Intermittent stalling issues after heavy boost.

Boosted40 · Post by **Boosted40** » 11 Aug 2018, 21:13

Hey guys, Boosted40 here again. So, recently, I've noticed an issue after cleaning the MAF on my 2002 Volvo S40 1.9T. It's only got 126k-ish on it, and has been taken care of quite well.

So here's the symptoms, sometimes after heavy throttle usage, then letting off quickly, the car has stalled or dropped down and has seemed to had an issue in keeping up with itself so to speak. This has occured more times with the AC on, so I'm wondering if there's some kind of odd reading that is causing this. The computer isn't throwing any codes, and I'm presuming it not to be the fuel filter, as I changed that about a year ago. The plugs are pretty fresh as well.

The power steering system on my engine does get a little more usage than a normal S40, because of the suspension, so increased load between this and the AC may be a factor.

I've had it happen while turning, with the AC on and going heavy throttle, then letting off pretty quickly.
It's happened while speeding up, then letting off quickly, almost to a stop with the AC on.
And it also has seemed to almost happen going in a straight line about 35-45 mph after letting off quickly.
Going in a straight line between 35-45mph it had almost stalled after letting off quickly as well. During this time I pushed the gas pedal and it may or may not have helped.

As I type, I'm assuming the throttle closing suddenly chokes the engine out, so maybe a bad diverter valve? Anyone know where these are, or have any ideas as to what could be causing this?

Thanks again for your time, and I hope you guys have a great weekend, Boosted40

Post by **alschnertz** » 12 Aug 2018, 05:54

You may want to try cleaning the throttle body and intake air control valve.
That'd be my first step.

Boosted40 · Post by **Boosted40** » 25 Aug 2018, 20:22

Okay. I did all of this recently and it happened again one time.

I also noticed recently that under heavy load, I get a Service Light flash and a misfire for piston 3. It does not store, only pends. Yet it only happens under heavy load. I recently replaced the plugs and the filter, and even ran a different coil just to be sure. Still had this issue. I did some researching and someone said a capacitor might go bad in the harness. So that leads to either another injector, or soldering in a nee capacitor if I can. Any insight?

Post by **alschnertz** » 26 Aug 2018, 06:04

Boosted40 wrote: ↑25 Aug 2018, 20:22I also noticed recently that under heavy load, I get a Service Light flash and a misfire for piston 3. It does not store, only pends. Yet it only happens under heavy load. I recently replaced the plugs and the filter, and even ran a different coil just to be sure. Still had this issue. I did some researching and someone said a capacitor might go bad in the harness. So that leads to either another injector, or soldering in a nee capacitor if I can. Any insight?

I've been dealing with a similar issue for years.
3/4 throttle and it's fine, however, full throttle I get misses.
Thought I had it solved once by finding and replacing a cracked coil.

I recently tried another coil (Standard Products - made in China) but it made no difference.
I probably should replace both coils with factory parts.

Be sure you are using the proper plugs that are gapped correctly. Can't tell you how many people never check the gap of new plugs.
Years ago there was talk on the forums that S40s were sensitive to the spark plug brands with most people recommending "Volvo" branded plugs only. Sounded like bs to me, but I tried it. Never saw much change as compared to NGK plugs.

Never heard anything about the problem being a capacitor or injector.

jwalker275 · Post by **jwalker275** » 15 Jul 2019, 17:49

a little late to comment on your post, but you can get the replacement coil connectors from

dave barton .com

just a f.w.i.w. for ya......

jwalker275 · Post by **jwalker275** » 15 Jul 2019, 17:52

also, check that hose from the inter-cooler to the bottom of the throttle body for being bad as well.....

fairly common issue....

ÜRO PARTS 30637166

thats the replacement hose...... find it by removing the " uro parts " part and looking for it through an auto parts store, or have them run just that numeric number....

just trying to be of some help....