to check out.

Pat

Post by **abscate** » 01 Aug 2022, 04:36

That stumble will be hard to diagnose, but of course the fuel pressure will be fine when you check it. This is one of the times you diagnose by swapping and running.

But….remove and clean your idleAir controller first….sneers from the 1999 gallery

patcal · Post by **patcal** » 01 Aug 2022, 05:57

abscate wrote: ↑01 Aug 2022, 04:36 That stumble will be hard to diagnose, but of course the fuel pressure will be fine when you check it. This is one of the times you diagnose by swapping and running.

But….remove and clean your idleAir controller first….sneers from the 1999 gallery

Thanks. I am usually against throwing parts at a problem but I think you right about swapping. I'm also going to check for corrosion at the ecu but I assumed(bad idea) that if that was the case the problem would be more consistent.